There was no difference in the number of birds recorded from the ex-arable SRC plots compared with the ex-grassland SRC plots across all SRC study plots (including data from both plot interiors and edge zones, F1,20 = 1.87, P = 0.187). Combining all SRC plots, the SRC held more birds (3.1 ± 0.2 birds recorded per hectare surveyed overall) than the arable and grassland controls in which we encountered 0.8 ± 0.03 and 1.63 ± 0.02 birds per hectare, respectively (combining controls, t21 = 6.23; P < 0.001). On the grassland controls, corvids were frequently recorded in small flocks, with a maximum count of 12.8 birds recorded per hectare surveyed. The number of birds recorded on the grassland, excluding corvids, was 1.08 ± 0.15 birds per hectare.
In total, 37 species were recorded from within the SRC plots; 32 from ex-arable SRC compared with 21 species from the arable controls (mean species per count area was significantly different, t11 = 3.60, P < 0.005) and 28 from ex-grassland compared with 16 species from the grassland controls (not significantly different t7 = 0.73, P > 0.1). Of the 37 species, 11 were recorded from the SRC plots in every year of the study, the most frequently recorded species being Willow Warbler Phylloscopus trochilus (present in 37% of all point counts from established SRC), Chaffinch Fringilla coelebs (22% of point counts), Blackbird Turdus merula (16%), Blue Tit Parus caeruleus (11%), Reed Bunting Emberiza schoeniclus (8%) and Wren (8%). In the arable controls, only two species (Skylark and Yellow Wagtail) were recorded in every year of the study. Skylarks were the most frequently recorded species from the arable and grass controls (11% and 6% of point counts, respectively). Five species were recorded from the grassland controls during each year of the study (Blackbird, Woodpigeon Columba palumbus, Skylark, Carrion Crow Corvus corone and Rook Corvus frugilegus).
Cut or recently planted SRC
More individuals (t11 = 4.19, P < 0.001) and more species per point count (t11 = 4.46, P < 0.005) were recorded in the edge-zone (cropped area within 50 m of the edge) of recently planted and cut-back SRC on arable land than the edge-zone of the arable controls. Counts in the edge zone of the grassland SRC also recorded more birds than the edge-zone of the grassland controls (t7 = 2.41 P < 0.05).
Combining the edge-zone and interior counts, more individuals of most bird groupings, including waders, were recorded in the recently planted or cut back ex-arable SRC than in their paired arable controls (Table 1, see also Fig. 1). Four species of wader were recorded from these open SRC plots: Lapwing Vanellus vanellus; Redshank Tringa totanus; Curlew Numenius arquata and Oystercatcher Haematopus ostralegus. On ex-grassland sites however, only finches were recorded in greater numbers in recently planted or cut back SRC plots, when compared with controls.
Table 1. Number of birds recorded per hectare surveyed, and number of species per point count, within recently planted and cut back SRC and arable and grassland controls in spring. Note that with the exception of one plot, all the ex-grassland SRC plots were already established, and only 7 were harvested during the study (giving n = 8).
| ||Ex-grass SRC n = 8||Grassland n = 10||t7||P (grass)||Ex-arable SRC n = 12||Arable n = 12||t11||P (arable)||t19||P (total)|
|Buntings||0.32 ± 0.14||0||2.33||ns||0.06 ± 0.03||0.05 ± 0.02||0.14||ns||2.12||ns|
|Skylarks||0.30 ± 0.22||0.09 ± 0.06||0.98||ns||0.31 ± 0.07||0.25 ± 0.04||3.29||*||2.78||*|
|Waders||0.24 ± 0.12||0.12 ± 0.05||1.65||ns||0.86 ± 0.25||0.04 ± 0.02||3.92||**||4.01||***|
|Finches||0.36 ± 0.14||0.01 ± 0.01||2.72||*||0.52 ± 0.18||0.09 ± 0.03||2.45||*||3.58||**|
|Corvids||0.87 ± 0.52||0.61 ± 0.45||0.43||ns||0.01 ± 0.01||0||1.00||ns||0.40||ns|
|Total birds||2.89 ± 0.43||1.18 ± 0.48||1.97||ns||2.71 ± 0.44||0.81 ± 0.09||4.64||**||4.71||***|
|Total species||0.93 ± 0.20||0.46 ± 0.15||1.84||ns||0.58 ± 0.08||0.25 ± 0.02||5.93||***||4.95||***|
Figure 1. The number of birds recorded per hectare of control and SRC plots (data from edge-zone and interior plots combined) on ex-arable land in spring in the early stages of SRC establishment (year 1). Data are from (i) arable controls (n = 12) (ii) recently planted SRC plots on ex-arable (n = 6) and (iii) SRC plots cut back after one years initial growth on ex-arable (n = 6).
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More thrushes, finches, buntings, migrant warblers, gamebirds and other passerines were recorded in the edge-zone of the standing (> 1 year's growth) SRC crop than the edge-zone of the controls (Table 2). In the interior of the standing SRC crop, more finches, tits, buntings, other passerines and migrant warblers were recorded than in the interior of the controls (Table 2). Virtually no Skylarks or waders were recorded from standing SRC plots. More waders were recorded in the interior of the controls than in the interior of standing SRC (t21 = 2.50, P < 0.05). The boundary of the SRC tended to be more attractive to birds than the boundary of the controls with more thrushes, tits, migrant warblers and other passerines (Table 2).
Table 2. Results of analysis comparing number of birds per hectare of boundary, edge and interior of established SRC plots compared with the boundary, edge and interior of arable and grassland controls in spring.
|t21||P|| ||t21||P|| ||t21||P|| |
|Wren, Robin, Dunnock||4.60||***||+||6.70||***||+||3.49||**||+|
|Waders||0.15||ns|| ||1.56||ns|| ||2.50||*||–|
The numbers of birds in the edge-zone SRC plots increased in the first year of willow growth compared with cut-back plots (F1,13 = 5.53, P < 0.05). There was no similar increase in the interior of the SRC plots. After the first year of growth the number of birds recorded within the SRC interior declined (F2,30 = 3.84, P < 0.05). Consequently, there were higher numbers of birds recorded in the edge-zone of SRC plots with 1 year's growth (t17 = 2.59, P < 0.05), and with more than 1 year of growth (t21 = 8.95, P < 0001), than in the interior (Fig. 2). Considering groups, in SRC with more than 1 year's growth, more finches (t21 = 5.06, P < 0.001), thrushes (t21 = 5.76, P < 0.001), tits (t21 = 4.18, P = 0.001), buntings (t21 = 3.76, P < 0.001), migrant warblers (t21 = 4.08, P < 0.001) and gamebirds (t21 = 3.34, P < 0.005) were recorded in the crop edge-zones than in the crop interior.
Figure 2. The number of birds recorded per hectare in spring at various stages of growth in both the edge-zone and interior of the 22 SRC plantations.
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The boundary of SRC crops with less than 2 years’ growth had more finches (t20 = 5.68, P < 0.001), thrushes (t20 = 4.42, P < 0.001), tits (t20 = 7.06, P < 0.001) and other passerines (t20 = 8.64, P < 0.001) recorded than in the edge-zone of the SRC crop. The number of migrant warblers and gamebirds did not differ between these two areas of the SRC plots. In contrast, the edge-zone of SRC plots with 2 or more years of willow growth had similar numbers of finches, thrushes, tits and buntings to the surrounding boundary; and more migrant warblers (t20 = 4.26, P < 0.001) and gamebirds (t20 = 2.17, P < 0.001). In these established plots only other passerines were still encountered more frequently in the boundary than the SRC edge-zone (t20 = 4.30, P < 0.001).
Different species of birds were associated with different age classes of willow. Within established SRC, tits reached maximum numbers in 2-year-old coppice compared with other age-classes (F2,26 = 3.84, P < 0.05) and other passerines in 3-year-old coppice (F2,26 = 4.34, P < 0.05). The numbers of migrant warblers (F1,14 = 5.69, P < 0.05) and thrushes (F1,14 = 7.58, P < 0.05) increased in the second year of willow growth (between 1-year-old and 2-year-old coppice), and remained fairly high subsequently.
In the winter, 47 species of birds were recorded within the SRC plots, 42 in the ex-arable SRC and 43 in the ex-grass. While there were only 24 species recorded overall in the grassland controls and 39 in the arable controls, there were more species per plot per visit in the grass fields (4.85 ± 0.30) than in the arable fields (2.15 ± 0.25). Overall, more species were encountered in the ex-arable and ex-grassland SRC plots combined (6.57 ± 0.27) than in their paired controls (t21 = 8.31, P < 0.001). The most commonly recorded birds on the grassland controls were thrushes and corvids, with occasional flocks of Rooks, Fieldfares Turdus pilaris and Redwings Turdus iliacus. There were more corvids on the grassland fields than either the arable fields (F1,20 = 13.50, P < 0.005) or the established ex-grassland SRC plots (t9 = 4.07, P < 0.005). The most abundant bird in the arable controls was the Woodpigeon, with flocks of over 100 birds on three occasions. The most commonly recorded bird in the SRC was Chaffinch, with a maximum count of 90 individuals. The SRC plots planted on grassland attracted similar birds to those found in SRC plots planted on arable land, although there were more tits (F1,20 = 19.81, P < 0.001) in the ex-grassland plots.
Just planted or recently cut coppice on arable land had higher numbers of buntings (t8 = 2.48, P < 0.05), thrushes (t8 = 2.31, P < 0.05) and other passerines (t8 = 3.01, P < 0.05) recorded in winter than the arable plots. Buntings were especially abundant in the just-cut coppice with maximum counts of 59 Yellowhammers Emberiza citrinella and 35 Reed Buntings. Skylarks were more abundant in the arable controls with a maximum flock size of 32 (t11 = 2.36, P < 0.05). Recently planted or cut coppice supported fewer tits than established coppice (F1,14 = 14.78, P < 0.005). The recently planted coppice tended to be more attractive to waders than the established plots. The recently planted coppice on grassland and the few ex-grassland plots that had been harvested did not differ from their grassland control plots. Overall, more gamebirds were recorded on the just planted and recently cut coppice than on the grassland and arable controls (t11 = 4.42, P < 0.005).
Finches (t21 = 2.82, P < 0.05), buntings (t21 = 4.99, P < 0.001), tits (t21 = 7.32, P < 0.001), other passerines (t21 = 4.71, P < 0.001) and gamebirds (t21 = 4.50, P < 0.001) were all more commonly encountered in winter in the established SRC plots than the controls. The number of thrushes in the SRC was similar to that found in the controls. However, there were more thrushes in the ex-arable SRC plots than the arable controls (t11 = 4.42, P < 0.005).
Although waders overall were recorded equally in the SRC and in the controls, there were species differences. Snipe Gallinago gallinago was the most frequently recorded wader wintering in SRC plots, and was recorded from nine of the 12 plots planted on arable land and from one plot planted on grassland. Maximum counts were recorded in November and December of year 2, when a total of 87 birds were counted over the two visits. Snipe were also recorded from five arable control plots and one grassland control. There was an average of 0.32 ± 0.19 Snipe in control plots compared with 0.98 ± 0.44 Snipe in SRC. Woodcock Scolopax rusticola was also frequently flushed from both established and recently cut SRC and was more abundant in SRC than the controls (t21 = 5.90, P < 0.001) where it was only recorded once. Lapwings were more abundant in the controls (t21= 2.40, P < 0.05) with a maximum flock of 32 birds. Only one Lapwing was recorded from a SRC plot. Golden Plover Pluvialis apricaria were also recorded from an arable control field on two occasions but not from the SRC. A flock of 22 Curlew was recorded on one occasion in a recently cut SRC ex-grassland plot, but were never recorded from the controls.