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Island releases of saddlebacks Philesturnus carunculatus in New Zealand
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S0006-3207(96)00006-7
Biological Conservation 77 (1996) 151 15"7 Copyright @ 1996 Elsevier Science Limited Printed in Great Britain. All rights reserved 0006-3207,/96/$15.00+0.0(!
ISLAND RELEASES OF SADDLEBACKS Philesturnus carunculatus IN NEW Z E A L A N D Tim G. Lovegrove* 47 Pupuke Road, Birkenhead, Auckland 10, New Zealand
(Received 12 October 1994; accepted 20 October 1995)
Abstract The success of 45 releases of saddlebacks Philesturnus carunculatus between islands in New Zealand is compared. Forty-three releases were 'immediate' (birds released immediately on arrival at site), and two were 'delayed' (birds released after 12 days' conditioning in an aviary on site). Most releases with a balanced sex ratio on predator-J?ee islands were successful. Others failed because (1) predators were still present, or arrived after release, or (2) too few birds were released. The success of releases may have been enhanced by the birds' limited dispersal, small territories, flocking behaviour, high reproductive rate and broad habitat requirements. Before one release, prior conditioning of the bird~ in an aviary on site did not improve their subsequent survival. Immediate releases shouM be used for wildcaught birds, and the captive period minimised. Conditioning may be appropriate for captive-reared birds" to adjust to the wild. Copyright © 1996 Elsevier Science Ltd
Petroica traversi (Merton, 1990; Reed & Merton, 1991; Butler & Merton, 1992), saddleback releases have outnumbered those of all other small New Zealand forest birds; most of the techniques now used for such birds were tested and refined using saddlebacks (Lovegrove & Veitch, 1994). Like some other New Zealand forest birds (Flack, 1978), saddlebacks are particularly suitable for releases because they have: (1) limited dispersal and are sedentary; (2) flocking behaviour which may facilitate pair formation; (3) small territories, e.g. < 0.4 ha on Cuvier (Lovegrove & O'Callaghan, 1982), which allow large populations on small islands, e.g. 75 birds on < 20 ha (Big I), and 1000 birds on < 150 ha (Cuvier); (4) broad habitat requirements, from shrubland to tall forest; (5) a high reproductive rate. Although saddlebacks have a low reproductive rate in stable long-established populations, they are capable of a high reproductive rate where there is little intraspecific competition (T. G. L., unpublished data). A high reproductive rate allows rapid population expansion and maintenance of genetic variability (Nei et al., 1975). These features are important in many species which colonise islands naturally (Lack, 1976: Fyfe, 1978; Diamond, 1985). Although many immediate releases (Scott & Carpenter, 1987) of saddlebacks after 1960 were successful, high mortality during the first year prevailed on some islands, e.g. Little Barrier and Motukawanui, where respectively only 22 of 50 and eight of 16 birds survived a year after release, and Kapiti where only 13 of 43 were alive 2 months after release in 1987. An experimental delayed release was made in 1988 in the hope that this might result in better survival during pair formation and territory establishment, when losses are usually high (T. G. L., unpublished data). Greater survival of founding birds may improve genetic variability of the survivors (Frankel & Soul& 1981; Shaffer, 1987). Releases have become important for conserving many endangered species, but there is need for further work on the factors affecting success (Fyfe, 1978; Scott & Carpenter, 1987; Griffith et al., 1989; Short et al., 1992: Armstrong & Craig, 1995; Armstrong, 1995). Here I review the outcome of all saddleback releases
Keywords." New Zealand, saddleback, translocation, release methods.
INTRODUCTION Releases of endangered birds in New Zealand have resulted in many populations being established in new or restored island communities (Williams, 1977; Merton, 1975; Atkinson, 1990; Craig, 1990). These have averted the extinction of several taxa, including little spotted kiwi Apteryx owenii, buff weka Gallirallus australis hectori, and South Island saddleback Philesturnus c. carunculatus; the last species was rescued when ship rats Rattus rattus invaded its only remaining habitat (Atkinson & Bell, 1973). The release of North Island saddlebacks P. c. rufusater on Cuvier Island in 1968 may have been the first in which wild birds were re-established where they had been previously extirpated (Merton, 1975; Fyfe, 1978). Conservation of saddlebacks has depended on island releases, because they cannot coexist with carnivores introduced to mainland New Zealand since 1770 (King, 1984). With the possible exception of Chatham Island black robins *Tel.: (64) 9 4806587. 151
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since 1925, and examine the results of immediate and delayed releases on Kapiti Island in 1988. METHODS
Data for this review were derived from Merton (1975), Nillson (1978), Atkinson (1990), Roberts (1991), unpublished reports of the New Zealand Wildlife Service (pre-1987) and of the Department of Conservation (post-1987), and my own knowledge through participating in most North Island saddleback releases since 1977. The immediate and delayed releases on Kapiti in 1988 were similar to others (Lovegrove & Veitch, 1994). On arrival at Kapiti, 20 saddlebacks were released immediately near a 5 × 3 x 2 m aviary, where the remaining 19 birds were held for 12 days before release. (Ideally the two groups should have been released simultaneously, but the costs of multiple trips to remote islands to capture the birds, and other logistical constraints, precluded this.) In captivity a maintenance diet was provided and supplementary food consisting of nectar mix and bird buns (Lovegrove & Veitch, 1994) was available ad lib. near the aviary for all birds after release; this food was replenished daily for 8 weeks, then less frequently until feeding was stopped 12 weeks later. Both releases coincided with an experiment comparing the survival of birds using ratproof (against Rattus norvegicus) roost boxes with those using natural roosts (Lovegrove, 1992). To compensate for the possible differential survival after release, the two groups were split evenly between those released immediately and those with delayed release. RESULTS Review of all releases
Forty-five saddleback releases between 1925 and 1994 included 28 of P. c. rufusater to 11 different islands and 17 of P. c. carunculatus to 13 islands (Table 1). Releases of P. c. rufusater totalled 846 birds, with a mean of 30 per release (SD 13.8, range 6-50); while P. c. carunculatus totalled 464, with a mean of 27 per release (SD 12.l, range 15-59). All but the 1988 and 1989 releases to Kapiti Island were immediate. The two delayed releases were both on Kapiti; they included the release described here, and an experimental release in 1989 testing the effects of familiarity (Armstrong et al., 1994). Some of the source islands have been very productive, and many birds have been removed without adverse effect. The most remarkable was Big Island (20 ha) from which 151 South Island saddlebacks were removed between 1969 and 1978. During this period the mean population at any one time was about 75 birds (Nillson, 1978). In order of importance, the main source islands and numbers removed for North Island saddlebacks have been Cuvier (373), Hen (205) and
Stanley (122); all of these have much larger populations than Big Island (e.g. Cuvier c.1000, Hen c.500 and Stanley c.250). The maximum number of birds removed in any one year was 74 from Cuvier in 1984. Success or failure
I have regarded as successful those releases which produced self-sustaining populations. Eleven of 28 releases of North Island saddlebacks and 10 of 17 releases of South Island saddlebacks were successful. The success rate is higher when analysed on a per island basis because some islands, including unsuccessful ones, had more than one release. The success rate was similar for northern and southern islands on a per island basis, eight of 11 and 10 of 13 respectively. Successful islands had forests ranging in area from 6 ha (Betsy) to over 3000 ha (Little Barrier), and had either Polynesian rats R. exulans or mice Mus musculus as the only rodents (all northern islands), or lacked them entirely (all southern islands). Three successful southern islands (Kundy, Motunui, and Jacky Lee), and one northern one (Mokoia) also had weka Gallirallus australis, a flightless omnivorous rail which sometimes preys on saddleback fledglings (T. G. L., unpublished data). There was a significant relationship between a lack of important predators on islands (i.e. feral cats Felis catus, European rats R. rattus and R. norvegicus, Polynesian rats (from South Island offshore islands only) and stoats Mustela erminea), and the success of translocations (X2~=22-2, p <0.001). Although saddlebacks on islands with wekas did not do as well as those on weka-free islands, surveys indicate that they coexisted: moreover there were sufficient saddlebacks on Kundy Island for birds to be removed in 1980 and 1982. Wekas were removed from Kundy between 1981 and 1985 (Veitch & Bell, 1990), and saddlebacks apparently increased (Roberts, 1991). Two factors appear to be related to the failure of some saddleback releases. (1) The presence of predators, or their arrival after the birds were released. All releases (n=12) of North Island saddlebacks failed on islands with either feral cats (Little Barrier), or a combination of Norway rats R. norvegicus, wekas and feral cats, or Norway rats and wekas (Kapiti) (Turbott, 1947; Wilkinson & Wilkinson, 1952: Lovegrove, 1992). By contrast 10 out of 13 releases of North Island saddlebacks were successful on islands where R. exulans was the only rat (Merton, 1975; T. G. L., unpublished data). All releases (n--5) of South Island saddlebacks onto islands with either R. exulans and wekas (Chetwode), or R. exulans (Putauhinu), have respectively failed or have ailing populations (Nillson, 1978: Roberts, 1991). On Chetwode a combination of R, exulans and wekas may have been detrimental because saddlebacks have coexisted with wekas on Big South Cape, Kundy, Motunui, and Jacky Lee; and with wekas and mice on Mokoia in the absence of rats. On Motukawanui and Maud Islands saddlebacks were
Island releases of saddlebacks in New Zealand
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Table 1. Summary of saddlebaek translocations to islands 1925-1995 (a) N o r t h Island saddleback Date of release
Source island
Release island
Possible predators
Area No. Result (ha) released
Notes, population size
References
18 Oct 1925 29 Oct 1925 12 Jun 1950 Jan 1964 30 Jan 1966 25 Jan 1968 5 Feb 1968 Mar 1971 23 Jan 1977 20 Jan 1981 6 Feb 1981 12 Feb 1981 19 Feb 1982 3 Mar 1982 10 Mar 1982 Feb 1983 19 Mar 1983 25 Feb 1984 26 Feb 1984 17 Mar 1984 3 Mar I985 10 Oct 1986 6 Mar 1987 18 Apr 1988 26 Sep 1987 24 Aug 1988 26 Aug 1989 12 Apr 1992
Hen Hen Hen Hen Hen Hen Hen Whatupuke Cuvier Hen Cuvier Chickens Hen Cuvier Chickens Hen Cuvier Cuvier Cuvier Hen Cuvier Chickens Cuvier Cuvier Stanley Stanley Stanley Tiritiri
Little Barrier Kapiti Lady Alice Whatupuke Red Mercury Cuvier Fanal Lady Alice Stanley Kapiti Kapiti Kapiti Kapiti Kapiti Kapiti Motukawanui Kapiti Little Barrier Tiritiri Motukawanui Fanal Little Barrier Little Barrier Little Barrier Kapiti Kapiti Kapiti Mokoia
C,K C,N,K,P,W K K K K K K K N,K,P,W N,K,P,W N,K,P,W N,K,P,W N,K,P,W N,K,P,W K N,K,P,W K K K K K K K N,K,W N,K,W N,K,W M,W
3083 1965 155 102 225 170 75 155 100 1965 1965 1965 1965 1965 1965 380 1965 3083 197 380 75 3083 3083 3083 1965 1965 1965 135
Disappeared quickly Survived till March 1931 3 birds, December 1952 c.500 * c.400 * c.1000 * c.5 in 1973 c.300 in 1986 * c.250 1986-89 * Gone by 1985 1 survivor Nov 1991 Gone by 1985 1 survivor Nov 1991 1 survivor 1985 1 survivor 1985 Gone by Aug 1986 # 2 survivors 1985 c.1500 by 1995 * c.200 by 1991 * Gone by Aug 1986 # c.5 survivors 1987 c. 1500 by 1995 * c.1500 by 1995 * c.1500by 1995 * 7 survivors Nov 1991 + 8 survivors Nov 199l + 5 survivors Nov 1991 + c. 140 by Sep 1994
Turbott, 1947 Wilkinson & Wilkinson, 1952 Chambers et al., 1955 Merton, 1965 Merton, 1975 Merton, 1975; Jenkins, 1978 P. F. Jenkins, pers. comm. T. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data Y. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data Y. G. L. unpublished data Craig, 1990 T. G. L. unpublished data C. Hodsell, pets. comm. T. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data Y. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data P. Jansen, pers. comm.
Area No. Result (ha) released
Notes, population size
References
9 9 6 23 29 29 25 21 24 25 50 25 22 50 22 16 50 50 24 12 29 42 47 49 43 39 40 36
x x x s s s x s s x x x x x x x x s s x x s s s x x x s
(b) South Island saddleback Date
Source island
Release island
Possible predators
31 Aug 1964 31 Aug 1964 14 Jul 1965 2 Aug t970 Mar 1969 5 Mar 1972
Big South Cape Big South Cape Big South Cape Big Big Big, Kaimohu, and Betsy Big Big Kundy Big, Kaimohu Big, Kaimobu Big, Kaimohu Big, Kaimohu Big, Kundy Big, Kundy North, Jacky Lee
Big Kaimohu Inner Chetwode Inner Chetwode Betsy North and Womens Putauhinu Putauhinu Putauhinu Kundy Maud Maud Motunui Jacky Lee Breaksea Motuara
Nil Nil K,W K,W Nil Nil Nil K K K W Nil Nil W Nil Nil Nil
6 Mar 1974 25 Jan 1976 Feb 1 9 8 4 31 Jan 1978 Jan 1980 Feb 1982 Feb 1981 Feb 1986 Mar 1992 5 Mar 1994
23 11 195 195 6 8 8 141 141 141 19 309 309 48 30 170 59
21 15 30 17 16 19 20 23 22 20 38 34 38 20 46 59 26
s s x x x s s u u u s x x s s s s
c.80 1986 Roberts, 1991 c.30 1978 Nilsson, 1978 Gone by 1973 Merton, 1975 Gone by 1973 Merton, 1975 c.12 May 1978 Nilsson, 1978 c.30 in 1988 Roberts, 1991 c.25 in 1988 Roberts, 1991 c.20 in 1991 Roberts, 1991 c.20 in 199l Roberts. 1991 c.20 in 1991 Roberts, 1991 c.80 1986 Roberts, 1991 Gone by 1983 # Roberts, 1991: Bell, 1983 Gone by 1983 # Roberts, 1991; Bell, 1983 c.60 1991 Roberts, 1991 c.65 1991 Roberts, 1991 30+ survivors March 1993 Rasch & McClelland, 1993 c.30 survivors March 1995 W. Cash. pets. comm.
* Estimate of population based on area of island and habitat quality, transect counts (Cuvier), or time since release (Little Barrier). s Successful translocation (i.e. self-sustaining population). x Failed translocation. u Outcome uncertain (Putauhinu Island, where Polynesian rats have apparently reduced saddleback survival and breeding success). # Stoats invaded Motukawanui Island in about 1985, and Maud Island in 1982. + Survival on Kapiti Island enhanced by addition of roost and nest boxes, but population gradually declining. C, feral cat; K, kiore (Polynesian rat); N, Norway rat; M, mice; P, Australian possum; W, weka. (Note: Australian possums removed from Kapiti Island by 1986, and Polynesian rats removed from Stanley, Red Mercury, Cuvier, Whatupuke and Tiritiri Islands between 1991 and 1994.)
w i p e d o u t a f t e r s t o a t s i n v a d e d (Bell, 1983; T. G . L.,
released. In 1953 p o s s i b l y o n l y t h r e e r e m a i n e d ( C h a m b e r s
u n p u b l i s h e d d a t a ) . N o r t h I s l a n d s a d d l e b a c k s b r e d succ e s s f u l l y o n M o t u k a w a n u i in t h e p r e s e n c e o f R. exulans
et al., 1955). A r e l e a s e o f 21 b i r d s o n t h e s a m e i s l a n d in 1971 s u c c e e d e d .
b e f o r e s t o a t s r e a c h e d t h e i s l a n d (T. G , L. u n p u b l i s h e d
T w o r e l e a s e s o n F a n a l I s l a n d (1968, 1985) f a i l e d f o r
d a t a ) . (2) T o o f e w b i r d s t r a n s l o c a t e d . I n 1950 o n L a d y A l i c e I s l a n d o n l y six b i r d s ( u n k n o w n sex r a t i o ) w e r e
u n k n o w n r e a s o n s . F a n a l (75 h a ) w a s t h e s m a l l e s t i s l a n d where
North
Island
saddlebacks were
released, and
T. G. Lovegrove
154
R. exulans was the only mammal known to be present. Fanal is bigger than many southern islands with successful saddleback populations, and a similar size to Coppermine Island (80 ha), which North Island saddlebacks colonised naturally by flying a 150 m strait from Whatupuke Island (Newman, 1980). Results of immediate and delayed releases in 1988 Although there was no objective measure (by weighing) of the condition of the birds at the time of release all appeared to be healthy, and all fed well in captivity. The birds were not recaptured and weighed before release because the extra handling is stressful. In previous years saddlebacks had an average weight gain of 2.5% after a period in captivity (Lovegrove & Veitch, 1994). After 2 months (by which time most birds had settled and paired), 12 of 20 of the birds released immediately and 15 of 19 of the birds with delayed release were still alive. The difference in survival after two months was not significant (A~1=1-64, p >0-1), and similar numbers of the two groups survived after 1 year. Survivorship of the two groups of birds during the first year is shown in Fig. 1. After release the supplementary food was used by 50% of the birds released immediately and all of the birds in the delayed release. Their survival was not significantly different (X2,=0.93 p >0-1). DISCUSSION Immediate releases of saddlebacks were usually successful so long as the release islands lacked important predators. Successful release islands lacked predators totally (some Stewart Island outliers); or had wekas only (Kundy, Motunui, Jacky Lee); or had mice and wekas (Mokoia); or had R. exulans only (Red Mercury, Cuvier, Whatupuke, Lady Alice, Stanley, Little Barrier, and Tiritiri). 90
---o--- Immediate
7~001 \
~'~,x
•
release
Delayed release
,o
3020100
0
l
i
I
I
1
2
3
4 5 6 7 8 Months since release
l
i
i
i
i
;
i
I
9
1
11
12
Fig. t. Survival of North Island saddlebacks during the first year after immediate (20 birds) and delayed releases (19 birds) in 1988 on Kapiti Island, New Zealand. There was no significant difference in survival after the 2-month territory and pair formation phase, and similar numbers of the two groups survived after 1 year.
All releases on islands lacking important predators where more than 15 birds were released were successful. The release of six birds on Lady Alice in 1950 failed probably because there were too few; a subsequent release of 21 birds succeeded, Surveys showed that half of the birds in some releases failed to survive the first year (T. G. L., unpublished data). If such a decline occurred after the first release on Lady Alice then the tiny population would have been vulnerable. Although that release of six failed, two experimental releases of five South Island robins Petroica australis, and one of seven Chatham Island black robins, succeeded (Flack, 1978; Morris, 1977; Butler & Merton, 1992). Releases of as few as nine saddlebacks might succeed in good habitat, provided the sex ratio is reasonably balanced. A release of nine on Kapiti in 1925 resulted in successful breeding at least until 1931 (Wilkinson and Wilkinson, 1952). The population probably died out as a result of the combined effects of predation by Norway rats, which were found to be important predators of the saddlebacks released on Kapiti between 1981 and 1989 (Lovegrove, 1992); feral cats which were not eradicated from Kapiti until 1934 (Veitch & Bell, 1990); and possibly wekas which may have preyed on some young. Cats have been blamed for the extinction of saddlebacks on Little Barrier last century; and for the demise of birds released in 1925 (Turbott, 1947). These early failures were mainly due to ignorance of the possible effects of predators. Apart from the experimental releases on Kapiti during the 1980s (undertaken because coexistence with R. norvegicus was thought possible), recent releases have all been to islands lacking important predators where the success rate has been high. Since 1964 the aim in saddleback releases has been to move 2 0 4 0 birds, although more were released on some big islands such as Little Barrier, or where experimental programmes were conducted such as on Kapiti. These have been facilitated by improved capture techniques (Merton, 1975), A review of translocations (Griffith et al., 1989) shows that releases of about 40 birds into good habitat will probably be successful, and that releases of more than 80-120 birds do little to increase success. A study of New Zealand translocations (J. g. Craig & C. Reed, pers. comm.) shows no relationship between success and number of birds in releases of five to 366 birds; releases of as few as five birds on predator-free islands are likely to succeed. Inadequate restoration of communities is a continuing problem on Kapiti and Putauhinu Islands. Recent attempts to enhance survival on Kapiti by releasing birds that use roost boxes and providing roost and nest boxes have greatly reduced the level of Norway rat predation; but population modelling suggests that saddlebacks will gradually decline over a 50-70 year period (Lovegrove, 1992). On Putauhinu Island South Island saddlebacks have not thrived as on nearby rodent-free
Island releases o f saddlebacks in New Zealand islands. All birds in the southern populations are derived from previously rodent-free Big South Cape Island. Unlike the North Island subspecies, the South Island birds may be unable to coexist with R. exulans, and in order to survive the population on Putauhinu may need roost and nest boxes, or eradication of R. exulans. The failure of saddlebacks to establish on Inner Chetwode Island has been blamed on wekas, which were numerous and may have preyed on saddlebacks visiting one of the few available water supplies (Merton, 1975). However P. c. carunculatus coexists with weka on several much smaller Stewart Island offliers; and since the population on Putauhinu has struggled to coexist with R. exulans, the presence of this rat on Chetwode (perhaps combined with the effects of wekas) may have been the limiting factor. Saddleback translocations to Maud and Motukawanui Islands should never have been undertaken, because even then stoats were already known to have reached such islands up to 1100 m offshore in New Zealand (Taylor & Tilley, 1984). Any island within 1200 m of the mainland is at risk, although closer islands (e.g. Breaksea) may be secure if they are very exposed (Taylor & Tilley, 1984). Islands for future saddleback releases must be carefully chosen with respect to their risk of stoat invasion. The immediate and delayed releases on Kapiti suggest that little was gained by first conditioning the birds; but this result is based on only one test; more replicates are needed. A single release of stitchbirds Notiomystis cincta using the same methods in 1991 suggested that birds that were released immediately survived better than delayed release birds (Castro et al., 1994a). Griffith et al. 's (1989) review of translocations showed that high-quality habitat at the release site is probably the most important prerequisite. Delayed releases are labour-intensive and costly, and captivity is probably stressful; foods for a maintenance diet may also be unsuitable, time-consuming or difficult to obtain, and there is increased risk of injury or disease (Reed & Stockdale, 1994). Wild-caught birds should be released as soon as possible. Where capture and release points are close together, and where catching is efficient and transport fast, birds may be caught and released within a few hours. This may be the best technique for small insectivores that are difficult to feed. Usually releases are at distant sites, and it may take several days to catch sufficient birds, so a holding aviary is needed near the capture site. The period in captivity should be used to accustom birds to artificial foods that will sustain them during transport, especially if delays are expected (Lovegrove & Veitch, 1994). Supplementary feeding after release may not be necessary for saddlebacks, but stitchbirds on Kapiti depended heavily on supplementary food after release, especially during spring; and one feeder was maintained permanently (Castro et al., 1994b). These differences emphasise the need for trials
155
(with related species if possible) to refine techniques before an endangered species is released. The transfers of Chatham Island black robins benefited from the knowledge that as few as five South Island robins could be released successfully (Flack, 1978); and recent transfers of small numbers of yellowheads Mohoua ochrocephala (Dilks et al., 1994) will assist future operations with this species. Delayed releases should be used where birds are captive-bred or where they have had a long stay in captivity. These birds usually need conditioning to adjust" to life in the wild (Temple, 1978a; Berger, 1978; Cade, 1990; Cade & Jones, 1992; Jones et al., 1992). Delayed releases may also be appropriate for migratory species, or those likely to disperse far from the release point (Temple, 1978b), although recent work suggests that the needs of some species may be complex (Akcakaya, 1990; Franzreb, 1990). Delayed releases have also proved successful for captive-reared flocking species such as game birds (Ellis et al., 1978).
ACKNOWLEDGEMENTS Funding for this study was provided by the New Zealand Department of Conservation, the former Department of Lands and Survey, the New Zealand Lottery Grants Board and the University of Auckland Research Committee. I thank the University of Auckland School of Biological Sciences for institutional support, and the Department of Conservation for permission to work on the island reserves. I also wish to thank John Craig, Jared Diamond, Peter Jenkins, Henrik Moller, Ron Moorhouse, Craig Miller, Dick Sibson, Dick Veitch and two anonymous referees for useful comments.
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Bell, B. D. (1983). The challenge of the stoat invasion on Maud Island. Forest and Bird, 227, 12-14. Berger, A. J. (1978). Reintroduction of Hawaiian Geese. In Endangered birds: management techniques for preserving threatened species, ed. S. A. Temple. Madison University, Wisconsin Press, Madison, WI, pp. 339~t4. Butler, D. & Merton, D. (1992). The black robin: saving the worM's most endangered bird. Oxford University Press, Auckland. Cade, T. (1990). Extirpation and re-establishment of the peregrine in eastern United States, Abstract No. 726. Acta XX Congressus Internationalis Ornithologici, Christchurch, New Zealand, 1990. Cade, T. J. & Jones, C. G. (1992). Progress in restoration of the Mauritius Kestrel. Conserv. Biol., 7(1), 169-75. Castro, I., Alley, J. C., Empson, R. A. & Minot, E. O. (1994a). Translocation of Hihi or Stitchbird Notiomystis cincta to Kapiti Island, New Zealand: transfer techniques and comparison of release strategies. In Reintroduction biology of Australian and New Zealand fauna, ed. M. Serena. Surrey Beatty & Sons, Chipping Norton, pp. 113-30. Castro, I., Minot, E. O. & Alley, J. C. (1994b). Feeding and breeding behaviour of Hihi or Stitchbirds Notiomystis cincta recently transferred to Kapiti Island, New Zealand, and possible management alternatives. In Reintroduction biology of Australian and New Zealand fauna, ed. M. Serena. Surrey Beatty & Sons, Chipping Norton, pp. 121-8. Chambers, B. S., Chambers, S. & Sibson, R. B. (1955). Notes on the Hen and Chicken Islands. Notornis, 6, 152 7. Craig, J. L. (1990). Islands: Refuges for threatened species. Forest and Bird, 21(3), 28-9. Diamond, J. M. (1985). Population processes in island birds: Immigration, extinction and fluctuations. In Conservation of island birds, ed. P. J. Moors. ICBP Tech. Publ., No. 3: 17-21. Dilks, P., Elliott, G. & O'Donnell, C. (1994). Transfer of Mohua to Centre Island, Lake Te Anau. Ecol. Manag., 2, 17 22. Threatened Species Unit, N. Z. Department of Conservation. Ellis, D. H., Dobrott, S. J. & Goodwin, J. G. (1978). Reintroduction techniques for masked bobwhites. In Endangered birds'." Management techniques .,for preserving threatened species, ed. S. A. Temple. Madison University, Wisconsin Press, Madison, WI, pp. 345-53. Flack, J. A. D. (1978). Interisland transfers of New Zealand black robins. In Endangered birds'." Management techniques" for preserving threatened species, ed. S. A. Temple. Madison University, Wisconsin Press, Madison, WI, pp. 365-72. Frankel, O. H. & Soul& M. E. (1981). Conservation and evolution. Cambridge University Press, Cambridge. Franzreb, K. E. (1990). An analysis of options for reintroducing a migratory native passerine, the endangered least bell's vireo Vireo bellii pusillus in the Central Valley, California. Biol. Conserv., 53, 105-23. Fyfe, R. W. (1978). Reintroducing endangered birds into the wild a review. In Endangered birds: management techniques for preserving threatened species, ed. S. A. Temple. Madison University, Wisconsin Press, Madison, WI, pp. 323-9. Griffith, B., Scott, J. M., Carpenter, J. W. & Reed, C. (1989). Translocation as a species conservation tool: status and strategy. Science, N.Y., 245, 477-80, Jenkins, P. F. (1978). Cultural transmission of song patterns and dialect development in a free-living bird population. Anim. Behav., 26, 50-78. Jones, C. G., Swinnerton, K. S., Taylor, C. J. & Mungroo, Y. (1992). The release of captive-bred pink pigeons Columba mayeri in native forest on Mauritius. A progress report July 1987-June 1992. Dodo, J. Wildl. Preserv. Trusts 28, 92-125.
King, C. M. (1984). Immigrant killers. Oxford University Press, Auckland. Lack, D. (1976). Island biology illustrated by the land birds of Jamaica. Blackwell Scientific Publications, Oxford. Lovegrove, T. G. (1992). The effects of introduced predators on the saddleback Philesturnus carunculatus, and implications for management. PhD Thesis, University of Auckland, New Zealand. Lovegrove, T. G. & O'Callaghan, A. P. (1982). Recent studies of the North Island saddleback on Cuvier Island. Forest and Bird, 14(1), 26-30. Lovegrove, T. G. & Veitch, C. R. (1994). Translocating wild forest birds, Ecol. Manag., 2, 23-35. Threatened Species Unit, N. Z. Department of Conservation, Wellington. Merton, D. V. (1965). Transfer of saddlebacks from Hen Island to Middle Chicken Island, January 1964. Notornis, 12, 213-22. Merton, D. V. (1975). The saddleback: its status and conservation. In Breeding endangered species in captivity, ed. R. D. Martin. Academic Press, London, pp. 61-74. Merton, D. V. (1990). The Chatham Island black robin. Forest and Bird, 21(3), 14-19. Morris, R. B. (1977). Black robin transfers. Wildlife - A review, No. 8, 44-8. Nei, M., Maruyama, T. & Chakraborty, R. (1975). The bottleneck effect and genetic variability in populations. Evolution, 29, 1-10. Newman, D. G. (1980). Colonisation of Coppermine Island by the North Island saddleback. Notornis, 27, 146 7. Nillson, R. J. (1978). The South Island saddleback. Wildlife - - A Review, No. 9, 32-6. Rasch, G. & McClelland, P. (1993). South Island saddlebacks transferred to Breaksea Island. Notornis, 40, 22%31. Reed, C. & Merton, D. V. (1991). Behavioural manipulation of New Zealand endangered birds as an aid towards species recovery. Acta XX Congressus Internationalis Ornithologici, 2514-22. Reed, C. E. M. & Stockdale, P. H. G. (1994). Disease considerations in captive breeding and translocations of New Zealand birds. Ecol. Manag., 2, 46-54. Threatened Species Unit, N. Z. Department of Conservation, Wellington. Roberts, A. (1991). A recovery plan Jor the South Island saddleback. N. Z. Departmerlt of Conservation, Southland Conservancy. Private Bags, Invercargill, New Zealand. Scott, M. J. & Carpenter, J. W. (1987). Release of captivereared or translocated endangered birds: What do we need to know? The Auk, 104, 544-5. Shaffer, M. (1987). Minimum viable populations: coping with uncertainty. In Viable populations .for conservation, ed. M. E. Soul6. Cambridge University Press, Cambridge, pp. 69-86. Short, J., Bradshaw, S. D., Giles, J., Prince, R. I. T. & Wilson, G. R. (1992). Reintroduction of macropods (Marsupalia: Macropodoidea) in Australia a review. Biol. Conserv., 62, 189-204. Taylor, R. H. & Tilley, J. A. V. (1984). Stoats (Mustela erminea) on Adele and Fisherman Islands, Abel Tasman National Park, and other offshore islands in New Zealand. N. Z. J. Ecol., 7, 139~,5, Temple, S. A. (1978a). Manipulating behavioural patterns of endangered birds. A potential management technique. In Endangered birds: management techniques for preserving threatened species, ed. S. A. Temple. Madison University, Wisconsin Press, Madison, WI, pp. 43543. Temple, S. A. (1978b). Reintroducing birds of prey into the wild. In Endangered birds: management techniques for preserving threatened species, ed. S. A. Temple. Madison University, Wisconsin Press, Madison, WI, pp. 355-63.
Island releases o f saddlebacks in New Zealand Turbott, E. G. (1947). Birds of Little Barrier Island. N. Z. Bird Notes, 2(5), 92-108. Veitch, C. R. & Bell, B. D. (1990). Eradication of introduced animals from the islands of New Zealand. In Ecological restoration of New Zealand islands, ed. D. R. Towns; C. H. Daugherty & I. A. E. Atkinson. N. Z. Conservation Sciences Publication, No. 2. Dept. of Conservation, Welling-
157
ton, pp. 137-46. Wilkinson, A. & Wilkinson, A. (1952). Kapiti Island Sanctuary. Published for the editor, R. W. D. Stidolph by the Masterton Printing Company Ltd., Masterton, New Zealand. Williams, G. R. (1977). Marooning - - a technique for saving threatened species from extinction. International Zoo Yearbook, 17, 102-6.
PII:
S0006-3207(96)00006-7
Biological Conservation 77 (1996) 151 15"7 Copyright @ 1996 Elsevier Science Limited Printed in Great Britain. All rights reserved 0006-3207,/96/$15.00+0.0(!
ISLAND RELEASES OF SADDLEBACKS Philesturnus carunculatus IN NEW Z E A L A N D Tim G. Lovegrove* 47 Pupuke Road, Birkenhead, Auckland 10, New Zealand
(Received 12 October 1994; accepted 20 October 1995)
Abstract The success of 45 releases of saddlebacks Philesturnus carunculatus between islands in New Zealand is compared. Forty-three releases were 'immediate' (birds released immediately on arrival at site), and two were 'delayed' (birds released after 12 days' conditioning in an aviary on site). Most releases with a balanced sex ratio on predator-J?ee islands were successful. Others failed because (1) predators were still present, or arrived after release, or (2) too few birds were released. The success of releases may have been enhanced by the birds' limited dispersal, small territories, flocking behaviour, high reproductive rate and broad habitat requirements. Before one release, prior conditioning of the bird~ in an aviary on site did not improve their subsequent survival. Immediate releases shouM be used for wildcaught birds, and the captive period minimised. Conditioning may be appropriate for captive-reared birds" to adjust to the wild. Copyright © 1996 Elsevier Science Ltd
Petroica traversi (Merton, 1990; Reed & Merton, 1991; Butler & Merton, 1992), saddleback releases have outnumbered those of all other small New Zealand forest birds; most of the techniques now used for such birds were tested and refined using saddlebacks (Lovegrove & Veitch, 1994). Like some other New Zealand forest birds (Flack, 1978), saddlebacks are particularly suitable for releases because they have: (1) limited dispersal and are sedentary; (2) flocking behaviour which may facilitate pair formation; (3) small territories, e.g. < 0.4 ha on Cuvier (Lovegrove & O'Callaghan, 1982), which allow large populations on small islands, e.g. 75 birds on < 20 ha (Big I), and 1000 birds on < 150 ha (Cuvier); (4) broad habitat requirements, from shrubland to tall forest; (5) a high reproductive rate. Although saddlebacks have a low reproductive rate in stable long-established populations, they are capable of a high reproductive rate where there is little intraspecific competition (T. G. L., unpublished data). A high reproductive rate allows rapid population expansion and maintenance of genetic variability (Nei et al., 1975). These features are important in many species which colonise islands naturally (Lack, 1976: Fyfe, 1978; Diamond, 1985). Although many immediate releases (Scott & Carpenter, 1987) of saddlebacks after 1960 were successful, high mortality during the first year prevailed on some islands, e.g. Little Barrier and Motukawanui, where respectively only 22 of 50 and eight of 16 birds survived a year after release, and Kapiti where only 13 of 43 were alive 2 months after release in 1987. An experimental delayed release was made in 1988 in the hope that this might result in better survival during pair formation and territory establishment, when losses are usually high (T. G. L., unpublished data). Greater survival of founding birds may improve genetic variability of the survivors (Frankel & Soul& 1981; Shaffer, 1987). Releases have become important for conserving many endangered species, but there is need for further work on the factors affecting success (Fyfe, 1978; Scott & Carpenter, 1987; Griffith et al., 1989; Short et al., 1992: Armstrong & Craig, 1995; Armstrong, 1995). Here I review the outcome of all saddleback releases
Keywords." New Zealand, saddleback, translocation, release methods.
INTRODUCTION Releases of endangered birds in New Zealand have resulted in many populations being established in new or restored island communities (Williams, 1977; Merton, 1975; Atkinson, 1990; Craig, 1990). These have averted the extinction of several taxa, including little spotted kiwi Apteryx owenii, buff weka Gallirallus australis hectori, and South Island saddleback Philesturnus c. carunculatus; the last species was rescued when ship rats Rattus rattus invaded its only remaining habitat (Atkinson & Bell, 1973). The release of North Island saddlebacks P. c. rufusater on Cuvier Island in 1968 may have been the first in which wild birds were re-established where they had been previously extirpated (Merton, 1975; Fyfe, 1978). Conservation of saddlebacks has depended on island releases, because they cannot coexist with carnivores introduced to mainland New Zealand since 1770 (King, 1984). With the possible exception of Chatham Island black robins *Tel.: (64) 9 4806587. 151
152
T. G. Lovegrove
since 1925, and examine the results of immediate and delayed releases on Kapiti Island in 1988. METHODS
Data for this review were derived from Merton (1975), Nillson (1978), Atkinson (1990), Roberts (1991), unpublished reports of the New Zealand Wildlife Service (pre-1987) and of the Department of Conservation (post-1987), and my own knowledge through participating in most North Island saddleback releases since 1977. The immediate and delayed releases on Kapiti in 1988 were similar to others (Lovegrove & Veitch, 1994). On arrival at Kapiti, 20 saddlebacks were released immediately near a 5 × 3 x 2 m aviary, where the remaining 19 birds were held for 12 days before release. (Ideally the two groups should have been released simultaneously, but the costs of multiple trips to remote islands to capture the birds, and other logistical constraints, precluded this.) In captivity a maintenance diet was provided and supplementary food consisting of nectar mix and bird buns (Lovegrove & Veitch, 1994) was available ad lib. near the aviary for all birds after release; this food was replenished daily for 8 weeks, then less frequently until feeding was stopped 12 weeks later. Both releases coincided with an experiment comparing the survival of birds using ratproof (against Rattus norvegicus) roost boxes with those using natural roosts (Lovegrove, 1992). To compensate for the possible differential survival after release, the two groups were split evenly between those released immediately and those with delayed release. RESULTS Review of all releases
Forty-five saddleback releases between 1925 and 1994 included 28 of P. c. rufusater to 11 different islands and 17 of P. c. carunculatus to 13 islands (Table 1). Releases of P. c. rufusater totalled 846 birds, with a mean of 30 per release (SD 13.8, range 6-50); while P. c. carunculatus totalled 464, with a mean of 27 per release (SD 12.l, range 15-59). All but the 1988 and 1989 releases to Kapiti Island were immediate. The two delayed releases were both on Kapiti; they included the release described here, and an experimental release in 1989 testing the effects of familiarity (Armstrong et al., 1994). Some of the source islands have been very productive, and many birds have been removed without adverse effect. The most remarkable was Big Island (20 ha) from which 151 South Island saddlebacks were removed between 1969 and 1978. During this period the mean population at any one time was about 75 birds (Nillson, 1978). In order of importance, the main source islands and numbers removed for North Island saddlebacks have been Cuvier (373), Hen (205) and
Stanley (122); all of these have much larger populations than Big Island (e.g. Cuvier c.1000, Hen c.500 and Stanley c.250). The maximum number of birds removed in any one year was 74 from Cuvier in 1984. Success or failure
I have regarded as successful those releases which produced self-sustaining populations. Eleven of 28 releases of North Island saddlebacks and 10 of 17 releases of South Island saddlebacks were successful. The success rate is higher when analysed on a per island basis because some islands, including unsuccessful ones, had more than one release. The success rate was similar for northern and southern islands on a per island basis, eight of 11 and 10 of 13 respectively. Successful islands had forests ranging in area from 6 ha (Betsy) to over 3000 ha (Little Barrier), and had either Polynesian rats R. exulans or mice Mus musculus as the only rodents (all northern islands), or lacked them entirely (all southern islands). Three successful southern islands (Kundy, Motunui, and Jacky Lee), and one northern one (Mokoia) also had weka Gallirallus australis, a flightless omnivorous rail which sometimes preys on saddleback fledglings (T. G. L., unpublished data). There was a significant relationship between a lack of important predators on islands (i.e. feral cats Felis catus, European rats R. rattus and R. norvegicus, Polynesian rats (from South Island offshore islands only) and stoats Mustela erminea), and the success of translocations (X2~=22-2, p <0.001). Although saddlebacks on islands with wekas did not do as well as those on weka-free islands, surveys indicate that they coexisted: moreover there were sufficient saddlebacks on Kundy Island for birds to be removed in 1980 and 1982. Wekas were removed from Kundy between 1981 and 1985 (Veitch & Bell, 1990), and saddlebacks apparently increased (Roberts, 1991). Two factors appear to be related to the failure of some saddleback releases. (1) The presence of predators, or their arrival after the birds were released. All releases (n=12) of North Island saddlebacks failed on islands with either feral cats (Little Barrier), or a combination of Norway rats R. norvegicus, wekas and feral cats, or Norway rats and wekas (Kapiti) (Turbott, 1947; Wilkinson & Wilkinson, 1952: Lovegrove, 1992). By contrast 10 out of 13 releases of North Island saddlebacks were successful on islands where R. exulans was the only rat (Merton, 1975; T. G. L., unpublished data). All releases (n--5) of South Island saddlebacks onto islands with either R. exulans and wekas (Chetwode), or R. exulans (Putauhinu), have respectively failed or have ailing populations (Nillson, 1978: Roberts, 1991). On Chetwode a combination of R, exulans and wekas may have been detrimental because saddlebacks have coexisted with wekas on Big South Cape, Kundy, Motunui, and Jacky Lee; and with wekas and mice on Mokoia in the absence of rats. On Motukawanui and Maud Islands saddlebacks were
Island releases of saddlebacks in New Zealand
153
Table 1. Summary of saddlebaek translocations to islands 1925-1995 (a) N o r t h Island saddleback Date of release
Source island
Release island
Possible predators
Area No. Result (ha) released
Notes, population size
References
18 Oct 1925 29 Oct 1925 12 Jun 1950 Jan 1964 30 Jan 1966 25 Jan 1968 5 Feb 1968 Mar 1971 23 Jan 1977 20 Jan 1981 6 Feb 1981 12 Feb 1981 19 Feb 1982 3 Mar 1982 10 Mar 1982 Feb 1983 19 Mar 1983 25 Feb 1984 26 Feb 1984 17 Mar 1984 3 Mar I985 10 Oct 1986 6 Mar 1987 18 Apr 1988 26 Sep 1987 24 Aug 1988 26 Aug 1989 12 Apr 1992
Hen Hen Hen Hen Hen Hen Hen Whatupuke Cuvier Hen Cuvier Chickens Hen Cuvier Chickens Hen Cuvier Cuvier Cuvier Hen Cuvier Chickens Cuvier Cuvier Stanley Stanley Stanley Tiritiri
Little Barrier Kapiti Lady Alice Whatupuke Red Mercury Cuvier Fanal Lady Alice Stanley Kapiti Kapiti Kapiti Kapiti Kapiti Kapiti Motukawanui Kapiti Little Barrier Tiritiri Motukawanui Fanal Little Barrier Little Barrier Little Barrier Kapiti Kapiti Kapiti Mokoia
C,K C,N,K,P,W K K K K K K K N,K,P,W N,K,P,W N,K,P,W N,K,P,W N,K,P,W N,K,P,W K N,K,P,W K K K K K K K N,K,W N,K,W N,K,W M,W
3083 1965 155 102 225 170 75 155 100 1965 1965 1965 1965 1965 1965 380 1965 3083 197 380 75 3083 3083 3083 1965 1965 1965 135
Disappeared quickly Survived till March 1931 3 birds, December 1952 c.500 * c.400 * c.1000 * c.5 in 1973 c.300 in 1986 * c.250 1986-89 * Gone by 1985 1 survivor Nov 1991 Gone by 1985 1 survivor Nov 1991 1 survivor 1985 1 survivor 1985 Gone by Aug 1986 # 2 survivors 1985 c.1500 by 1995 * c.200 by 1991 * Gone by Aug 1986 # c.5 survivors 1987 c. 1500 by 1995 * c.1500 by 1995 * c.1500by 1995 * 7 survivors Nov 1991 + 8 survivors Nov 199l + 5 survivors Nov 1991 + c. 140 by Sep 1994
Turbott, 1947 Wilkinson & Wilkinson, 1952 Chambers et al., 1955 Merton, 1965 Merton, 1975 Merton, 1975; Jenkins, 1978 P. F. Jenkins, pers. comm. T. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data Y. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data Y. G. L. unpublished data Craig, 1990 T. G. L. unpublished data C. Hodsell, pets. comm. T. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data Y. G. L. unpublished data T. G. L. unpublished data T. G. L. unpublished data P. Jansen, pers. comm.
Area No. Result (ha) released
Notes, population size
References
9 9 6 23 29 29 25 21 24 25 50 25 22 50 22 16 50 50 24 12 29 42 47 49 43 39 40 36
x x x s s s x s s x x x x x x x x s s x x s s s x x x s
(b) South Island saddleback Date
Source island
Release island
Possible predators
31 Aug 1964 31 Aug 1964 14 Jul 1965 2 Aug t970 Mar 1969 5 Mar 1972
Big South Cape Big South Cape Big South Cape Big Big Big, Kaimohu, and Betsy Big Big Kundy Big, Kaimohu Big, Kaimobu Big, Kaimohu Big, Kaimohu Big, Kundy Big, Kundy North, Jacky Lee
Big Kaimohu Inner Chetwode Inner Chetwode Betsy North and Womens Putauhinu Putauhinu Putauhinu Kundy Maud Maud Motunui Jacky Lee Breaksea Motuara
Nil Nil K,W K,W Nil Nil Nil K K K W Nil Nil W Nil Nil Nil
6 Mar 1974 25 Jan 1976 Feb 1 9 8 4 31 Jan 1978 Jan 1980 Feb 1982 Feb 1981 Feb 1986 Mar 1992 5 Mar 1994
23 11 195 195 6 8 8 141 141 141 19 309 309 48 30 170 59
21 15 30 17 16 19 20 23 22 20 38 34 38 20 46 59 26
s s x x x s s u u u s x x s s s s
c.80 1986 Roberts, 1991 c.30 1978 Nilsson, 1978 Gone by 1973 Merton, 1975 Gone by 1973 Merton, 1975 c.12 May 1978 Nilsson, 1978 c.30 in 1988 Roberts, 1991 c.25 in 1988 Roberts, 1991 c.20 in 1991 Roberts, 1991 c.20 in 199l Roberts. 1991 c.20 in 1991 Roberts, 1991 c.80 1986 Roberts, 1991 Gone by 1983 # Roberts, 1991: Bell, 1983 Gone by 1983 # Roberts, 1991; Bell, 1983 c.60 1991 Roberts, 1991 c.65 1991 Roberts, 1991 30+ survivors March 1993 Rasch & McClelland, 1993 c.30 survivors March 1995 W. Cash. pets. comm.
* Estimate of population based on area of island and habitat quality, transect counts (Cuvier), or time since release (Little Barrier). s Successful translocation (i.e. self-sustaining population). x Failed translocation. u Outcome uncertain (Putauhinu Island, where Polynesian rats have apparently reduced saddleback survival and breeding success). # Stoats invaded Motukawanui Island in about 1985, and Maud Island in 1982. + Survival on Kapiti Island enhanced by addition of roost and nest boxes, but population gradually declining. C, feral cat; K, kiore (Polynesian rat); N, Norway rat; M, mice; P, Australian possum; W, weka. (Note: Australian possums removed from Kapiti Island by 1986, and Polynesian rats removed from Stanley, Red Mercury, Cuvier, Whatupuke and Tiritiri Islands between 1991 and 1994.)
w i p e d o u t a f t e r s t o a t s i n v a d e d (Bell, 1983; T. G . L.,
released. In 1953 p o s s i b l y o n l y t h r e e r e m a i n e d ( C h a m b e r s
u n p u b l i s h e d d a t a ) . N o r t h I s l a n d s a d d l e b a c k s b r e d succ e s s f u l l y o n M o t u k a w a n u i in t h e p r e s e n c e o f R. exulans
et al., 1955). A r e l e a s e o f 21 b i r d s o n t h e s a m e i s l a n d in 1971 s u c c e e d e d .
b e f o r e s t o a t s r e a c h e d t h e i s l a n d (T. G , L. u n p u b l i s h e d
T w o r e l e a s e s o n F a n a l I s l a n d (1968, 1985) f a i l e d f o r
d a t a ) . (2) T o o f e w b i r d s t r a n s l o c a t e d . I n 1950 o n L a d y A l i c e I s l a n d o n l y six b i r d s ( u n k n o w n sex r a t i o ) w e r e
u n k n o w n r e a s o n s . F a n a l (75 h a ) w a s t h e s m a l l e s t i s l a n d where
North
Island
saddlebacks were
released, and
T. G. Lovegrove
154
R. exulans was the only mammal known to be present. Fanal is bigger than many southern islands with successful saddleback populations, and a similar size to Coppermine Island (80 ha), which North Island saddlebacks colonised naturally by flying a 150 m strait from Whatupuke Island (Newman, 1980). Results of immediate and delayed releases in 1988 Although there was no objective measure (by weighing) of the condition of the birds at the time of release all appeared to be healthy, and all fed well in captivity. The birds were not recaptured and weighed before release because the extra handling is stressful. In previous years saddlebacks had an average weight gain of 2.5% after a period in captivity (Lovegrove & Veitch, 1994). After 2 months (by which time most birds had settled and paired), 12 of 20 of the birds released immediately and 15 of 19 of the birds with delayed release were still alive. The difference in survival after two months was not significant (A~1=1-64, p >0-1), and similar numbers of the two groups survived after 1 year. Survivorship of the two groups of birds during the first year is shown in Fig. 1. After release the supplementary food was used by 50% of the birds released immediately and all of the birds in the delayed release. Their survival was not significantly different (X2,=0.93 p >0-1). DISCUSSION Immediate releases of saddlebacks were usually successful so long as the release islands lacked important predators. Successful release islands lacked predators totally (some Stewart Island outliers); or had wekas only (Kundy, Motunui, Jacky Lee); or had mice and wekas (Mokoia); or had R. exulans only (Red Mercury, Cuvier, Whatupuke, Lady Alice, Stanley, Little Barrier, and Tiritiri). 90
---o--- Immediate
7~001 \
~'~,x
•
release
Delayed release
,o
3020100
0
l
i
I
I
1
2
3
4 5 6 7 8 Months since release
l
i
i
i
i
;
i
I
9
1
11
12
Fig. t. Survival of North Island saddlebacks during the first year after immediate (20 birds) and delayed releases (19 birds) in 1988 on Kapiti Island, New Zealand. There was no significant difference in survival after the 2-month territory and pair formation phase, and similar numbers of the two groups survived after 1 year.
All releases on islands lacking important predators where more than 15 birds were released were successful. The release of six birds on Lady Alice in 1950 failed probably because there were too few; a subsequent release of 21 birds succeeded, Surveys showed that half of the birds in some releases failed to survive the first year (T. G. L., unpublished data). If such a decline occurred after the first release on Lady Alice then the tiny population would have been vulnerable. Although that release of six failed, two experimental releases of five South Island robins Petroica australis, and one of seven Chatham Island black robins, succeeded (Flack, 1978; Morris, 1977; Butler & Merton, 1992). Releases of as few as nine saddlebacks might succeed in good habitat, provided the sex ratio is reasonably balanced. A release of nine on Kapiti in 1925 resulted in successful breeding at least until 1931 (Wilkinson and Wilkinson, 1952). The population probably died out as a result of the combined effects of predation by Norway rats, which were found to be important predators of the saddlebacks released on Kapiti between 1981 and 1989 (Lovegrove, 1992); feral cats which were not eradicated from Kapiti until 1934 (Veitch & Bell, 1990); and possibly wekas which may have preyed on some young. Cats have been blamed for the extinction of saddlebacks on Little Barrier last century; and for the demise of birds released in 1925 (Turbott, 1947). These early failures were mainly due to ignorance of the possible effects of predators. Apart from the experimental releases on Kapiti during the 1980s (undertaken because coexistence with R. norvegicus was thought possible), recent releases have all been to islands lacking important predators where the success rate has been high. Since 1964 the aim in saddleback releases has been to move 2 0 4 0 birds, although more were released on some big islands such as Little Barrier, or where experimental programmes were conducted such as on Kapiti. These have been facilitated by improved capture techniques (Merton, 1975), A review of translocations (Griffith et al., 1989) shows that releases of about 40 birds into good habitat will probably be successful, and that releases of more than 80-120 birds do little to increase success. A study of New Zealand translocations (J. g. Craig & C. Reed, pers. comm.) shows no relationship between success and number of birds in releases of five to 366 birds; releases of as few as five birds on predator-free islands are likely to succeed. Inadequate restoration of communities is a continuing problem on Kapiti and Putauhinu Islands. Recent attempts to enhance survival on Kapiti by releasing birds that use roost boxes and providing roost and nest boxes have greatly reduced the level of Norway rat predation; but population modelling suggests that saddlebacks will gradually decline over a 50-70 year period (Lovegrove, 1992). On Putauhinu Island South Island saddlebacks have not thrived as on nearby rodent-free
Island releases o f saddlebacks in New Zealand islands. All birds in the southern populations are derived from previously rodent-free Big South Cape Island. Unlike the North Island subspecies, the South Island birds may be unable to coexist with R. exulans, and in order to survive the population on Putauhinu may need roost and nest boxes, or eradication of R. exulans. The failure of saddlebacks to establish on Inner Chetwode Island has been blamed on wekas, which were numerous and may have preyed on saddlebacks visiting one of the few available water supplies (Merton, 1975). However P. c. carunculatus coexists with weka on several much smaller Stewart Island offliers; and since the population on Putauhinu has struggled to coexist with R. exulans, the presence of this rat on Chetwode (perhaps combined with the effects of wekas) may have been the limiting factor. Saddleback translocations to Maud and Motukawanui Islands should never have been undertaken, because even then stoats were already known to have reached such islands up to 1100 m offshore in New Zealand (Taylor & Tilley, 1984). Any island within 1200 m of the mainland is at risk, although closer islands (e.g. Breaksea) may be secure if they are very exposed (Taylor & Tilley, 1984). Islands for future saddleback releases must be carefully chosen with respect to their risk of stoat invasion. The immediate and delayed releases on Kapiti suggest that little was gained by first conditioning the birds; but this result is based on only one test; more replicates are needed. A single release of stitchbirds Notiomystis cincta using the same methods in 1991 suggested that birds that were released immediately survived better than delayed release birds (Castro et al., 1994a). Griffith et al. 's (1989) review of translocations showed that high-quality habitat at the release site is probably the most important prerequisite. Delayed releases are labour-intensive and costly, and captivity is probably stressful; foods for a maintenance diet may also be unsuitable, time-consuming or difficult to obtain, and there is increased risk of injury or disease (Reed & Stockdale, 1994). Wild-caught birds should be released as soon as possible. Where capture and release points are close together, and where catching is efficient and transport fast, birds may be caught and released within a few hours. This may be the best technique for small insectivores that are difficult to feed. Usually releases are at distant sites, and it may take several days to catch sufficient birds, so a holding aviary is needed near the capture site. The period in captivity should be used to accustom birds to artificial foods that will sustain them during transport, especially if delays are expected (Lovegrove & Veitch, 1994). Supplementary feeding after release may not be necessary for saddlebacks, but stitchbirds on Kapiti depended heavily on supplementary food after release, especially during spring; and one feeder was maintained permanently (Castro et al., 1994b). These differences emphasise the need for trials
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(with related species if possible) to refine techniques before an endangered species is released. The transfers of Chatham Island black robins benefited from the knowledge that as few as five South Island robins could be released successfully (Flack, 1978); and recent transfers of small numbers of yellowheads Mohoua ochrocephala (Dilks et al., 1994) will assist future operations with this species. Delayed releases should be used where birds are captive-bred or where they have had a long stay in captivity. These birds usually need conditioning to adjust" to life in the wild (Temple, 1978a; Berger, 1978; Cade, 1990; Cade & Jones, 1992; Jones et al., 1992). Delayed releases may also be appropriate for migratory species, or those likely to disperse far from the release point (Temple, 1978b), although recent work suggests that the needs of some species may be complex (Akcakaya, 1990; Franzreb, 1990). Delayed releases have also proved successful for captive-reared flocking species such as game birds (Ellis et al., 1978).
ACKNOWLEDGEMENTS Funding for this study was provided by the New Zealand Department of Conservation, the former Department of Lands and Survey, the New Zealand Lottery Grants Board and the University of Auckland Research Committee. I thank the University of Auckland School of Biological Sciences for institutional support, and the Department of Conservation for permission to work on the island reserves. I also wish to thank John Craig, Jared Diamond, Peter Jenkins, Henrik Moller, Ron Moorhouse, Craig Miller, Dick Sibson, Dick Veitch and two anonymous referees for useful comments.
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