- Email: [email protected]
Do meadow birds profit from agri-environment schemes in Dutch agricultural landscapes?
Biological Conservation 142 (2009) 2949–2953
Contents lists available at ScienceDirect
Biological Conservation journal homepage: www.elsevier.com/locate/biocon
Do meadow birds profit from agri-environment schemes in Dutch agricultural landscapes? Angela Breeuwer a, Frank Berendse a,*, Frank Willems b, Ruud Foppen b, Wolf Teunissen b, Hans Schekkerman b, Paul Goedhart c a b c
Nature Conservation and Plant Ecology Group, Wageningen University, Droevendaalsesteeg 3a, 6708 PB Wageningen, The Netherlands SOVON Vogelonderzoek Nederland, Rijksstraatweg 178, 6573 DG Beek-Ubbergen, The Netherlands Biometris, Wageningen University and Research Centre, Bornsesteeg 47, 6708 PD Wageningen, The Netherlands
a r t i c l e
i n f o
Article history: Received 27 February 2009 Received in revised form 13 July 2009 Accepted 25 July 2009 Available online 29 August 2009 Keywords: Agri-environment schemes European policy Haematopus ostralegus Limosa limosa Time series Tringa totanus Vanellus vanellus
a b s t r a c t Since 1992 the European Union helps member states to reverse the loss of biodiversity in agricultural landscapes by the financial support of agri-environment schemes. Long-term studies investigating the effects of these schemes are an essential prerequisite for the development of an effective policy to restore biodiversity on farmland. In Dutch meadow landscapes almost all agri-environment schemes focus on the restoration of meadow bird populations by postponement of the mowing date. Between 1990 and 2002 we measured long-term changes in meadow bird densities in areas with and without agri-environment schemes in the Netherlands, both before and after the start of the contract. During these years bird territories were surveyed during five field visits between 15 March and 15 June. Densities of black-tailed godwit (Limosa limosa), and redshank (Tringa totanus) were higher in the areas with management agreements, but these differences were already present before the start of the contracts. After the start of the management contracts densities of black-tailed godwit and oystercatcher (Haematopus ostralegus) did not increase, while those of lapwing (Vanellus vanellus) and redshank even declined relative to the control areas. It is concluded that the current agri-environment schemes are not sufficient to restore meadow bird populations in Dutch agricultural landscapes. In addition to the prescribed postponement of the mowing date, it is probably necessary to raise groundwater levels and to reduce fertilization to allow for the development of an open vegetation structure that will increase chick survival to sufficiently high levels. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction During the last decades the biodiversity in the agricultural landscapes of Western Europe has declined sharply. Agricultural intensification, greatly accelerated as a result of the EU Common Agricultural Policy (CAP), has led to drastic reductions in the populations of many wild plant and animal species that used to be characteristic of farmland (Chamberlain et al., 2000; Donald et al., 2002; SOVON Vogelonderzoek Nederland, 2003; DEFRA, 2004). A recent overview showed that European farmland birds had declined on average by as much as 34% between 1966 and 2002 (Birdlife International, 2004). In 1992 the EU passed its Agri-Environment Regulation 2078/92 to help member states reverse these developments by means of agri-environment schemes * Corresponding author. Tel.: +31 317 484973; fax: +31 317 419000. E-mail addresses: [email protected] (A. Breeuwer), [email protected] (F. Berendse), [email protected] (F. Willems), [email protected] (R. Foppen), [email protected] (W. Teunissen), [email protected] (H. Schekkerman), [email protected] (P. Goedhart). 0006-3207/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2009.07.020
(European Community, 1997). The regulation recognized the financial burden often associated with more environmentally beneficial management practices. It therefore intended to contribute to the income of the farmers providing environmental services. Costs for agri-environment schemes are partly financed through the EU budget. At present, roughly 25% of the farmland area in the European Union is under some kind of agri-environment program (European Union, 2005). Already in 1975 the Dutch Parliament approved a policy that enabled agreements with farmers who are paid to implement a prescribed management strategy. In 1981 the first management contracts with farmers were implemented, and after 1991 the area managed under such agreements became substantial (>20,000 ha). Thus, the management agreements in the Netherlands have been running now for a relatively long period of time as compared to many other EU member states. The effects of these management agreements may provide insights that can help to increase the effectiveness of the EU policy to restore the biological diversity on farmland in the other member states.
2950
A. Breeuwer et al. / Biological Conservation 142 (2009) 2949–2953
An important part of the Dutch agri-environment schemes focuses on the protection of meadow birds, especially on black-tailed godwit (Limosa limosa L.), lapwing (Vanellus vanellus L.), oystercatcher (Haematopus ostralegus L.) and redshank (Tringa totanus L.). The populations of these species in the Netherlands are strongly dependent on agricultural grasslands. Moreover, the Netherlands harbour 40% and 30% of the total Western populations of blacktailed godwit and oystercatcher, respectively (Teunissen and Soldaat, 2006). The main management adaptation prescribed in the contracts with farmers is the postponement of mowing and other disturbing agricultural activities, such as manure application, to the end of May or June to reduce chick and egg mortality. These measures had a strong ecological justification since postponed mowing has been shown to increase hatching success of nests of lapwings and black-tailed godwits (Beintema and Müskens, 1987), and the availability of invertebrates making up the diet of chicks of black-tailed godwit and other meadow birds (Schekkerman and Beintema, 2007). Postponed mowing also increases the availability of protective cover and has been shown to reduce predation risk for black-tailed godwit chicks (Schekkerman et al., 2009). Schekkerman (2008) showed that the decline of the Dutch population of black-tailed godwits was strongly correlated with a reduced survival of their chicks. An important question is whether meadow birds respond to management agreements by increased local densities, so that a relatively large part of the population can profit from the improved conditions for reproduction. A recent extensive study in the Netherlands that examined the effects of management agreements used a pairwise comparison between control fields and fields with agreements that had been applied for an average period of 5 years (Kleijn et al., 2001, 2004). This study showed that black-tailed godwit and redshank densities were not higher on fields with an agreement, while the agreements even had negative effects on the densities of lapwing and oystercatcher. This study was heavily criticized since it compared densities on just one moment in time, while the development of the local populations in time was not included (Carey, 2001). Here we present the results of the first study that analyzes the changes in the numbers of these species both during a number of years preceding the start of the agreement and during the period thereafter.
2. Methods 2.1. Selection of sites and field surveys Between 1990 and 2002 volunteers and professional ornithologists counted territories of meadow birds in 1040 grassland areas in the Netherlands. A first prerequisite to be able to compare areas with and without management agreements is that those areas provide similar habitats to meadow birds and only differ in management. In the Netherlands farmers could only enter into a management contract if their farms were located within areas designated as sufficiently favorable for meadow birds. As a first step we included only sites within those designated areas. As a second step we selected within each pair sites with and without management agreements, that: (1) had equal areas, (2) were located within 1 km of each other and more than 1 km from other selected sites, (3) had the same soil type and groundwater level and (4) were located in landscapes with a similar structure and at similar distances from roads, buildings and tree lines. From the sites that passed this filter, we only included those pairs where bird counts had been performed in at least two years preceding the start of the agreement and two years after the start
of the agreement (including the year in which the agreement started) and where these counts at the sites with and without contract had been performed in the same year. This strict selection procedure resulted in 28 pairs of sites for oystercatcher and black-tailed godwit. There were no other (subjective) selection criteria than those listed above. For lapwing and redshank the procedure resulted in 26 and 24 pairs of sites, respectively, since these species had not been counted at all sites. Sites were not excluded for the single reason that these species were not present. Sites with management agreements and controls both comprised on average 7.5 ± 5.2 (SD) ha. Twelve pairs of sites were located in the core meadow bird regions of the Netherlands; the others in smaller areas of suitable habitat elsewhere. The development of bird abundance in the study sites on average closely followed the national trend during the study period, except in redshank where it was slightly more positive. Bird territories were surveyed during five field visits between 15 March and 15 June. The location of territories was assessed on the basis of the observations of nests, chicks and adult birds following the guidelines for the Breeding Bird Monitoring project in the Netherlands (van Dijk, 1996) which resembles the method used by the Common Bird Census in the UK.
2.2. Statistical analysis In the first analysis we compared territory densities of the four bird species before and after the start of the agreement in the areas with and without contract, using a Generalized Linear Model with a log link (Genstat 5 Committee, 1993) that included the factors pair, year and management agreement (Genstat 5 Committee, 1993). Year was included as factor since densities may fluctuate from year to year due to variations in climatic conditions. To identify the distribution of the number of territories per site, we explored the variance to mean relationship for each species. On the basis of this analysis we assumed that the numbers of breeding pairs followed a Poisson distribution (McCullagh and Nelder, 1989). If necessary, overdispersion was accounted for by inflating the variance of the Poisson distribution with a constant factor. The area of the sites (that was equal within each pair) was included as an offset variable to convert territory counts to densities. In a second analysis we compared the change in densities over time in control and managed areas before and after the start of the contracts, thus looking at effects on population development rather than density. For this purpose, we added to the first model the number of years preceding or after the start of the management agreement as covariate, separately for the sites with and without management agreement. The slopes of the change in density over time were calculated relative to those for the control sites in the period before the start of the contract. In a third analysis we included the interaction between the effects of management agreement and within-pair distance between control and management sites, to control for the possible overflow of birds to neighboring areas. If agri-environment schemes lead to an increased reproduction and young birds settle not only at the managed site, but also in neighboring areas, we would expect that the difference between control and managed sites would decrease with decreasing within-pair distance. The effects of factors and differences between regression slopes were tested using the likelihood ratio test (Genstat 5 Committee, 1993). The model used to calculate the graphical presentation of the regression lines (Fig. 1) included only the covariates pair, and management agreement and the number of years before and after the start of the agreement as covariates.
A. Breeuwer et al. / Biological Conservation 142 (2009) 2949–2953
2951
Fig. 1. The regression lines through the densities of the four meadow bird species in areas with management agreements (green, full line) and control areas (red, broken line) versus the number of years preceding or after the start of the agreement. The presented lines are calculated using a Generalized Linear Model (with a log link) including the factors pair and management agreement. They are calculated separately for the periods before and after the start of the agreement. Different small letters denote significant differences (p < 0.05) between the average density in areas with and without management agreement. Different capitals denote significant differences (p < 0.05) between the slopes in areas with and without management agreement before and after the start of the contracts. Note that in panel (a) there were no significant differences between average densities neither between slopes; in panel (c) there were no significant differences between average densities after the start of the contracts.
3. Results 3.1. Territory densities Densities of the oystercatcher did not differ between areas with and without management agreement, neither before nor after the start of the agreements (Fig. 1a). In the period before the start of the agreements the average densities of black-tailed godwit, lapwing and redshank were higher on the managed fields than on the control site (p < 0.001; Fig. 1b–d). In the period after the start of the contract the average densities of black-tailed godwits and redshanks were still higher in the managed areas (p < 0.001). But the difference between densities of lapwings in the managed and control areas was no longer significant (p = 0.124).
3.2. Changes in density The slopes of the change in oystercatcher densities over time were indistinguishable between contracted sites and controls both before and after the start of the management agreements (Fig. 1a). Likewise, changes in black-tailed godwit densities did not differ significantly between the treatments either before or after the start of the management agreements (Fig. 1b). After the start of the contracts changes in black-tailed godwit numbers on the managed fields were more negative than in the period preceding it (difference between slopes before and after start of the contract: p = 0.03), while the changes on control sites before and after the start of agreements did not differ.
Before the management agreements became effective, regression slopes of lapwing numbers did not differ between fields with and without agreement (Fig. 1c). After the start of the agreement the numbers on the managed fields decreased significantly faster than the numbers on the control fields (p = 0.002). Redshank numbers followed a similar pattern (Fig. 1d). Before the start of the agreement changes in numbers did not differ significantly, but thereafter the numbers on the fields with conventional management increased relative to the sites with management contracts (p = 0.029). 3.3. Effects of distance between paired contract and control sites We tested the interaction between the effects of management agreement and within-pair distance between control and management sites to investigate the effects of a possible overflow of birds to neighboring areas. This interaction was not significant for average densities of oystercatcher (p = 0.685), but highly significant for densities of black-tailed godwit, lapwing and redshank (p < 0.001). For these three species the difference between densities in areas with and without agreement increased with increasing distance between the contract and control site. Hence, models including the distance between managed and control fields led to the same conclusions as the models without this second covariate. There were no significant differences between the changes in oystercatcher and black-tailed godwit densities in areas with and without contract (Fig. 2a and b), while there were significant negative effects on the dynamics of lapwing and redshank numbers at sites with agri-environment schemes (Fig. 2c and d).
2952
A. Breeuwer et al. / Biological Conservation 142 (2009) 2949–2953
slope (yr-1)
0.20
(b) black-tailed godwit
(a) oystercatcher
0.20
0.10
0.10
0.00
0.00
-0.10
-0.10
ab
b
b
-0.20
-0.20 before
0.20
a
before
after
(c) lapwing 0.20
after
(d) redshank
slope (yr-1)
b
0.10
ab
0.10 b
0.00
ab
ab
0.00
-0.10
a
ab
a
-0.10 -0.20
-0.20 before
after
before
after
Fig. 2. The regression coefficients calculated using the Generalized Linear Model including the factors year, pair, management agreement and the covariates years since start of agreement and distance between paired sites. The coefficients were estimated for the trends in time in areas with management agreements (right, crossed, green) and control areas (left, hatched, red) during the years before and after the start of the agreement. The coefficients are estimated relative to the trends in the control areas during the period before the start of the agreement. Different letters denote significant differences between coefficients (p < 0.05).
4. Discussion In many cases contracts with farmers have been implemented on fields with higher than average densities of black-tailed godwit, lapwing and redshank. Apparently, there is a strong preference among farmers and governmental representatives to start contracts on fields with high densities of these species. This selection increases the part of the bird population that can benefit from these measures, but it is also an important pitfall when we try to estimate the effectiveness of agri-environment schemes by comparing densities at sites with and without contracts. In our study we were able to avoid this pitfall by comparing changes in densities in areas with and without contracts both before and after their implementation. The agreements did not have positive effects on the number of black-tailed godwits, and even had significant negative effects on the number of lapwings and redshanks relative to their numbers on control fields. Although these results are in line with the outcome of earlier studies (Kleijn et al., 2001, 2004; Kleijn and Sutherland, 2003; Berendse et al., 2004), it is still surprising that we did not find the expected positive effects. Studies in the UK that compared densities of – amongst others – cirl bunting (Emberiza cirlus) in sites with and without agri-environment schemes did find positive effects (Carey, 2001). But also here, at least in some cases densities on managed sites were already significantly higher before the start of the schemes (Peach et al., 2001). Several Dutch studies show that postponing agricultural activities to June reduces egg and chick mortality (Beintema and Müskens, 1987; Schekkerman and Beintema, 2007; Schekkerman et al., 2009). A large part of the studies on the effects of agri-environment schemes on reproduction have focused on the black-tailed godwit. In this species chick survival was positively correlated with the proportion of the grassland area not yet mown in late May or early June or with the average mowing date (Schekkerman and Müskens, 2000; Schekkerman et al., 2008).
Nevertheless, the large scale application of agri-environment schemes that included postponement of mowing did not result in an overall increase in the number of breeding birds (Teunissen and Soldaat, 2006). Similar results are found on arable fields in the UK where skylarks were found to have a relatively high hatching success in fields with winter wheat, while local densities in this crop type were not increased (Donald et al., 2001). An important and still unanswered question is whether in the rapidly changing agricultural landscape the environmental cues that birds use for the selection of breeding habitats are still those that are most appropriate. There are two major alternative explanations for the lack of positive effects that we observed. The first possible hypothesis is that the improved conditions for reproduction do not result in increased local densities, but in an increased overflow of birds to neighboring areas. An important gap in our present knowledge is that we do not know where the young birds recruit into the breeding population. Including the distance between managed and control fields in the statistical model did, however, not change the main results of our analysis (i.e. no or even negative effects of management agreements). In addition, the significant decline of the lapwing numbers on the managed fields relative to the control fields contradicts this hypothesis. The second possible explanation is that the prescribed and paid management measures are not sufficient. On the basis of adult mortality rates of black-tailed godwits, it was calculated that the minimum reproductive output to balance losses from mortality was 0.6–0.7 fledged young/pair (Schekkerman and Müskens, 2000). Detailed studies on chick survival revealed that this level of productivity is often not met even in sites with management agreements (Schekkerman and Müskens, 2000; Schekkerman et al., 2008). Many environmental factors in the agricultural landscape have changed during the last decades. Among the changes that had major impacts on the life cycles of farmland birds, are earlier, more rapid and frequent mowing, increased cattle densities, increased fertilization and reseeding of grassland, increased
A. Breeuwer et al. / Biological Conservation 142 (2009) 2949–2953
application of pesticides and antihelmintica, lowered water tables and increased predator densities. Management agreements generally include only those prescriptions that can easily be incorporated in modern farming practice, such as postponed mowing. Others, such as increased groundwater levels, are generally considered unacceptable by farmers, and are in most cases not included in the Dutch schemes. Chick mortality has been found to be reduced when mowing is postponed as prescribed by the management agreements (Schekkerman, 2008). But when former water tables are not restored and fall in late spring, the adult birds may experience problems due to lack of available prey items and stop producing replacement clutches, or anticipate such problems and settle elsewhere. Even more important is that in most cases fertilization levels are not sufficiently reduced when mowing is postponed which often results in very dense swards, a problem that is aggravated by an earlier onset of vegetation growth due to climate change. The dense structure of these swards does not allow chicks of black-tailed godwits to move around and to collect sufficient numbers of prey items which generally are small insect in the upper part of the vegetation (Schekkerman, 2008). In addition to the prescribed postponement of the mowing date it is probably necessary to raise groundwater levels and to reduce fertilization to allow for the development of an open vegetation structure that might increase chick survival to sufficiently high levels. 5. Conclusions Agri-environment schemes with management prescriptions that are appropriate by themselves might be insufficient for the recovery of the target species, if they do not relax all limiting factors. The effects of packages of management prescriptions on the dynamics of bird populations on farmland are complicated and difficult to predict. Continuous evaluation of agri-environment schemes (including the period before the start of the agreement and in control areas without agreement) is an essential prerequisite to develop a new and effective policy, so that our farmland birds can really recover from the EU’s former agricultural policy. Acknowledgements The Dienst Landelijk Gebied kindly provided the data about the management agreements. Birdlife The Netherlands and the Office for Environmental Outlooks provided financial support. We thank all volunteer and professional ornithologists that collected the field data. References Beintema, J., Müskens, G.J.D.M., 1987. Nesting success of birds breeding in Dutch agricultural grasslands. Journal of Applied Ecology 24, 743–758.
2953
Berendse, F., Chamberlain, D., Kleijn, D., Schekkerman, H., 2004. Declining biodiversity in agricultural landscapes and the effectiveness of agrienvironment schemes. Ambio 33, 499–502. Birdlife International, 2004. State of the World’s Birds 2004: an Indication for our Changing World. Birdlife International, Cambridge, United Kingdom. Carey, P.D., 2001. Schemes are monitored and effective in the UK. Nature 414, 687. Chamberlain, D.E., Fuller, R.J., Bunce, R.G.H., Duckworth, J.C., Shrubb, M., 2000. Changes in the abundance of farmland birds in relation to the timing of agricultural intensification in England and Wales. Journal of Applied Ecology 37, 771–788. DEFRA (Department for Environment Food and Rural Affairs), 2004. Sustainable Development Indicators in Your Pocket 2004. Defra Publications, London, United Kingdom. Donald, P.F., Green, R.E., Heath, M.F., 2001. Agricultural intensification and the collapse of Europe’s farmland bird populations. Proceedings of the Royal Society of London, Series B Biological Sciences 268, 25–29. Donald, P.F., Evans, A.D., Muirhead, L.B., Buckingham, D.L., Kirby, W.B., Schmitt, S.I.A., 2002. Survival rates, causes of failure and productivity of Skylark Alauda arvensis nests on lowland farmland. Ibis 144, 652–664. European Community, 1997. Agenda 2000, Vol. 1: For a Stronger and Wider EU. Office for Official Publications of the European Communities, Luxembourg. European Union, 2005. Agri-Environment Measures – Overview on General Principles, Types of Measures, and Application, European Commission. Directorate General for Agriculture and Rural Development.. Genstat 5 Committee, 1993. Genstat 5 Release 3 Reference Manual. Oxford University Press, Oxford, United Kingdom. Kleijn, D., Sutherland, W.J., 2003. How effective are agri-environment schemes in maintaining and conserving biodiversity? Journal of Applied Ecology 40, 947– 969. Kleijn, D., Berendse, F., Smit, R., Gilissen, N., 2001. Agri-environment schemes do not effectively protect biodiversity in Dutch agricultural landscapes. Nature 413, 723–725. Kleijn, D., Berendse, F., Smit, R., Gilissen, N., Smit, J., Brak, B., Groeneveld, R., 2004. Ecological effectiveness of agri-environment schemes in different agricultural landscapes in the Netherlands. Conservation Biology 18, 776–786. McCullagh, P., Nelder, J.A., 1989. Generalized Linear Models, second ed. Chapman and Hall, London, United Kingdom. Peach, W.J., Lovett, L.J., Wotton, S.R., Jeffs, C., 2001. Countryside stewardship delivers cirl buntings (Emberiza cirlus) in Devon, UK. Biological Conservation 101, 361–373. Schekkerman, H., 2008. Precocial problems: Shorebird chick performance in relation to weather, farming, and predation. Alterra Scientific contributions 24, 1–228. Schekkerman, H., Beintema, A.J., 2007. Abundance of invertebrates and foraging success of Black-tailed Godwit Limosa limosa chicks in relation to agricultural grassland management. Ardea 95, 39–54. Schekkerman, H., Müskens, G., 2000. Do black-tailed godwits (Limosa limosa) produce sufficient numbers of offspring to maintain a sustainable population? Limosa 73, 121–134 (in Dutch). Schekkerman, H., Teunissen, W., Oosterveld, E., 2008. The effect of ‘mosaic management’ on the demography of black-tailed godwit Limosa limosa on farmland. Journal of Applied Ecology 45, 1067–1075. Schekkerman, H., Teunissen, W., Oosterveld, E., 2009. Mortality of shorebird chicks in lowland wet grasslands: interactions between predation and agricultural practice. Journal of Ornithology 150, 133–145. SOVON Vogelonderzoek Nederland, 2003. Atlas van de Nederlandse Broedvogels 1998–2000. Nationaal Natuurhistorisch Museum Naturalis, KNNV Uitgeverij, European Invertebrate Survey Nederland, Leiden, The Netherlands (in Dutch). Teunissen, W.A., Soldaat, L.L., 2006. Recente aantalsontwikkeling van weidevogels in Nederland. De Levende Natuur 107, 70–74. van Dijk, A.J., 1996. Surveying Breeding Birds in Sample Plots, Manual of the Breeding Bird Monitoring Project. SOVON, Beek-Ubbergen, The Netherlands (in Dutch).
Contents lists available at ScienceDirect
Biological Conservation journal homepage: www.elsevier.com/locate/biocon
Do meadow birds profit from agri-environment schemes in Dutch agricultural landscapes? Angela Breeuwer a, Frank Berendse a,*, Frank Willems b, Ruud Foppen b, Wolf Teunissen b, Hans Schekkerman b, Paul Goedhart c a b c
Nature Conservation and Plant Ecology Group, Wageningen University, Droevendaalsesteeg 3a, 6708 PB Wageningen, The Netherlands SOVON Vogelonderzoek Nederland, Rijksstraatweg 178, 6573 DG Beek-Ubbergen, The Netherlands Biometris, Wageningen University and Research Centre, Bornsesteeg 47, 6708 PD Wageningen, The Netherlands
a r t i c l e
i n f o
Article history: Received 27 February 2009 Received in revised form 13 July 2009 Accepted 25 July 2009 Available online 29 August 2009 Keywords: Agri-environment schemes European policy Haematopus ostralegus Limosa limosa Time series Tringa totanus Vanellus vanellus
a b s t r a c t Since 1992 the European Union helps member states to reverse the loss of biodiversity in agricultural landscapes by the financial support of agri-environment schemes. Long-term studies investigating the effects of these schemes are an essential prerequisite for the development of an effective policy to restore biodiversity on farmland. In Dutch meadow landscapes almost all agri-environment schemes focus on the restoration of meadow bird populations by postponement of the mowing date. Between 1990 and 2002 we measured long-term changes in meadow bird densities in areas with and without agri-environment schemes in the Netherlands, both before and after the start of the contract. During these years bird territories were surveyed during five field visits between 15 March and 15 June. Densities of black-tailed godwit (Limosa limosa), and redshank (Tringa totanus) were higher in the areas with management agreements, but these differences were already present before the start of the contracts. After the start of the management contracts densities of black-tailed godwit and oystercatcher (Haematopus ostralegus) did not increase, while those of lapwing (Vanellus vanellus) and redshank even declined relative to the control areas. It is concluded that the current agri-environment schemes are not sufficient to restore meadow bird populations in Dutch agricultural landscapes. In addition to the prescribed postponement of the mowing date, it is probably necessary to raise groundwater levels and to reduce fertilization to allow for the development of an open vegetation structure that will increase chick survival to sufficiently high levels. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction During the last decades the biodiversity in the agricultural landscapes of Western Europe has declined sharply. Agricultural intensification, greatly accelerated as a result of the EU Common Agricultural Policy (CAP), has led to drastic reductions in the populations of many wild plant and animal species that used to be characteristic of farmland (Chamberlain et al., 2000; Donald et al., 2002; SOVON Vogelonderzoek Nederland, 2003; DEFRA, 2004). A recent overview showed that European farmland birds had declined on average by as much as 34% between 1966 and 2002 (Birdlife International, 2004). In 1992 the EU passed its Agri-Environment Regulation 2078/92 to help member states reverse these developments by means of agri-environment schemes * Corresponding author. Tel.: +31 317 484973; fax: +31 317 419000. E-mail addresses: [email protected] (A. Breeuwer), [email protected] (F. Berendse), [email protected] (F. Willems), [email protected] (R. Foppen), [email protected] (W. Teunissen), [email protected] (H. Schekkerman), [email protected] (P. Goedhart). 0006-3207/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2009.07.020
(European Community, 1997). The regulation recognized the financial burden often associated with more environmentally beneficial management practices. It therefore intended to contribute to the income of the farmers providing environmental services. Costs for agri-environment schemes are partly financed through the EU budget. At present, roughly 25% of the farmland area in the European Union is under some kind of agri-environment program (European Union, 2005). Already in 1975 the Dutch Parliament approved a policy that enabled agreements with farmers who are paid to implement a prescribed management strategy. In 1981 the first management contracts with farmers were implemented, and after 1991 the area managed under such agreements became substantial (>20,000 ha). Thus, the management agreements in the Netherlands have been running now for a relatively long period of time as compared to many other EU member states. The effects of these management agreements may provide insights that can help to increase the effectiveness of the EU policy to restore the biological diversity on farmland in the other member states.
2950
A. Breeuwer et al. / Biological Conservation 142 (2009) 2949–2953
An important part of the Dutch agri-environment schemes focuses on the protection of meadow birds, especially on black-tailed godwit (Limosa limosa L.), lapwing (Vanellus vanellus L.), oystercatcher (Haematopus ostralegus L.) and redshank (Tringa totanus L.). The populations of these species in the Netherlands are strongly dependent on agricultural grasslands. Moreover, the Netherlands harbour 40% and 30% of the total Western populations of blacktailed godwit and oystercatcher, respectively (Teunissen and Soldaat, 2006). The main management adaptation prescribed in the contracts with farmers is the postponement of mowing and other disturbing agricultural activities, such as manure application, to the end of May or June to reduce chick and egg mortality. These measures had a strong ecological justification since postponed mowing has been shown to increase hatching success of nests of lapwings and black-tailed godwits (Beintema and Müskens, 1987), and the availability of invertebrates making up the diet of chicks of black-tailed godwit and other meadow birds (Schekkerman and Beintema, 2007). Postponed mowing also increases the availability of protective cover and has been shown to reduce predation risk for black-tailed godwit chicks (Schekkerman et al., 2009). Schekkerman (2008) showed that the decline of the Dutch population of black-tailed godwits was strongly correlated with a reduced survival of their chicks. An important question is whether meadow birds respond to management agreements by increased local densities, so that a relatively large part of the population can profit from the improved conditions for reproduction. A recent extensive study in the Netherlands that examined the effects of management agreements used a pairwise comparison between control fields and fields with agreements that had been applied for an average period of 5 years (Kleijn et al., 2001, 2004). This study showed that black-tailed godwit and redshank densities were not higher on fields with an agreement, while the agreements even had negative effects on the densities of lapwing and oystercatcher. This study was heavily criticized since it compared densities on just one moment in time, while the development of the local populations in time was not included (Carey, 2001). Here we present the results of the first study that analyzes the changes in the numbers of these species both during a number of years preceding the start of the agreement and during the period thereafter.
2. Methods 2.1. Selection of sites and field surveys Between 1990 and 2002 volunteers and professional ornithologists counted territories of meadow birds in 1040 grassland areas in the Netherlands. A first prerequisite to be able to compare areas with and without management agreements is that those areas provide similar habitats to meadow birds and only differ in management. In the Netherlands farmers could only enter into a management contract if their farms were located within areas designated as sufficiently favorable for meadow birds. As a first step we included only sites within those designated areas. As a second step we selected within each pair sites with and without management agreements, that: (1) had equal areas, (2) were located within 1 km of each other and more than 1 km from other selected sites, (3) had the same soil type and groundwater level and (4) were located in landscapes with a similar structure and at similar distances from roads, buildings and tree lines. From the sites that passed this filter, we only included those pairs where bird counts had been performed in at least two years preceding the start of the agreement and two years after the start
of the agreement (including the year in which the agreement started) and where these counts at the sites with and without contract had been performed in the same year. This strict selection procedure resulted in 28 pairs of sites for oystercatcher and black-tailed godwit. There were no other (subjective) selection criteria than those listed above. For lapwing and redshank the procedure resulted in 26 and 24 pairs of sites, respectively, since these species had not been counted at all sites. Sites were not excluded for the single reason that these species were not present. Sites with management agreements and controls both comprised on average 7.5 ± 5.2 (SD) ha. Twelve pairs of sites were located in the core meadow bird regions of the Netherlands; the others in smaller areas of suitable habitat elsewhere. The development of bird abundance in the study sites on average closely followed the national trend during the study period, except in redshank where it was slightly more positive. Bird territories were surveyed during five field visits between 15 March and 15 June. The location of territories was assessed on the basis of the observations of nests, chicks and adult birds following the guidelines for the Breeding Bird Monitoring project in the Netherlands (van Dijk, 1996) which resembles the method used by the Common Bird Census in the UK.
2.2. Statistical analysis In the first analysis we compared territory densities of the four bird species before and after the start of the agreement in the areas with and without contract, using a Generalized Linear Model with a log link (Genstat 5 Committee, 1993) that included the factors pair, year and management agreement (Genstat 5 Committee, 1993). Year was included as factor since densities may fluctuate from year to year due to variations in climatic conditions. To identify the distribution of the number of territories per site, we explored the variance to mean relationship for each species. On the basis of this analysis we assumed that the numbers of breeding pairs followed a Poisson distribution (McCullagh and Nelder, 1989). If necessary, overdispersion was accounted for by inflating the variance of the Poisson distribution with a constant factor. The area of the sites (that was equal within each pair) was included as an offset variable to convert territory counts to densities. In a second analysis we compared the change in densities over time in control and managed areas before and after the start of the contracts, thus looking at effects on population development rather than density. For this purpose, we added to the first model the number of years preceding or after the start of the management agreement as covariate, separately for the sites with and without management agreement. The slopes of the change in density over time were calculated relative to those for the control sites in the period before the start of the contract. In a third analysis we included the interaction between the effects of management agreement and within-pair distance between control and management sites, to control for the possible overflow of birds to neighboring areas. If agri-environment schemes lead to an increased reproduction and young birds settle not only at the managed site, but also in neighboring areas, we would expect that the difference between control and managed sites would decrease with decreasing within-pair distance. The effects of factors and differences between regression slopes were tested using the likelihood ratio test (Genstat 5 Committee, 1993). The model used to calculate the graphical presentation of the regression lines (Fig. 1) included only the covariates pair, and management agreement and the number of years before and after the start of the agreement as covariates.
A. Breeuwer et al. / Biological Conservation 142 (2009) 2949–2953
2951
Fig. 1. The regression lines through the densities of the four meadow bird species in areas with management agreements (green, full line) and control areas (red, broken line) versus the number of years preceding or after the start of the agreement. The presented lines are calculated using a Generalized Linear Model (with a log link) including the factors pair and management agreement. They are calculated separately for the periods before and after the start of the agreement. Different small letters denote significant differences (p < 0.05) between the average density in areas with and without management agreement. Different capitals denote significant differences (p < 0.05) between the slopes in areas with and without management agreement before and after the start of the contracts. Note that in panel (a) there were no significant differences between average densities neither between slopes; in panel (c) there were no significant differences between average densities after the start of the contracts.
3. Results 3.1. Territory densities Densities of the oystercatcher did not differ between areas with and without management agreement, neither before nor after the start of the agreements (Fig. 1a). In the period before the start of the agreements the average densities of black-tailed godwit, lapwing and redshank were higher on the managed fields than on the control site (p < 0.001; Fig. 1b–d). In the period after the start of the contract the average densities of black-tailed godwits and redshanks were still higher in the managed areas (p < 0.001). But the difference between densities of lapwings in the managed and control areas was no longer significant (p = 0.124).
3.2. Changes in density The slopes of the change in oystercatcher densities over time were indistinguishable between contracted sites and controls both before and after the start of the management agreements (Fig. 1a). Likewise, changes in black-tailed godwit densities did not differ significantly between the treatments either before or after the start of the management agreements (Fig. 1b). After the start of the contracts changes in black-tailed godwit numbers on the managed fields were more negative than in the period preceding it (difference between slopes before and after start of the contract: p = 0.03), while the changes on control sites before and after the start of agreements did not differ.
Before the management agreements became effective, regression slopes of lapwing numbers did not differ between fields with and without agreement (Fig. 1c). After the start of the agreement the numbers on the managed fields decreased significantly faster than the numbers on the control fields (p = 0.002). Redshank numbers followed a similar pattern (Fig. 1d). Before the start of the agreement changes in numbers did not differ significantly, but thereafter the numbers on the fields with conventional management increased relative to the sites with management contracts (p = 0.029). 3.3. Effects of distance between paired contract and control sites We tested the interaction between the effects of management agreement and within-pair distance between control and management sites to investigate the effects of a possible overflow of birds to neighboring areas. This interaction was not significant for average densities of oystercatcher (p = 0.685), but highly significant for densities of black-tailed godwit, lapwing and redshank (p < 0.001). For these three species the difference between densities in areas with and without agreement increased with increasing distance between the contract and control site. Hence, models including the distance between managed and control fields led to the same conclusions as the models without this second covariate. There were no significant differences between the changes in oystercatcher and black-tailed godwit densities in areas with and without contract (Fig. 2a and b), while there were significant negative effects on the dynamics of lapwing and redshank numbers at sites with agri-environment schemes (Fig. 2c and d).
2952
A. Breeuwer et al. / Biological Conservation 142 (2009) 2949–2953
slope (yr-1)
0.20
(b) black-tailed godwit
(a) oystercatcher
0.20
0.10
0.10
0.00
0.00
-0.10
-0.10
ab
b
b
-0.20
-0.20 before
0.20
a
before
after
(c) lapwing 0.20
after
(d) redshank
slope (yr-1)
b
0.10
ab
0.10 b
0.00
ab
ab
0.00
-0.10
a
ab
a
-0.10 -0.20
-0.20 before
after
before
after
Fig. 2. The regression coefficients calculated using the Generalized Linear Model including the factors year, pair, management agreement and the covariates years since start of agreement and distance between paired sites. The coefficients were estimated for the trends in time in areas with management agreements (right, crossed, green) and control areas (left, hatched, red) during the years before and after the start of the agreement. The coefficients are estimated relative to the trends in the control areas during the period before the start of the agreement. Different letters denote significant differences between coefficients (p < 0.05).
4. Discussion In many cases contracts with farmers have been implemented on fields with higher than average densities of black-tailed godwit, lapwing and redshank. Apparently, there is a strong preference among farmers and governmental representatives to start contracts on fields with high densities of these species. This selection increases the part of the bird population that can benefit from these measures, but it is also an important pitfall when we try to estimate the effectiveness of agri-environment schemes by comparing densities at sites with and without contracts. In our study we were able to avoid this pitfall by comparing changes in densities in areas with and without contracts both before and after their implementation. The agreements did not have positive effects on the number of black-tailed godwits, and even had significant negative effects on the number of lapwings and redshanks relative to their numbers on control fields. Although these results are in line with the outcome of earlier studies (Kleijn et al., 2001, 2004; Kleijn and Sutherland, 2003; Berendse et al., 2004), it is still surprising that we did not find the expected positive effects. Studies in the UK that compared densities of – amongst others – cirl bunting (Emberiza cirlus) in sites with and without agri-environment schemes did find positive effects (Carey, 2001). But also here, at least in some cases densities on managed sites were already significantly higher before the start of the schemes (Peach et al., 2001). Several Dutch studies show that postponing agricultural activities to June reduces egg and chick mortality (Beintema and Müskens, 1987; Schekkerman and Beintema, 2007; Schekkerman et al., 2009). A large part of the studies on the effects of agri-environment schemes on reproduction have focused on the black-tailed godwit. In this species chick survival was positively correlated with the proportion of the grassland area not yet mown in late May or early June or with the average mowing date (Schekkerman and Müskens, 2000; Schekkerman et al., 2008).
Nevertheless, the large scale application of agri-environment schemes that included postponement of mowing did not result in an overall increase in the number of breeding birds (Teunissen and Soldaat, 2006). Similar results are found on arable fields in the UK where skylarks were found to have a relatively high hatching success in fields with winter wheat, while local densities in this crop type were not increased (Donald et al., 2001). An important and still unanswered question is whether in the rapidly changing agricultural landscape the environmental cues that birds use for the selection of breeding habitats are still those that are most appropriate. There are two major alternative explanations for the lack of positive effects that we observed. The first possible hypothesis is that the improved conditions for reproduction do not result in increased local densities, but in an increased overflow of birds to neighboring areas. An important gap in our present knowledge is that we do not know where the young birds recruit into the breeding population. Including the distance between managed and control fields in the statistical model did, however, not change the main results of our analysis (i.e. no or even negative effects of management agreements). In addition, the significant decline of the lapwing numbers on the managed fields relative to the control fields contradicts this hypothesis. The second possible explanation is that the prescribed and paid management measures are not sufficient. On the basis of adult mortality rates of black-tailed godwits, it was calculated that the minimum reproductive output to balance losses from mortality was 0.6–0.7 fledged young/pair (Schekkerman and Müskens, 2000). Detailed studies on chick survival revealed that this level of productivity is often not met even in sites with management agreements (Schekkerman and Müskens, 2000; Schekkerman et al., 2008). Many environmental factors in the agricultural landscape have changed during the last decades. Among the changes that had major impacts on the life cycles of farmland birds, are earlier, more rapid and frequent mowing, increased cattle densities, increased fertilization and reseeding of grassland, increased
A. Breeuwer et al. / Biological Conservation 142 (2009) 2949–2953
application of pesticides and antihelmintica, lowered water tables and increased predator densities. Management agreements generally include only those prescriptions that can easily be incorporated in modern farming practice, such as postponed mowing. Others, such as increased groundwater levels, are generally considered unacceptable by farmers, and are in most cases not included in the Dutch schemes. Chick mortality has been found to be reduced when mowing is postponed as prescribed by the management agreements (Schekkerman, 2008). But when former water tables are not restored and fall in late spring, the adult birds may experience problems due to lack of available prey items and stop producing replacement clutches, or anticipate such problems and settle elsewhere. Even more important is that in most cases fertilization levels are not sufficiently reduced when mowing is postponed which often results in very dense swards, a problem that is aggravated by an earlier onset of vegetation growth due to climate change. The dense structure of these swards does not allow chicks of black-tailed godwits to move around and to collect sufficient numbers of prey items which generally are small insect in the upper part of the vegetation (Schekkerman, 2008). In addition to the prescribed postponement of the mowing date it is probably necessary to raise groundwater levels and to reduce fertilization to allow for the development of an open vegetation structure that might increase chick survival to sufficiently high levels. 5. Conclusions Agri-environment schemes with management prescriptions that are appropriate by themselves might be insufficient for the recovery of the target species, if they do not relax all limiting factors. The effects of packages of management prescriptions on the dynamics of bird populations on farmland are complicated and difficult to predict. Continuous evaluation of agri-environment schemes (including the period before the start of the agreement and in control areas without agreement) is an essential prerequisite to develop a new and effective policy, so that our farmland birds can really recover from the EU’s former agricultural policy. Acknowledgements The Dienst Landelijk Gebied kindly provided the data about the management agreements. Birdlife The Netherlands and the Office for Environmental Outlooks provided financial support. We thank all volunteer and professional ornithologists that collected the field data. References Beintema, J., Müskens, G.J.D.M., 1987. Nesting success of birds breeding in Dutch agricultural grasslands. Journal of Applied Ecology 24, 743–758.
2953
Berendse, F., Chamberlain, D., Kleijn, D., Schekkerman, H., 2004. Declining biodiversity in agricultural landscapes and the effectiveness of agrienvironment schemes. Ambio 33, 499–502. Birdlife International, 2004. State of the World’s Birds 2004: an Indication for our Changing World. Birdlife International, Cambridge, United Kingdom. Carey, P.D., 2001. Schemes are monitored and effective in the UK. Nature 414, 687. Chamberlain, D.E., Fuller, R.J., Bunce, R.G.H., Duckworth, J.C., Shrubb, M., 2000. Changes in the abundance of farmland birds in relation to the timing of agricultural intensification in England and Wales. Journal of Applied Ecology 37, 771–788. DEFRA (Department for Environment Food and Rural Affairs), 2004. Sustainable Development Indicators in Your Pocket 2004. Defra Publications, London, United Kingdom. Donald, P.F., Green, R.E., Heath, M.F., 2001. Agricultural intensification and the collapse of Europe’s farmland bird populations. Proceedings of the Royal Society of London, Series B Biological Sciences 268, 25–29. Donald, P.F., Evans, A.D., Muirhead, L.B., Buckingham, D.L., Kirby, W.B., Schmitt, S.I.A., 2002. Survival rates, causes of failure and productivity of Skylark Alauda arvensis nests on lowland farmland. Ibis 144, 652–664. European Community, 1997. Agenda 2000, Vol. 1: For a Stronger and Wider EU. Office for Official Publications of the European Communities, Luxembourg. European Union, 2005. Agri-Environment Measures – Overview on General Principles, Types of Measures, and Application, European Commission. Directorate General for Agriculture and Rural Development.