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Crop diversity loss as primary cause of grey partridge and common pheasant decline in Lower Saxony, Germany

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ABSTRACT

Background: The grey partridge (Perdix perdix) and the common pheasant (Phasianus colchicus) are galliform birds typical of arable lands in Central Europe and exhibit a partly dramatic negative population trend. In order to understand general habitat preferences we modelled grey partridge and common pheasant densities over the entire range of Lower Saxony. Spatially explicit developments in bird densities were modelled using spatially explicit trends of crop cultivation. Pheasant and grey partridge densities counted annually by over 8000 hunting district holders over 10 years in a range of 3.7 Mio ha constitute a unique dataset (wildlife survey of Lower Saxony). Data on main landscape groups, functional groups of agricultural crops (consisting of 9.5 million fields compiled by the Integrated Administration and Control System) and landscape features were aggregated to 420 municipalities. To model linear 8 or 10 year population trends (for common pheasant and grey partridge respectively) we use rho correlation coefficients of densities, but also rho coefficients of agricultural crops.

Results: All models confirm a dramatic decline in population densities. The habitat model for the grey partridge shows avoidance of municipalities with a high proportion of woodland and water areas, but a preference for areas with a high proportion of winter grains and high crop diversity. The trend model confirms these findings with a linear positive effect of diversity on grey partridge population development. Similarly, the pheasant avoids wooded areas but showed some preference for municipalities with open water. The effect of maize was found to be positive at medium densities, but negative at very high proportions. Winter grains, landscape features and high crop diversity are favorable. The positive effect of winter grains and higher crop diversity is also supported by the trend model.

Conclusions: The results show the strong importance of diverse crop cultivation. Most incentives favor the cultivation of specific crops, which results in large areas of monocultures. The results confirm the importance of sustainable agricultural policies.

Electronic supplementary material: The online version of this article (doi:10.1186/s12898-016-0093-9) contains supplementary material, which is available to authorized users.

No MeSH data available.


Minimum adequate habitat model of grey partridge breeding pairs. Figure displays results of GAMM showing significant smoothers: a winter grain (%) agricultural land, b mean field block size, c Shannon Index, d % forest/municipal area, e % open water/municipal area, f longitude × latitude. R2 adjusted = 0.48
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Fig4: Minimum adequate habitat model of grey partridge breeding pairs. Figure displays results of GAMM showing significant smoothers: a winter grain (%) agricultural land, b mean field block size, c Shannon Index, d % forest/municipal area, e % open water/municipal area, f longitude × latitude. R2 adjusted = 0.48

Mentions: The minimum adequate model for the habitat model of grey partridge breeding pairs underlines the dramatic loss in grey partridge abundance, with all years, except for 2006, having significantly lower densities than 2005 (Table 1, p < 0.001). When percentages of winter grain are <20 %, grey partridges are less abundant. In municipalities with higher proportions the model shows overall positive responses, however when it is above 55 %, the effect is non-significant and the standard error gets larger (Fig. 4a). The non-significant smoother for field block size should not be overestimated; nonetheless it improves model fit and vaguely points to a preference of relatively large field blocks of >6 ha (Fig. 4b). As the second most important smoother (Table 1; F = 20.7, p < 0.001) for crop diversity per municipality, the Shannon index shows that highly diverse municipalities are of benefit for the grey partridge (Fig. 4c). The grey partridge is rare in areas with a high proportion of forest/woodland, which is at the same time the most important coefficient (Table 1; F = 35.6, p < 0.001), and also a negative response to water expanse (Fig. 4 d, e). The tensor product of longitude by latitude shows the high density areas in central Lower Saxony and the lower abundances in the north and the south (Fig. 4f). The model with R2 adjusted at 0.48 explains roughly half the variance.Table 1


Crop diversity loss as primary cause of grey partridge and common pheasant decline in Lower Saxony, Germany
Minimum adequate habitat model of grey partridge breeding pairs. Figure displays results of GAMM showing significant smoothers: a winter grain (%) agricultural land, b mean field block size, c Shannon Index, d % forest/municipal area, e % open water/municipal area, f longitude × latitude. R2 adjusted = 0.48
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5016946&req=5

Fig4: Minimum adequate habitat model of grey partridge breeding pairs. Figure displays results of GAMM showing significant smoothers: a winter grain (%) agricultural land, b mean field block size, c Shannon Index, d % forest/municipal area, e % open water/municipal area, f longitude × latitude. R2 adjusted = 0.48
Mentions: The minimum adequate model for the habitat model of grey partridge breeding pairs underlines the dramatic loss in grey partridge abundance, with all years, except for 2006, having significantly lower densities than 2005 (Table 1, p < 0.001). When percentages of winter grain are <20 %, grey partridges are less abundant. In municipalities with higher proportions the model shows overall positive responses, however when it is above 55 %, the effect is non-significant and the standard error gets larger (Fig. 4a). The non-significant smoother for field block size should not be overestimated; nonetheless it improves model fit and vaguely points to a preference of relatively large field blocks of >6 ha (Fig. 4b). As the second most important smoother (Table 1; F = 20.7, p < 0.001) for crop diversity per municipality, the Shannon index shows that highly diverse municipalities are of benefit for the grey partridge (Fig. 4c). The grey partridge is rare in areas with a high proportion of forest/woodland, which is at the same time the most important coefficient (Table 1; F = 35.6, p < 0.001), and also a negative response to water expanse (Fig. 4 d, e). The tensor product of longitude by latitude shows the high density areas in central Lower Saxony and the lower abundances in the north and the south (Fig. 4f). The model with R2 adjusted at 0.48 explains roughly half the variance.Table 1

View Article: PubMed Central - PubMed

ABSTRACT

Background: The grey partridge (Perdix perdix) and the common pheasant (Phasianus colchicus) are galliform birds typical of arable lands in Central Europe and exhibit a partly dramatic negative population trend. In order to understand general habitat preferences we modelled grey partridge and common pheasant densities over the entire range of Lower Saxony. Spatially explicit developments in bird densities were modelled using spatially explicit trends of crop cultivation. Pheasant and grey partridge densities counted annually by over 8000 hunting district holders over 10&nbsp;years in a range of 3.7&nbsp;Mio&nbsp;ha constitute a unique dataset (wildlife survey of Lower Saxony). Data on main landscape groups, functional groups of agricultural crops (consisting of 9.5 million fields compiled by the Integrated Administration and Control System) and landscape features were aggregated to 420 municipalities. To model linear 8 or 10&nbsp;year population trends (for common pheasant and grey partridge respectively) we use rho correlation coefficients of densities, but also rho coefficients of agricultural crops.

Results: All models confirm a dramatic decline in population densities. The habitat model for the grey partridge shows avoidance of municipalities with a high proportion of woodland and water areas, but a preference for areas with a high proportion of winter grains and high crop diversity. The trend model confirms these findings with a linear positive effect of diversity on grey partridge population development. Similarly, the pheasant avoids wooded areas but showed some preference for municipalities with open water. The effect of maize was found to be positive at medium densities, but negative at very high proportions. Winter grains, landscape features and high crop diversity are favorable. The positive effect of winter grains and higher crop diversity is also supported by the trend model.

Conclusions: The results show the strong importance of diverse crop cultivation. Most incentives favor the cultivation of specific crops, which results in large areas of monocultures. The results confirm the importance of sustainable agricultural policies.

Electronic supplementary material: The online version of this article (doi:10.1186/s12898-016-0093-9) contains supplementary material, which is available to authorized users.

No MeSH data available.