- Email: [email protected]
A method for assessing the relative importance of seabird breeding colonies
Biological Conservation 28 (1984) 155-172
A Method for Assessing the Relative Importance of Seabird Breeding Colonies
C. S. Lloyd* c/o Forest & Wildlife Services, Sidmonton Place, Bray, Co. Wicklow, Eire
ABSTRACT Evaluating the importance ojseabird breeding colonies in a national or international context is an essential part oj conservation planning. A method Jor assessing seabird sites, and./or selecting a series oJ key colonies, is described,Jollowing Ratcliff~,'s (1977) guidelines. The present study uses seabirds in the Republic of Ireland and data recently collected Jor a breeding seabird inventory. The method is suitable ./or use on seabird populations elsewhere. The inventory listed over 400 sites, of which 133 were identified by this study to be of national importance to conservation. Among these were 11 internationally important colonies. Thirty-one of the colonies were selected as key sites of special importance.
INTRODUCTION Conservationists often need to decide upon the relative importance of different wildlife sites. Such choices have to be made during the allocation of funds for the purchase of reserves, for example, or for the management and protection of existing ones. The method by which these judgements can be made and the most valuable sites selected has been discussed in detail by Ratcliffe (1977). * Present address: 8 Franklin Avenue, Athens. Ohio 45701, USA. 155 Biol. Conserv. 0006-3207/84/$03.00 ~' Elsevier Applied Science Publishers Ltd, England, 1984. Printed in Great Britain
156
C. S. Lloyd
A sufficiently objective method of assessment is required so that some degree of standardisation can be achieved, at least for sites in similar habitats or the same ecosystem. However, it is widely accepted in studies of this kind that the best way to test the results of a so-called objective assessment is by comparison with the assessment of the same sites on the basis of the experience and intuition of local biologists. Ideally, as Fuller (1980) points out, the method should be applied objectively even if the choice of criteria for the assessment is made rather more subjectively, by 'value judgements'. In order to be of use to conservationists, assessment of importance by reference to an accepted set of criteria must be followed by some kind of classification of each site's relative importance. Usually this is a hierarchical classification with the most valuable sites in the uppermost grouping or coming ~top of the list'. Seabirds are a particularly valuable part of the avifauna of the Irish Republic, which is otherwise rather low in diversity of breeding species compared with neighbouring countries. An estimated 40 ~o or more of the world's storm petrels Hydrobates pelagicus breed in Ireland, and other species are also well represented. Up to 29 ~o of Europe's roseate terns Sterna dougalli, approximately 18 ~o of Europe's razorbills Alca torda, and 11 ~ of the world's gannets Sula bassana nest in Irish colonies (Cramp et al., 1974, and the present study). The method specially developed to assess the importance of the different seabird breeding colonies in the Republic of Ireland in the present study was derived from similar studies by Ratcliffe (1977) and Fuller (1980), and is suitable for use on seabird colonies in other countries. Numbers of breeding seabirds are relatively well known when compared, for example, with similar data for passerine birds. Seabird numbers are comparatively easy to estimate as the species are mostly colonial nesters and conspicuous while breeding. However, accurate counts are usually difficult, if not impossible, to obtain (e.g. Seabird Group, 1980). Absolute numbers of breeding birds are not enough for a fair assessment of a colony in its national or international context since one which holds a huge number of birds of a species which is widespread and abundant elsewhere will appear to be more important than a site with a small but strong colony of a rare or endangered species. The most comprehensive data on seabird numbers in Ireland were provided by Operation Seafarer, a survey of all coastal colonies organised by the British Seabird Group and carried out in 1969/70 (Cramp et al., 1974).
Method to assess the relati~'e importance o f seabird breeding colonies
157
Since then, details of the history of various Irish colonies have been collected, and data on the size of seabird breeding populations elsewhere in Europe have become available. Both these additional sources of information are used in assessing the seabird colonies. The process has three stages (Ratcliffe, 1977): (1) Recording intrinsic site features; (2) Assessing comparative site quality; (3) Selecting the national series of key sites.
RESULTS Records of breeding seabirds An inventory of all seabird breeding sites in the Republic of Ireland was drawn up by myself in 1982, on behalf of the Forest & Wildlife Service of the Department of Fisheries and Forestry in Dublin. Published literature, unpublished reports including Operation Seafarer data for coastal sites, and private field notes were used to extract records (Lloyd, 1982a).'The aim was to provide an easily accessible source of reference to all the information available for any particular colony. The inventory also now forms a basis to which data collected in future will be added, and it highlights gaps in existing data needing to be filled by fieldwork. Nearly three-quarters (97, 73~o) of the sites considered to be of national importance by this study have been visited since Operation Seajarer (1969/70). However, no recent complete counts of breeding seabirds exist for many of these sites. Another shortcoming of the data lies in the large range in accuracy of the counts, depending on the species concerned, the inaccessibility of nest sites, the time of year and of day the counts were made, the experience of the counter and so on. Despite these difficulties, the best use has been made of the existing data for each site. Assessment of site quality The breeding seabird inventory contains over 400 sites, including some at which seabirds no longer breed. The number and diversity of species at different sites vary widely, making selection of important sites from the list extremely difficult. Ratcliffe (1977) suggested ten criteria by which sites can be assessed.
C. S. Lloyd
158
Those relevant in the present context are: 1. 2. 3. 4. 5. 6.
Diversity of species Rarity of species Recorded history of site Position in an ecological/geographical unit Potential value to nature conservation interest Intrinsic appeal.
In theory, assessment should be made completely objective by use of a scoring system for each of these criteria. Ratcliffe's study covered the whole of Britain, and use of a scoring system was considered impossible when dealing with such a large number of sites, spread over a wide area, and including all ecosystems. In practice, the criteria are not independent, data for some are lacking, and they have different values in conservation terms. Scoring systems are suitable for use only in special cases (see below). Following Ratcliffe, Fuller (1980) devised a system for assessing the ornithological interest of over 3000 sites in Britain, documented by the British Trust for Ornithology's Register of Ornithological Sites scheme. The three main attributes considered as indicators of a site's conservation value were the size of the bird populations regularly using the site, their diversity, and the rarity of the species concerned. Fuller also concluded that use of cumulative scoring for the different criteria would distort the relative importance of sites, unless only those in similar habitats were compared. Successful use of a scoring system, applied to a small number of similar ornithological sites, was demonstrated by Williams (1980), who devised an index for ranking wildfowl sites in part of southeast England (Surrey). The three constituents of the index were the site's usage or the size of the wildfowl population regularly using it, the diversity of the population (number of species), and the rarity of the species concerned in a local (west Surrey) and international (northwest Europe) context. The following criteria were chosen to assess seabird colonies in the present study: 1. 2. 3. 4. 5.
Community quality at national level Population size Population diversity Rarity of species at (a) national, and (b) international levels Additional interests.
Method to assess the relative importance o f seabird breeding colonies
159
Community quality More than ten years ago, ornithologists working with wildfowl suggested a 1 ~o criterion for the recognition of areas of special importance to wintering ducks, geese and swans (Atkinson-Willes, 1976). This proposal, formally adopted by the International Conference on the Conservation of Wetlands and Waterfowl held at Heiligenhafen (W Germany) in December 1974, states that any site which regularly supports 1 ~ or more of the birds of an entire species, or of a recognisable flyway or migratory population, or of any other clearly defined (biogeographic) population should be regarded as being of international importance. This criterion is used widely for assessing the importance of wetlands for wintering birds (e.g. Hutchinson, 1979). It has the advantage of being relatively easy to apply to any species, once an estimate of its local population size has been obtained. It also tends to favour species which gather into flocks for feeding, roosting or loafing (i.e. resting, preening etc.), or which do so because they require specialised habitat with restricted distribution. The same criterion has been extended to cover other birds, including seabirds, and to breeding birds (Scott, 1980) so that any area which regularly supports 1 ~o or more of the breeding birds (pairs) of a recognisable population of any species is regarded as being of international importance. By extrapolation, any site holding 1 ~o or more of a country's total breeding population of the species is considered to be of national importance. The 1 ~ criterion is now generally accepted by ornithologists and has been adopted here for breeding populations of seabirds. The results obtained by application of the criteria for national and international importance compare favourably with a list of important sites (now a little out of date) drawn up using the experience and subjective impressions of Irish ornithologists. This list was made in 1980 by the Irish Wildbird Conservancy, on behalf of the International Council for Bird Preservation (Osiek & M6rzer Bruyns, 1981). The choice of the 1 ~o level, as opposed to 0.5 or 2 ~o levels, for example, is purely subjective in this as in all other similar studies. However, the results do pass the generally accepted test of being in agreement with existing intuitive site selections. An initial assessment of Irish seabird colonies was made on the basis of the 1 ~o criteria for national and international importance. Estimates of seabird populations were obtained from Operation Seafarer data, updated to allow for the inland colonies, mainly of gulls (Whilde, 1978,
C. S. Lloyd
160
pers. comm.); the decline in numbers of breeding roseate terns (Thomas, 1982); and the under-estimate in the 1969/70 figure for black guillemots Cepphus grylle, breeding in Ireland (O. J. Merne et al., pers. comm.). However, it must be stressed again that these data vary widely in their accuracy, mainly because of the difficulties involved in censusing seabirds precisely; particularly affected are the nocturnal, burrow-nesting petrels and the auks (e.g. Evans & Birkhead, 1982). The critical 1 ~o levels were obtained from the estimated population totals (Table 1). International importance in the present study was considered on a northwest European scale, excluding Iceland (apart from its gannetries) TABLE 1 Species' P o p u l a t i o n Levels U s e d as C r i t e r i a for N a t i o n a l o r I n t e r n a t i o n a l I m p o r t a n c e (All figures in pairs)
Species
Fulmar Manx shearwater S t o r m petrel Gannet Cormorant Shag B l a c k - h e a d e d gull C o m m o n gull Lesser b l a c k - b a c k e d gull H e r r i n g gull G r e a t b l a c k - b a c k e d gull Kittiwake S a n d w i c h tern R o s e a t e tern C o m m o n tern A r c t i c tern Little tern Guillemot Razorbill Black guillemot Puffin
1 ','70oJ Irish population
1 "//ooJ European population
170 600 = high 0/3 1 200 = low o/4 200 20 25 175 30 55 600 35 350 5 5 25 10 5 525 300 10 250
7 000 3 000 = 0/4 2 000 = o/4 1 600 ------15 000 400 5 500 13 000 50 25 000 2 000 -25 000
1 ')"0 of world population
0,,'4 o/4 2 000 -----
---
--2 500 --
O r d e r 3 (0/3) = 101 - 1 000 pairs, o r d e r 4 (0/4) = 1 001 - 10 000 pairs. Latin n a m e s are given in T a b l e 3. - - , E s t i m a t e only available for 1 ~o level; all are far in excess o f largest Irish c o l o n i e s , e . g . c . 400 c o r m o r a n t s , 1 000 shags.
Method to assess the relatil'e importance oJseabird breeding colonies
161
nk
|0
Z •
ml
4~
Fig. 1. Seabird sites specially selected by this study • = Nationally important colonies, ® = Key sites of national importance. Internationally important colonies: 1, Hom Head, Co. Donegal. 2, Cliffs of Moher, Co. Clare. 3, Inishtooskert, Co. Kerry. 4, Inishnabro, Inishtearaght & Inishvickillaun, Co. Kerry. 5, Great & Little Skellig, Co. Kerry.6, Puffin Island, Co. Kerry. 7, Saltee islands, Co. Wexford. 8, Lady's Island Lake, Co. Wexford.
C. S. Lloyd
162
and the islands of the arctic for which few census data exist. The area contains a natural biogeographic population of all Irish species; indeed the storm petrel and Manx shearwater Puffinus puffinus puffinus (a subspecies of the cosmopolitan common shearwater) breed regularly nowhere else in the world. Published population estimates for each species were used wherever possible (Scott, 1980; Bullock & Gomersall, 1981; Thomas, 1982), and very approximate estimates were made for inland gull populations. The sites listed in the inventory at which seabirds no longer breed and those with small numbers of nesting birds of the commoner species were excluded by the initial assessment. A list of 133 sites holding colonies of national importance for one or more seabird species was obtained (Fig. 1). Among these sites were 11 of international importance for one or more species (Table 2). Many of the sites 'discarded' at this stage in the analysis TABLE 2 Seabird Colonies of International Importance in Ireland
Colony Horn Head, Co. Donegal Cliffs of Moher, Co. Clare Inishtooskert, Co. Kerry Inishtearaght, Co. Kerry
European importance
mid o/5 P (1972)
Inishnabro, Co. Kerry Inishvickillaun, Co. Kerry Puffin Island, Co. Kerry Great Skellig, Co. Kerry Little Skellig, Co. Kerry Saltee Islands, Co. Wexford Lady's Island Lake, Co. Wexford
low 0/5 P (1973)
Worm importance 13 000i R (1980) 2 900 R (1980) 0/4 SP (1969)mid 0/5 MS (1972) f l 000 SP (1973) 5 000- 7 000 R (1973) o/5 (1974) o/4 MS (1980) o/4 SP (1974) low 0/4 MS (1973) o/4 SP (1973) 20 000 G (1970) c. 6000i R (1981)
~ ~
275 RT (1981)
Figures are estimated numbers of pairs or individual birds (i). Order 4 (o/4), 1 001 - 10 000 pairs; order 5 (o/5), 10001-100 000 pairs. MS, Manx shearwater; SP, storm petrel; G. gannet; RT, roseate tern; R. razorbill; P, puffin. In addition to these colonies, the Blasket Islands (which include Inishtooskert, Inishtearaght, Inishnabro, Inishvickillaun, Great Blasket & islets nearby) supported (1969-73) 900 great black-backed gulls and 26200 puffins, and are thus of European importance f o r both species. Years of observation are given in parentheses above.
Method to assess the relative importance oj seabird breeding colonies
163
were recognised to be of potential value for conservation on a local basis and may increase in importance should the size or composition of their breeding populations change in future. The threshold 1 ~ of the national breeding population was more frequently met by the species of seabirds studied than would have been the case, for example, in non-colonial species. None of the colonies omitted from the list of nationally important sites were considered to have been wrongly excluded.
SIZE, DIVERSITY AND RARITY Three of the remaining criteria were used together, in the next stage of analysis, to assess the value of the 133 sites listed. Size The size of the breeding population was considered to be important because of the gregarious nature of almost all seabird" species. Concentrations of nesting seabirds readily attract others. Terns prefer to breed in the vicinity of nesting gulls of small species such as black-headed gulls Larus ridibundus (e.g. Koskimies, 1957), auks nesting on a cliff attract other birds, usually non-breeding visitors (Harris, 1976; Lloyd, 1982b), and newly established gannet colonies grow mainly through immigration of breeding birds (Nelson, 1978); one in Ireland, for example, increased by 50 ~ per annum at the peak of immigration (Lloyd, 1982b). The sites were separated into three categories according to the total size of their seabird breeding populations. Broad categories were chosen deliberately to make allowance for irregularities in the census data. The thresholds of the categories had to be selected arbitrarily but the results were tested by comparison with intuitive judgements made by myself and other ornithologists. Colony size (approximate) Category A. 5000+ pairs Category B. 1000-4999 pairs Category C. 500--999 pairs.
The largest colonies (14, 10-5~o of those listed) fell into category A, 30 (22.5 ~) into category B, 25 (19 ~) into category C, and the remaining 64 (48 ~o) were too small to be categorised.
C. S. Lloyd
164
Diversity Seabird colonies naturally tend to contain at least two or three different species nesting together. It can be argued that, in conservation terms, a colony can be considered more stable if it has several different breeding species. In addition, such colonies often provide a spectacle of intrinsic merit and education potential for the public (see below). Diversity was measured by the number of breeding species most recently recorded at each seabird site. The categories of diversity were selected as before by trial and error, and checked by reference to intuition.
Colony diversity Category A. Category B. Category C.
11 or more breeding species 9 or 10 breeding species 7 or 8 breeding species.
Twenty-one seabird species regularly breed in Ireland. In addition to these, the Leach's petrel Oceanodroma leucorhoa was proved to be nesting on the Stags of Broadhaven, inaccessible stacks off the northwest of Co. Mayo, in 1982 (Irish Wildlife Conservancy, 1982). This was the first record of breeding by this species in about 70 years, and the Leach's petrel is considered to be a rare and little known nesting species. It has been omitted for the purpose of the present study. Fourteen sites (10.5 ~ of those listed) were placed in category A, 19 (14 ~ ) in category B, 29 (22 ~o) in category C, and 71 (53 ~o) were not sufficiently diverse to be categorised.
Rarity The rarity of only those species for which each site was of national importance was assessed. The reasons for this were to remove the biasing effect of casual breeding species and those present in only very small numbers. (Rare species present in small numbers were included as they were usually at or above the critical 1 ~o level.) Rarity in national and international contexts were examined separately because of the differing status of most species in each context.
National rarity. The rarity of each species on a national scale was scored from one to ten, depending on its total Irish breeding population (Table 3): < 1000 1001-5000 5001-10 000 10 001-15 000 15 001-20 000
pairs pairs pairs pairs pairs
= = = = =
10 9 8 7 6
20 001-25 000 25 001-30 000 30 001-35 000 35 001-40 000 > 40 000
pairs pairs pairs pairs pairs
= = = = =
5 4 3 2 1
Method to assess the relative importance of seabird breeding colonies
165
TABLE 3
Rarity Scores for Irish Seabirds Species
Fulmar Fulmarus glacialis Manx shearwater Puffinus puffinus Storm petrel Hydrobates pelagicus Gannet Sula bassana Cormorant Phalacrocorax carbo Shag Phalacrocorax aristotelis Black-headed gull Larus ridibundus Common gull Larus canus Lesser black-backed gull Larus fuscus Herring gull Larus argentatus Great black-backed gull Larus marinus Kittiwake Rissa tridactyla Sandwich tern Sterna sandvicensis Roseate tern Sterna dougalli Common tern Sterna hirundo Arctic tern Sterna paradisea Little tern Sterna albifrons Guillemot Uria aalge Razorbill Alca torda Black guillemot Cepphus grylle Puffin Fratercula arctica
Score for total Irish population
Score for approx. °/o N W European population
6
2
1 1
5
5 9 9 6 9 8
10 4 2 2 2 2 2
1
2
9 2 10 10 9 9 10
2 2 2 7 2 1 2
1
2
3 9 5
5 2 2
See text for sources of data and explanation of scores. However, the importance of certain species, and hence the colonies in which they nest, is under-rated using this system alone. For example, a considerable proportion of the world populations of both the storm petrel and the razorbill breed in Ireland. Both these species have large Irish populations and score only 1 and 3 respectively in Table 3. Clearly, a species' abundance on an international, as well as a national, scale is of relevance to its value in conservation terms. I n t e r n a t i o n a l rarity. The 21 species of seabirds breeding in Ireland were classed according to their abundance in northwest Europe by reference to the Irish population of each species as a proportion of the total estimated European population. The accuracy with which the latter can be estimated varies from species to species. F o r example, the total number of
166
C. S. Lloyd
gannets, which occur in only 29 breeding colonies in Europe, can be estimated far more accurately than that of black-headed gulls which breed extensively both inland throughout central Europe and on the coasts. A score for the rarity of each species on an international scale was devised with a range from one to ten (Table 3): <1~=1 1-5 ~o = 2 6-10~= 3 11--15~=4 16-20~ = 5
21-25~=6 26-30 ~ = 7 31-35~=8 36-40~ = 9 > 4 0 ~ o = 10
On this scale, the storm petrel received a score of 10 and the razorbill one of 5. Each site listed thus received two rarity scores referring to its nationally important species. The first was the sum of the species' scores on the national rarity scale, and the second the total score on the international rarity scale. Categories for these values were chosen by the same method used for the other criteria.
National rarity International rarity Category A. Category B. Category C.
32 + 25-31 18-24
14 + 10-13 6-9
Fifty-nine sites (44 ~o of those listed) were categorised for their species' rarity within Ireland, and 44 (33 ~ ) for the rarity of their species in an international context (Table 4). TABLE 4
Number of Sites in Each Species Rarity Category Category
National rarity
A B C
14 (10.5 ~o) 14(10"5~o) 31 (23~o)
International rarity 15 (11 "/~/o, 9 (7~) 20 (15~o)
Percentages are proportions of 133 listed sites.
Method to assess the relative importance o f seabird breeding colonies
167
Additional interests Seventy-five (56~o) of the 133 sites under consideration possessed additional attributes, not covered by the criteria described so far. Most of these attributes were of value in conservation terms, but Ratcliffe's (1977) recommendation was adopted that such features be considered as secondary to the intrinsic properties of the site. Additional interests included the following: (i)
Well-documented history, e.g. Saltee islands, Co. Wexford, have records for 54 of the years between 1851 and 1982. (ii) Some aspect of uniqueness in a local context, e.g. the furthest south common gull Larus canus colony (Eyeries Island, Co. Cork) or the only cliff colony in the county (Aughris Head, Co. Sligo). (iii) Site of long-term ringing study or other research, e.g. Inishglora, Co. Mayo. (iv) Educational potential or other potential for conservation, e.g. Howth Head, a colony of over 3000 seabirds within the city limits of Dublin. (v) Intrinsic appeal, e.g. Cliffs of Moher, Co. Clare. (vi) Inland colony of gulls, terns or cormorants Phalacrocorax carbo. These were once abundant in northwest Ireland but are now relatively rare. (vii) Presence of internationally important numbers of one or more species, e.g. sites listed in Table 2. (viii) Site of a gannetry; there are only four in Ireland. (ix) Diversity of non-seabird breeding species, if known (BTO Register of Ornithological Sites). Selection of key sites The final stage in this analysis was the consideration of the site assessments and the selection of nationally important key sites. The aim was to produce a listing' which could be used and relied upon by conservationists, and a hierarchical grouping, however broadly defined, was concluded to give best value to the selection. Methods used in earlier studies were examined. The selection method used by Williams (1980) to evaluate wildfowl sites was to rank indices. The index for each site was obtained from the product of values for each of the three main constituents (usage, rarity, diversity).
168
c. s. Lloyd
The final list of sites in order of rank made no allowance for the amount of difference in importance between the sites. Both Ratcliffe (1977) and Fuller (1980) avoid the use of cumulative scoring of assessment criteria but instead grade the sites, placing those of similar value together. Fuller uses five categories with different levels of importance in conservation value. These are international (A), national (B), regional (C), county (D) and local (E). (The categories A, B and C used in the present study are considered to be approximately equivalent to Fuller's B, C and D respectively.) An example of a typical final assessment of a seabird colony is given in which the site has one attribute at level A, one at level B, 2 at level D and 2 at level E. This type of assessment obscures less of the valuable information than a ranked listing, for example. However, the result is a rather loose hierarchy which cannot be interpreted so literally when making direct comparison of sites. The best selection method should be intermediate between these two. Three different ways of selecting key sites were considered in the present study. The first two used cumulative scoring which, Ratcliffe and Fuller suggest, are best suited to the comparison of sites in similar habitat. The categories (A, B and C) into which assessments of the four criteria (size, diversity, Irish rarity, international rarity) were placed were given numerical values. These were either added together (Method 1; A = 3, B = 2, C = 1) or multiplied (Method 2; A = 4, B = 3, C = 2) to give a final index value. The top four groupings obtained by method 1 contained only 7 ~o of the colonies, and the same groups arrived at by method 2 contained 1 3 ~ of the colonies. These methods were considered unsatisfactory because they produced fragmentary groupings and required additional numerical interpretation of the categories. They were rejected in favour of the third method. This method was based simply upon the number of assessment criteria which fell into category A for each colony (Table 5). Sites with four As were considered to be of major national importance as key sites, probably equivalent to Grade I sites in Ratcliffe's (1977) study. Sites with three criteria in the A category were of similar or slightly inferior merit, approximately equivalent to Ratcliffe's Grade II, and were regarded as alternatives to the four A sites. Sites with two A category attributes were recognised to be of minor national importance but high regional importance as key sites (Grade III), and those with a single A were of lower regional importance but still chosen as key sites (Grade IV). Thirtyone sites, nearly a quarter (23 ~) of those listed, were selected by this
Method to assess the relatit'e importance of seabird breeding colonies
169
TABLE 5
Selection of Key Seabird Sites Grade I: 4 As.
Grade 111:2 As.
Saltees, Co. Wexford (7) Inishnabro, Co. Kerry (5) Lambay, Co. Dublin (2)
Inishmore, Co. Galway (1) Magharee Islands, Co. Kerry (1) Inishtooskert, Co. Kerry (1) Cape Clear Island, Co. Cork (1)
Grade 11:3 As.
Grade 1V." 1 A.
Puffin Island, Co. Kerry (5) Clare Island, Co. Mayo (3) Inishtearaght, Co. Kerry (3) Grade I11:2 As.
Cliffs of Moher, Co. Clare (4) Great Skellig, Co. Kerry (4) Horn Head, Co. Donegal (3) Roaninish, Co. Donegal (3) Inishvickillaun, Co. Kerry (3) Bull Rock, Co. Cork (3) lnishglora, Co. Mayo (1) Inishturk, Co. Mayo (1)
Little Skellig, Co. Kerry (5) Lady's Island Lake, Co. Wexford (4) Illaunmaster, Co. Mayo (2) Tory Island, Co. Donegal (1) Tormore, Co. Donegal (1) Duvillaun Islands, Co. Mayo (1) Great Blasket & islets, Co. Kerry (1) Inishowen-Balbane Hds, Co. Donegal Inishmurray, Co. Sligo Benwee Head, Co. Mayo Inishkea Islands, Co. Mayo Scariff, Co. Kerry Kenmare Bay, Co. Kerry
Figures in brackets refer to number of additional interesting features associated with each site; see text for details. In direct comparison of sites, attributes in categories B and C should also be taken into account.
method. Although categories B and C played no part in the choice of key sites, they were useful for direct comparison of sites.
CONCLUSIONS Both Ratcliffe (1977) and Fuller (1980) stress that site assessment and selection should be preceded by the implementation of a strict policy for site boundary demarcation. Otherwise the quality of a site could reflect the extent and diversity of its area. This is as relevant to seabird sites as it was to the wider range of sites examined by these authors, and it is one way in which the present study could have been improved, had the necessary data been available. The procedure described here for site assessment and selection can be used with few modifications to examine the importance of seabird
170
C. S. Lloyd
colonies outside Ireland, given a knowledge of the estimated total breeding populations of each species on a national and northwest European (or other suitable biogeographic) scale. To summarise, the basic steps are as follows: 1. 2. 3. 4. 5. 6a 7. 8. 9.
Calculation of 1 ~o national and international population levels. Selection of colonies with one or more species at the national level of abundance or above. Obtain approximate total number of regularly/recently breeding birds at each site. Obtain number of regularly/recently breeding species for each site. Devise scoring system for rarity of each species on (a) national scale, and (b) international scale. & 6b. Calculation of total rarity score, on each scale, for species breeding in nationally important numbers at each site !(see 2). List additional features of interest/conservation value at each site. Derive suitable limits to categories A, B and C for the attributes in 3, 4, 6a and 6b above. Selection of key colonies, with 4 As, 3 As, 2 As and 1 A, and grade accordingly.
The relative importance of different seabird colonies is a dynamic property. It is essential that an up-to-date seabird inventory be maintained for Irish colonies so that re-assessment can be made on a regular, if not annual, basis. New data on breeding numbers will become available for individual colonies, for the Irish populations of each species, and for northwest European populations. Meanwhile, plans for the creation of specially protected areas, the purchase of land for reserves, the development of sites with educational potential and other measures for seabird conservation in Ireland can take into account the existence of colonies which have been identified by this study as being of key national importance.
ACKNOWLEDGEMENTS I am grateful to the Forest & Wildlife Service of the Department of Forestry & Fisheries, Dublin, who provided the funding for this study, and to Oscar Merne who gave valuable advice and encouragement through his supervision. The manuscript of this paper was improved by
Method to assess the relative importance of seabird breeding colonies
171
comments from R. J. Fuller, an a n o n y m o u s referee, and Dr M. P. Harris. Unpublished information was m a d e available to me for the breeding seabird inventory by Dr D. Cabot, M. O'Meara, Dr A. Whilde, Dr K. Partridge, H. Brazier, O. J. Merne and Dr G. J. Thomas.
REFERENCES Atkinson-Willes, G. L. (1976). The numerical distribution of ducks, swans and coots as a guide in assessing the importance of wetlands in winter. Proc. int. ConJl on Conservation of Wetlands and WaterJowl, Heiligenhafen, 1974, ed. by M. Smart, 199-254. Bullock, I. D. & Gomersall, R. (1981). The breeding populations of terns in Orkney and Shetland in 1980. Bird Study, 28, 187-200. Cramp, S., Bourne, W. R. P. & Saunders, D. (1974). The seabirds of Britain and Ireland. London, Collins. Evans, P. G. H. & Birkhead, T. R. (1982). Editorial. Seabird Report, 6, 3-4. Fuller, R. J. (1980). A method for assessing the ornithological interest of sites for conservation. Biol. Conserv., 17, 229-39. Harris, M. P. (1976). Inter-colony movements of Farne Islands puffins. Trans. nat. Hist. Soc. Northumb., 42, 115-18. Hutchinson, C. D. (1979). Ireland's wetlands and their birds. Dublin, Irish Wildbird Conservancy. Irish Wildbird Conservancy. (1982). Leach's petrels in Co. Mayo. IWC News, No. 33, 3. Koskimies, J. (1957). Terns and gulls as features of habitat recognition for birds nesting in colonies. Orn. Fenn., 34, 1-6. Lloyd, C. S. (1982a). An inventory Q['seabird breeding colonies in the Republic oj Ireland. Unpublished data and report, Forest & Wildlife Service, Dublin. Lloyd, C. S. (1982b). The seabirds of Great Saltee. Irish Birds, 2, 1-37. Nelson, B. (1978). The Gannet. Berkhamsted, T. & A. D. Poyser. Osieck, E. R. & M6rzer Bruyns, M. F. (1981). Important bird areas in the European community. Unpublished report prepared by the International Council for Bird Preservation, Cambridge, for the Environment & Consumer Protection Service of the Commission of the European Communities. Ratcliffe, D. A. (ed.). (1977). A nature conservation rev&w, 1. Cambridge, Cambridge University Press. Scott, D. D. (1980). Contribution to the determination of special protection areas Jbr the conservation of birds. Unpublished report prepared by the International Wildfowl Research Bureau, Slimbridge, for the Environment & Consumer Protection Service of the Commission of the European Communities. Seabird Group (1980). The auk censusing manual, Sheffield, England.
172
C. S. Lloyd
Thomas, G. J. (1982). Breeding terns in Britain and Ireland, 1975-79. Seabird Report, 6, 59-69. Whilde, A. (1978). A survey of gulls breeding inland in the west of Ireland in 1977 and 1978 and a review of the inland breeding habit in Ireland and Britain. Irish Birds, 1, 134-60. Williams, G. (1980). An index for the ranking of wildfowl habitats, as applied to eleven sites in west Surrey, England. Biol. Conserv., 18, 93-9.
A Method for Assessing the Relative Importance of Seabird Breeding Colonies
C. S. Lloyd* c/o Forest & Wildlife Services, Sidmonton Place, Bray, Co. Wicklow, Eire
ABSTRACT Evaluating the importance ojseabird breeding colonies in a national or international context is an essential part oj conservation planning. A method Jor assessing seabird sites, and./or selecting a series oJ key colonies, is described,Jollowing Ratcliff~,'s (1977) guidelines. The present study uses seabirds in the Republic of Ireland and data recently collected Jor a breeding seabird inventory. The method is suitable ./or use on seabird populations elsewhere. The inventory listed over 400 sites, of which 133 were identified by this study to be of national importance to conservation. Among these were 11 internationally important colonies. Thirty-one of the colonies were selected as key sites of special importance.
INTRODUCTION Conservationists often need to decide upon the relative importance of different wildlife sites. Such choices have to be made during the allocation of funds for the purchase of reserves, for example, or for the management and protection of existing ones. The method by which these judgements can be made and the most valuable sites selected has been discussed in detail by Ratcliffe (1977). * Present address: 8 Franklin Avenue, Athens. Ohio 45701, USA. 155 Biol. Conserv. 0006-3207/84/$03.00 ~' Elsevier Applied Science Publishers Ltd, England, 1984. Printed in Great Britain
156
C. S. Lloyd
A sufficiently objective method of assessment is required so that some degree of standardisation can be achieved, at least for sites in similar habitats or the same ecosystem. However, it is widely accepted in studies of this kind that the best way to test the results of a so-called objective assessment is by comparison with the assessment of the same sites on the basis of the experience and intuition of local biologists. Ideally, as Fuller (1980) points out, the method should be applied objectively even if the choice of criteria for the assessment is made rather more subjectively, by 'value judgements'. In order to be of use to conservationists, assessment of importance by reference to an accepted set of criteria must be followed by some kind of classification of each site's relative importance. Usually this is a hierarchical classification with the most valuable sites in the uppermost grouping or coming ~top of the list'. Seabirds are a particularly valuable part of the avifauna of the Irish Republic, which is otherwise rather low in diversity of breeding species compared with neighbouring countries. An estimated 40 ~o or more of the world's storm petrels Hydrobates pelagicus breed in Ireland, and other species are also well represented. Up to 29 ~o of Europe's roseate terns Sterna dougalli, approximately 18 ~o of Europe's razorbills Alca torda, and 11 ~ of the world's gannets Sula bassana nest in Irish colonies (Cramp et al., 1974, and the present study). The method specially developed to assess the importance of the different seabird breeding colonies in the Republic of Ireland in the present study was derived from similar studies by Ratcliffe (1977) and Fuller (1980), and is suitable for use on seabird colonies in other countries. Numbers of breeding seabirds are relatively well known when compared, for example, with similar data for passerine birds. Seabird numbers are comparatively easy to estimate as the species are mostly colonial nesters and conspicuous while breeding. However, accurate counts are usually difficult, if not impossible, to obtain (e.g. Seabird Group, 1980). Absolute numbers of breeding birds are not enough for a fair assessment of a colony in its national or international context since one which holds a huge number of birds of a species which is widespread and abundant elsewhere will appear to be more important than a site with a small but strong colony of a rare or endangered species. The most comprehensive data on seabird numbers in Ireland were provided by Operation Seafarer, a survey of all coastal colonies organised by the British Seabird Group and carried out in 1969/70 (Cramp et al., 1974).
Method to assess the relati~'e importance o f seabird breeding colonies
157
Since then, details of the history of various Irish colonies have been collected, and data on the size of seabird breeding populations elsewhere in Europe have become available. Both these additional sources of information are used in assessing the seabird colonies. The process has three stages (Ratcliffe, 1977): (1) Recording intrinsic site features; (2) Assessing comparative site quality; (3) Selecting the national series of key sites.
RESULTS Records of breeding seabirds An inventory of all seabird breeding sites in the Republic of Ireland was drawn up by myself in 1982, on behalf of the Forest & Wildlife Service of the Department of Fisheries and Forestry in Dublin. Published literature, unpublished reports including Operation Seafarer data for coastal sites, and private field notes were used to extract records (Lloyd, 1982a).'The aim was to provide an easily accessible source of reference to all the information available for any particular colony. The inventory also now forms a basis to which data collected in future will be added, and it highlights gaps in existing data needing to be filled by fieldwork. Nearly three-quarters (97, 73~o) of the sites considered to be of national importance by this study have been visited since Operation Seajarer (1969/70). However, no recent complete counts of breeding seabirds exist for many of these sites. Another shortcoming of the data lies in the large range in accuracy of the counts, depending on the species concerned, the inaccessibility of nest sites, the time of year and of day the counts were made, the experience of the counter and so on. Despite these difficulties, the best use has been made of the existing data for each site. Assessment of site quality The breeding seabird inventory contains over 400 sites, including some at which seabirds no longer breed. The number and diversity of species at different sites vary widely, making selection of important sites from the list extremely difficult. Ratcliffe (1977) suggested ten criteria by which sites can be assessed.
C. S. Lloyd
158
Those relevant in the present context are: 1. 2. 3. 4. 5. 6.
Diversity of species Rarity of species Recorded history of site Position in an ecological/geographical unit Potential value to nature conservation interest Intrinsic appeal.
In theory, assessment should be made completely objective by use of a scoring system for each of these criteria. Ratcliffe's study covered the whole of Britain, and use of a scoring system was considered impossible when dealing with such a large number of sites, spread over a wide area, and including all ecosystems. In practice, the criteria are not independent, data for some are lacking, and they have different values in conservation terms. Scoring systems are suitable for use only in special cases (see below). Following Ratcliffe, Fuller (1980) devised a system for assessing the ornithological interest of over 3000 sites in Britain, documented by the British Trust for Ornithology's Register of Ornithological Sites scheme. The three main attributes considered as indicators of a site's conservation value were the size of the bird populations regularly using the site, their diversity, and the rarity of the species concerned. Fuller also concluded that use of cumulative scoring for the different criteria would distort the relative importance of sites, unless only those in similar habitats were compared. Successful use of a scoring system, applied to a small number of similar ornithological sites, was demonstrated by Williams (1980), who devised an index for ranking wildfowl sites in part of southeast England (Surrey). The three constituents of the index were the site's usage or the size of the wildfowl population regularly using it, the diversity of the population (number of species), and the rarity of the species concerned in a local (west Surrey) and international (northwest Europe) context. The following criteria were chosen to assess seabird colonies in the present study: 1. 2. 3. 4. 5.
Community quality at national level Population size Population diversity Rarity of species at (a) national, and (b) international levels Additional interests.
Method to assess the relative importance o f seabird breeding colonies
159
Community quality More than ten years ago, ornithologists working with wildfowl suggested a 1 ~o criterion for the recognition of areas of special importance to wintering ducks, geese and swans (Atkinson-Willes, 1976). This proposal, formally adopted by the International Conference on the Conservation of Wetlands and Waterfowl held at Heiligenhafen (W Germany) in December 1974, states that any site which regularly supports 1 ~ or more of the birds of an entire species, or of a recognisable flyway or migratory population, or of any other clearly defined (biogeographic) population should be regarded as being of international importance. This criterion is used widely for assessing the importance of wetlands for wintering birds (e.g. Hutchinson, 1979). It has the advantage of being relatively easy to apply to any species, once an estimate of its local population size has been obtained. It also tends to favour species which gather into flocks for feeding, roosting or loafing (i.e. resting, preening etc.), or which do so because they require specialised habitat with restricted distribution. The same criterion has been extended to cover other birds, including seabirds, and to breeding birds (Scott, 1980) so that any area which regularly supports 1 ~o or more of the breeding birds (pairs) of a recognisable population of any species is regarded as being of international importance. By extrapolation, any site holding 1 ~o or more of a country's total breeding population of the species is considered to be of national importance. The 1 ~ criterion is now generally accepted by ornithologists and has been adopted here for breeding populations of seabirds. The results obtained by application of the criteria for national and international importance compare favourably with a list of important sites (now a little out of date) drawn up using the experience and subjective impressions of Irish ornithologists. This list was made in 1980 by the Irish Wildbird Conservancy, on behalf of the International Council for Bird Preservation (Osiek & M6rzer Bruyns, 1981). The choice of the 1 ~o level, as opposed to 0.5 or 2 ~o levels, for example, is purely subjective in this as in all other similar studies. However, the results do pass the generally accepted test of being in agreement with existing intuitive site selections. An initial assessment of Irish seabird colonies was made on the basis of the 1 ~o criteria for national and international importance. Estimates of seabird populations were obtained from Operation Seafarer data, updated to allow for the inland colonies, mainly of gulls (Whilde, 1978,
C. S. Lloyd
160
pers. comm.); the decline in numbers of breeding roseate terns (Thomas, 1982); and the under-estimate in the 1969/70 figure for black guillemots Cepphus grylle, breeding in Ireland (O. J. Merne et al., pers. comm.). However, it must be stressed again that these data vary widely in their accuracy, mainly because of the difficulties involved in censusing seabirds precisely; particularly affected are the nocturnal, burrow-nesting petrels and the auks (e.g. Evans & Birkhead, 1982). The critical 1 ~o levels were obtained from the estimated population totals (Table 1). International importance in the present study was considered on a northwest European scale, excluding Iceland (apart from its gannetries) TABLE 1 Species' P o p u l a t i o n Levels U s e d as C r i t e r i a for N a t i o n a l o r I n t e r n a t i o n a l I m p o r t a n c e (All figures in pairs)
Species
Fulmar Manx shearwater S t o r m petrel Gannet Cormorant Shag B l a c k - h e a d e d gull C o m m o n gull Lesser b l a c k - b a c k e d gull H e r r i n g gull G r e a t b l a c k - b a c k e d gull Kittiwake S a n d w i c h tern R o s e a t e tern C o m m o n tern A r c t i c tern Little tern Guillemot Razorbill Black guillemot Puffin
1 ','70oJ Irish population
1 "//ooJ European population
170 600 = high 0/3 1 200 = low o/4 200 20 25 175 30 55 600 35 350 5 5 25 10 5 525 300 10 250
7 000 3 000 = 0/4 2 000 = o/4 1 600 ------15 000 400 5 500 13 000 50 25 000 2 000 -25 000
1 ')"0 of world population
0,,'4 o/4 2 000 -----
---
--2 500 --
O r d e r 3 (0/3) = 101 - 1 000 pairs, o r d e r 4 (0/4) = 1 001 - 10 000 pairs. Latin n a m e s are given in T a b l e 3. - - , E s t i m a t e only available for 1 ~o level; all are far in excess o f largest Irish c o l o n i e s , e . g . c . 400 c o r m o r a n t s , 1 000 shags.
Method to assess the relatil'e importance oJseabird breeding colonies
161
nk
|0
Z •
ml
4~
Fig. 1. Seabird sites specially selected by this study • = Nationally important colonies, ® = Key sites of national importance. Internationally important colonies: 1, Hom Head, Co. Donegal. 2, Cliffs of Moher, Co. Clare. 3, Inishtooskert, Co. Kerry. 4, Inishnabro, Inishtearaght & Inishvickillaun, Co. Kerry. 5, Great & Little Skellig, Co. Kerry.6, Puffin Island, Co. Kerry. 7, Saltee islands, Co. Wexford. 8, Lady's Island Lake, Co. Wexford.
C. S. Lloyd
162
and the islands of the arctic for which few census data exist. The area contains a natural biogeographic population of all Irish species; indeed the storm petrel and Manx shearwater Puffinus puffinus puffinus (a subspecies of the cosmopolitan common shearwater) breed regularly nowhere else in the world. Published population estimates for each species were used wherever possible (Scott, 1980; Bullock & Gomersall, 1981; Thomas, 1982), and very approximate estimates were made for inland gull populations. The sites listed in the inventory at which seabirds no longer breed and those with small numbers of nesting birds of the commoner species were excluded by the initial assessment. A list of 133 sites holding colonies of national importance for one or more seabird species was obtained (Fig. 1). Among these sites were 11 of international importance for one or more species (Table 2). Many of the sites 'discarded' at this stage in the analysis TABLE 2 Seabird Colonies of International Importance in Ireland
Colony Horn Head, Co. Donegal Cliffs of Moher, Co. Clare Inishtooskert, Co. Kerry Inishtearaght, Co. Kerry
European importance
mid o/5 P (1972)
Inishnabro, Co. Kerry Inishvickillaun, Co. Kerry Puffin Island, Co. Kerry Great Skellig, Co. Kerry Little Skellig, Co. Kerry Saltee Islands, Co. Wexford Lady's Island Lake, Co. Wexford
low 0/5 P (1973)
Worm importance 13 000i R (1980) 2 900 R (1980) 0/4 SP (1969)mid 0/5 MS (1972) f l 000 SP (1973) 5 000- 7 000 R (1973) o/5 (1974) o/4 MS (1980) o/4 SP (1974) low 0/4 MS (1973) o/4 SP (1973) 20 000 G (1970) c. 6000i R (1981)
~ ~
275 RT (1981)
Figures are estimated numbers of pairs or individual birds (i). Order 4 (o/4), 1 001 - 10 000 pairs; order 5 (o/5), 10001-100 000 pairs. MS, Manx shearwater; SP, storm petrel; G. gannet; RT, roseate tern; R. razorbill; P, puffin. In addition to these colonies, the Blasket Islands (which include Inishtooskert, Inishtearaght, Inishnabro, Inishvickillaun, Great Blasket & islets nearby) supported (1969-73) 900 great black-backed gulls and 26200 puffins, and are thus of European importance f o r both species. Years of observation are given in parentheses above.
Method to assess the relative importance oj seabird breeding colonies
163
were recognised to be of potential value for conservation on a local basis and may increase in importance should the size or composition of their breeding populations change in future. The threshold 1 ~ of the national breeding population was more frequently met by the species of seabirds studied than would have been the case, for example, in non-colonial species. None of the colonies omitted from the list of nationally important sites were considered to have been wrongly excluded.
SIZE, DIVERSITY AND RARITY Three of the remaining criteria were used together, in the next stage of analysis, to assess the value of the 133 sites listed. Size The size of the breeding population was considered to be important because of the gregarious nature of almost all seabird" species. Concentrations of nesting seabirds readily attract others. Terns prefer to breed in the vicinity of nesting gulls of small species such as black-headed gulls Larus ridibundus (e.g. Koskimies, 1957), auks nesting on a cliff attract other birds, usually non-breeding visitors (Harris, 1976; Lloyd, 1982b), and newly established gannet colonies grow mainly through immigration of breeding birds (Nelson, 1978); one in Ireland, for example, increased by 50 ~ per annum at the peak of immigration (Lloyd, 1982b). The sites were separated into three categories according to the total size of their seabird breeding populations. Broad categories were chosen deliberately to make allowance for irregularities in the census data. The thresholds of the categories had to be selected arbitrarily but the results were tested by comparison with intuitive judgements made by myself and other ornithologists. Colony size (approximate) Category A. 5000+ pairs Category B. 1000-4999 pairs Category C. 500--999 pairs.
The largest colonies (14, 10-5~o of those listed) fell into category A, 30 (22.5 ~) into category B, 25 (19 ~) into category C, and the remaining 64 (48 ~o) were too small to be categorised.
C. S. Lloyd
164
Diversity Seabird colonies naturally tend to contain at least two or three different species nesting together. It can be argued that, in conservation terms, a colony can be considered more stable if it has several different breeding species. In addition, such colonies often provide a spectacle of intrinsic merit and education potential for the public (see below). Diversity was measured by the number of breeding species most recently recorded at each seabird site. The categories of diversity were selected as before by trial and error, and checked by reference to intuition.
Colony diversity Category A. Category B. Category C.
11 or more breeding species 9 or 10 breeding species 7 or 8 breeding species.
Twenty-one seabird species regularly breed in Ireland. In addition to these, the Leach's petrel Oceanodroma leucorhoa was proved to be nesting on the Stags of Broadhaven, inaccessible stacks off the northwest of Co. Mayo, in 1982 (Irish Wildlife Conservancy, 1982). This was the first record of breeding by this species in about 70 years, and the Leach's petrel is considered to be a rare and little known nesting species. It has been omitted for the purpose of the present study. Fourteen sites (10.5 ~ of those listed) were placed in category A, 19 (14 ~ ) in category B, 29 (22 ~o) in category C, and 71 (53 ~o) were not sufficiently diverse to be categorised.
Rarity The rarity of only those species for which each site was of national importance was assessed. The reasons for this were to remove the biasing effect of casual breeding species and those present in only very small numbers. (Rare species present in small numbers were included as they were usually at or above the critical 1 ~o level.) Rarity in national and international contexts were examined separately because of the differing status of most species in each context.
National rarity. The rarity of each species on a national scale was scored from one to ten, depending on its total Irish breeding population (Table 3): < 1000 1001-5000 5001-10 000 10 001-15 000 15 001-20 000
pairs pairs pairs pairs pairs
= = = = =
10 9 8 7 6
20 001-25 000 25 001-30 000 30 001-35 000 35 001-40 000 > 40 000
pairs pairs pairs pairs pairs
= = = = =
5 4 3 2 1
Method to assess the relative importance of seabird breeding colonies
165
TABLE 3
Rarity Scores for Irish Seabirds Species
Fulmar Fulmarus glacialis Manx shearwater Puffinus puffinus Storm petrel Hydrobates pelagicus Gannet Sula bassana Cormorant Phalacrocorax carbo Shag Phalacrocorax aristotelis Black-headed gull Larus ridibundus Common gull Larus canus Lesser black-backed gull Larus fuscus Herring gull Larus argentatus Great black-backed gull Larus marinus Kittiwake Rissa tridactyla Sandwich tern Sterna sandvicensis Roseate tern Sterna dougalli Common tern Sterna hirundo Arctic tern Sterna paradisea Little tern Sterna albifrons Guillemot Uria aalge Razorbill Alca torda Black guillemot Cepphus grylle Puffin Fratercula arctica
Score for total Irish population
Score for approx. °/o N W European population
6
2
1 1
5
5 9 9 6 9 8
10 4 2 2 2 2 2
1
2
9 2 10 10 9 9 10
2 2 2 7 2 1 2
1
2
3 9 5
5 2 2
See text for sources of data and explanation of scores. However, the importance of certain species, and hence the colonies in which they nest, is under-rated using this system alone. For example, a considerable proportion of the world populations of both the storm petrel and the razorbill breed in Ireland. Both these species have large Irish populations and score only 1 and 3 respectively in Table 3. Clearly, a species' abundance on an international, as well as a national, scale is of relevance to its value in conservation terms. I n t e r n a t i o n a l rarity. The 21 species of seabirds breeding in Ireland were classed according to their abundance in northwest Europe by reference to the Irish population of each species as a proportion of the total estimated European population. The accuracy with which the latter can be estimated varies from species to species. F o r example, the total number of
166
C. S. Lloyd
gannets, which occur in only 29 breeding colonies in Europe, can be estimated far more accurately than that of black-headed gulls which breed extensively both inland throughout central Europe and on the coasts. A score for the rarity of each species on an international scale was devised with a range from one to ten (Table 3): <1~=1 1-5 ~o = 2 6-10~= 3 11--15~=4 16-20~ = 5
21-25~=6 26-30 ~ = 7 31-35~=8 36-40~ = 9 > 4 0 ~ o = 10
On this scale, the storm petrel received a score of 10 and the razorbill one of 5. Each site listed thus received two rarity scores referring to its nationally important species. The first was the sum of the species' scores on the national rarity scale, and the second the total score on the international rarity scale. Categories for these values were chosen by the same method used for the other criteria.
National rarity International rarity Category A. Category B. Category C.
32 + 25-31 18-24
14 + 10-13 6-9
Fifty-nine sites (44 ~o of those listed) were categorised for their species' rarity within Ireland, and 44 (33 ~ ) for the rarity of their species in an international context (Table 4). TABLE 4
Number of Sites in Each Species Rarity Category Category
National rarity
A B C
14 (10.5 ~o) 14(10"5~o) 31 (23~o)
International rarity 15 (11 "/~/o, 9 (7~) 20 (15~o)
Percentages are proportions of 133 listed sites.
Method to assess the relative importance o f seabird breeding colonies
167
Additional interests Seventy-five (56~o) of the 133 sites under consideration possessed additional attributes, not covered by the criteria described so far. Most of these attributes were of value in conservation terms, but Ratcliffe's (1977) recommendation was adopted that such features be considered as secondary to the intrinsic properties of the site. Additional interests included the following: (i)
Well-documented history, e.g. Saltee islands, Co. Wexford, have records for 54 of the years between 1851 and 1982. (ii) Some aspect of uniqueness in a local context, e.g. the furthest south common gull Larus canus colony (Eyeries Island, Co. Cork) or the only cliff colony in the county (Aughris Head, Co. Sligo). (iii) Site of long-term ringing study or other research, e.g. Inishglora, Co. Mayo. (iv) Educational potential or other potential for conservation, e.g. Howth Head, a colony of over 3000 seabirds within the city limits of Dublin. (v) Intrinsic appeal, e.g. Cliffs of Moher, Co. Clare. (vi) Inland colony of gulls, terns or cormorants Phalacrocorax carbo. These were once abundant in northwest Ireland but are now relatively rare. (vii) Presence of internationally important numbers of one or more species, e.g. sites listed in Table 2. (viii) Site of a gannetry; there are only four in Ireland. (ix) Diversity of non-seabird breeding species, if known (BTO Register of Ornithological Sites). Selection of key sites The final stage in this analysis was the consideration of the site assessments and the selection of nationally important key sites. The aim was to produce a listing' which could be used and relied upon by conservationists, and a hierarchical grouping, however broadly defined, was concluded to give best value to the selection. Methods used in earlier studies were examined. The selection method used by Williams (1980) to evaluate wildfowl sites was to rank indices. The index for each site was obtained from the product of values for each of the three main constituents (usage, rarity, diversity).
168
c. s. Lloyd
The final list of sites in order of rank made no allowance for the amount of difference in importance between the sites. Both Ratcliffe (1977) and Fuller (1980) avoid the use of cumulative scoring of assessment criteria but instead grade the sites, placing those of similar value together. Fuller uses five categories with different levels of importance in conservation value. These are international (A), national (B), regional (C), county (D) and local (E). (The categories A, B and C used in the present study are considered to be approximately equivalent to Fuller's B, C and D respectively.) An example of a typical final assessment of a seabird colony is given in which the site has one attribute at level A, one at level B, 2 at level D and 2 at level E. This type of assessment obscures less of the valuable information than a ranked listing, for example. However, the result is a rather loose hierarchy which cannot be interpreted so literally when making direct comparison of sites. The best selection method should be intermediate between these two. Three different ways of selecting key sites were considered in the present study. The first two used cumulative scoring which, Ratcliffe and Fuller suggest, are best suited to the comparison of sites in similar habitat. The categories (A, B and C) into which assessments of the four criteria (size, diversity, Irish rarity, international rarity) were placed were given numerical values. These were either added together (Method 1; A = 3, B = 2, C = 1) or multiplied (Method 2; A = 4, B = 3, C = 2) to give a final index value. The top four groupings obtained by method 1 contained only 7 ~o of the colonies, and the same groups arrived at by method 2 contained 1 3 ~ of the colonies. These methods were considered unsatisfactory because they produced fragmentary groupings and required additional numerical interpretation of the categories. They were rejected in favour of the third method. This method was based simply upon the number of assessment criteria which fell into category A for each colony (Table 5). Sites with four As were considered to be of major national importance as key sites, probably equivalent to Grade I sites in Ratcliffe's (1977) study. Sites with three criteria in the A category were of similar or slightly inferior merit, approximately equivalent to Ratcliffe's Grade II, and were regarded as alternatives to the four A sites. Sites with two A category attributes were recognised to be of minor national importance but high regional importance as key sites (Grade III), and those with a single A were of lower regional importance but still chosen as key sites (Grade IV). Thirtyone sites, nearly a quarter (23 ~) of those listed, were selected by this
Method to assess the relatit'e importance of seabird breeding colonies
169
TABLE 5
Selection of Key Seabird Sites Grade I: 4 As.
Grade 111:2 As.
Saltees, Co. Wexford (7) Inishnabro, Co. Kerry (5) Lambay, Co. Dublin (2)
Inishmore, Co. Galway (1) Magharee Islands, Co. Kerry (1) Inishtooskert, Co. Kerry (1) Cape Clear Island, Co. Cork (1)
Grade 11:3 As.
Grade 1V." 1 A.
Puffin Island, Co. Kerry (5) Clare Island, Co. Mayo (3) Inishtearaght, Co. Kerry (3) Grade I11:2 As.
Cliffs of Moher, Co. Clare (4) Great Skellig, Co. Kerry (4) Horn Head, Co. Donegal (3) Roaninish, Co. Donegal (3) Inishvickillaun, Co. Kerry (3) Bull Rock, Co. Cork (3) lnishglora, Co. Mayo (1) Inishturk, Co. Mayo (1)
Little Skellig, Co. Kerry (5) Lady's Island Lake, Co. Wexford (4) Illaunmaster, Co. Mayo (2) Tory Island, Co. Donegal (1) Tormore, Co. Donegal (1) Duvillaun Islands, Co. Mayo (1) Great Blasket & islets, Co. Kerry (1) Inishowen-Balbane Hds, Co. Donegal Inishmurray, Co. Sligo Benwee Head, Co. Mayo Inishkea Islands, Co. Mayo Scariff, Co. Kerry Kenmare Bay, Co. Kerry
Figures in brackets refer to number of additional interesting features associated with each site; see text for details. In direct comparison of sites, attributes in categories B and C should also be taken into account.
method. Although categories B and C played no part in the choice of key sites, they were useful for direct comparison of sites.
CONCLUSIONS Both Ratcliffe (1977) and Fuller (1980) stress that site assessment and selection should be preceded by the implementation of a strict policy for site boundary demarcation. Otherwise the quality of a site could reflect the extent and diversity of its area. This is as relevant to seabird sites as it was to the wider range of sites examined by these authors, and it is one way in which the present study could have been improved, had the necessary data been available. The procedure described here for site assessment and selection can be used with few modifications to examine the importance of seabird
170
C. S. Lloyd
colonies outside Ireland, given a knowledge of the estimated total breeding populations of each species on a national and northwest European (or other suitable biogeographic) scale. To summarise, the basic steps are as follows: 1. 2. 3. 4. 5. 6a 7. 8. 9.
Calculation of 1 ~o national and international population levels. Selection of colonies with one or more species at the national level of abundance or above. Obtain approximate total number of regularly/recently breeding birds at each site. Obtain number of regularly/recently breeding species for each site. Devise scoring system for rarity of each species on (a) national scale, and (b) international scale. & 6b. Calculation of total rarity score, on each scale, for species breeding in nationally important numbers at each site !(see 2). List additional features of interest/conservation value at each site. Derive suitable limits to categories A, B and C for the attributes in 3, 4, 6a and 6b above. Selection of key colonies, with 4 As, 3 As, 2 As and 1 A, and grade accordingly.
The relative importance of different seabird colonies is a dynamic property. It is essential that an up-to-date seabird inventory be maintained for Irish colonies so that re-assessment can be made on a regular, if not annual, basis. New data on breeding numbers will become available for individual colonies, for the Irish populations of each species, and for northwest European populations. Meanwhile, plans for the creation of specially protected areas, the purchase of land for reserves, the development of sites with educational potential and other measures for seabird conservation in Ireland can take into account the existence of colonies which have been identified by this study as being of key national importance.
ACKNOWLEDGEMENTS I am grateful to the Forest & Wildlife Service of the Department of Forestry & Fisheries, Dublin, who provided the funding for this study, and to Oscar Merne who gave valuable advice and encouragement through his supervision. The manuscript of this paper was improved by
Method to assess the relative importance of seabird breeding colonies
171
comments from R. J. Fuller, an a n o n y m o u s referee, and Dr M. P. Harris. Unpublished information was m a d e available to me for the breeding seabird inventory by Dr D. Cabot, M. O'Meara, Dr A. Whilde, Dr K. Partridge, H. Brazier, O. J. Merne and Dr G. J. Thomas.
REFERENCES Atkinson-Willes, G. L. (1976). The numerical distribution of ducks, swans and coots as a guide in assessing the importance of wetlands in winter. Proc. int. ConJl on Conservation of Wetlands and WaterJowl, Heiligenhafen, 1974, ed. by M. Smart, 199-254. Bullock, I. D. & Gomersall, R. (1981). The breeding populations of terns in Orkney and Shetland in 1980. Bird Study, 28, 187-200. Cramp, S., Bourne, W. R. P. & Saunders, D. (1974). The seabirds of Britain and Ireland. London, Collins. Evans, P. G. H. & Birkhead, T. R. (1982). Editorial. Seabird Report, 6, 3-4. Fuller, R. J. (1980). A method for assessing the ornithological interest of sites for conservation. Biol. Conserv., 17, 229-39. Harris, M. P. (1976). Inter-colony movements of Farne Islands puffins. Trans. nat. Hist. Soc. Northumb., 42, 115-18. Hutchinson, C. D. (1979). Ireland's wetlands and their birds. Dublin, Irish Wildbird Conservancy. Irish Wildbird Conservancy. (1982). Leach's petrels in Co. Mayo. IWC News, No. 33, 3. Koskimies, J. (1957). Terns and gulls as features of habitat recognition for birds nesting in colonies. Orn. Fenn., 34, 1-6. Lloyd, C. S. (1982a). An inventory Q['seabird breeding colonies in the Republic oj Ireland. Unpublished data and report, Forest & Wildlife Service, Dublin. Lloyd, C. S. (1982b). The seabirds of Great Saltee. Irish Birds, 2, 1-37. Nelson, B. (1978). The Gannet. Berkhamsted, T. & A. D. Poyser. Osieck, E. R. & M6rzer Bruyns, M. F. (1981). Important bird areas in the European community. Unpublished report prepared by the International Council for Bird Preservation, Cambridge, for the Environment & Consumer Protection Service of the Commission of the European Communities. Ratcliffe, D. A. (ed.). (1977). A nature conservation rev&w, 1. Cambridge, Cambridge University Press. Scott, D. D. (1980). Contribution to the determination of special protection areas Jbr the conservation of birds. Unpublished report prepared by the International Wildfowl Research Bureau, Slimbridge, for the Environment & Consumer Protection Service of the Commission of the European Communities. Seabird Group (1980). The auk censusing manual, Sheffield, England.
172
C. S. Lloyd
Thomas, G. J. (1982). Breeding terns in Britain and Ireland, 1975-79. Seabird Report, 6, 59-69. Whilde, A. (1978). A survey of gulls breeding inland in the west of Ireland in 1977 and 1978 and a review of the inland breeding habit in Ireland and Britain. Irish Birds, 1, 134-60. Williams, G. (1980). An index for the ranking of wildfowl habitats, as applied to eleven sites in west Surrey, England. Biol. Conserv., 18, 93-9.