Allan J. Perkins

Habitat characteristics affecting use of lowland agricultural grassland by birds in winter

Almost a third of the bird species designated as Species of European Conservation Concern exploit agricultural grasslands, yet few studies have focused on their use as foraging habitats for birds. This study investigated the influence of variation in sward structure, grassland management and landscape variables on the use of 77 grass fields by 14 field-feeding bird species wintering on lowland mixed farmland in southern England. Multiple logistic regression was used to model the proportion of bird-count visits in which each species was encountered as a function of the recorded habitat variables for each field. Variation in sward height and density were associated with frequency of occurrence for 12 bird species and larger areas of bare earth and occurrence of winter grazing by stock animals were correlated with greater frequency of occurrence by 11 bird species. Two rapidly declining species, skylark (Alauda arvensis) and yellowhammer (Emberiza citrinella), were recorded more frequently on fields with higher numbers of seeding grasses. We suggest that mosaics of fields managed as short-term leys and permanent pastures with low-intensity cattle grazing over the autumn and winter would provide the combination of heterogeneous sward structure, areas of bare earth and presence of some seeding plants necessary to maximise the range of bird species able to use a given area of agriculturally improved grassland throughout the winter.

Use of field margins by foraging yellowhammers Emberiza citrinella

Abstract Some agri-environment schemes promote the creation and management of a variety of non-crop habitats on farmland in the UK, yet there has been relatively little monitoring to assess how species, particularly birds, use these habitats. The present study deals with a declining UK farmland bird species, yellowhammer Emberiza citrinella , and considers to what extent grass margins of arable fields are used as a foraging habitat when feeding nestlings. Studies were carried out in lowland mixed farmland in southern England. Grass margins and other non-crop field boundary habitats, such as hedgerows and ditches, were selected relative to cropped areas by yellowhammers. No significant difference was found between use of cut and uncut grass margins. Studies have shown that grass margins support high densities of invertebrates and their provision at the edge of arable fields would benefit yellowhammers during the breeding season both as habitat for prey and as nesting habitat. During the breeding season from May to August, management should create cut and uncut grass margins in close proximity to each other. This could be achieved by cutting only the outer edge of the grass margin, maintaining cover next to the hedgerow. Cut areas would provide easier access to food resources for birds and prevent weed encroachment to the crop, whilst adjacent uncut areas would maintain invertebrate sources and provide nesting cover for yellowhammers.

Microsatellite variation in the yellowhammer Emberiza citrinella: population structure of a declining farmland bird

In recent years, there has been much concern in the UK about population declines of widespread species in agricultural habitats. Conservation‐orientated research on declining birds has focused on vital rates of survival and productivity. However, the environmental factors which may influence movements between populations of widespread species is poorly understood. Population genetic structure is an indirect description of dispersal between groups of individuals. To attempt to develop an understanding of genetic structuring in a widespread, but declining, farmland bird, we therefore investigated the yellowhammer, Emberiza citrinella, population in England and Wales using microsatellite data. Our first aim was to investigate whether there was genetic substructuring in the population. A second aim was to investigate if there was a relationship between genetic distances and various environmental variables. Finally, we analysed the microsatellite data for evidence of loss of genetic variation due to population decline. Our data showed a slight but significant structure within the yellowhammer population. This therefore cannot be considered a panmictic population. Our example from South Cumbria implies that high‐altitude barriers may have a slight influence on population structure. However, on the whole, genetic distances between sample sites were not significantly correlated with geographical distances, degrees of population connectivity, high altitudes, or differences in precipitation between sites. Finally, we detected departures from mutation‐drift equilibrium (excess heterozygosity), which is indicative of a loss of genetic variation through recent decline.

Chaffinch Fringilla coelebs foraging patterns, nestling survival and territory distribution on lowland farmland

Numbers of many bird species which breed on farmland, and are reliant on cropped land for feeding or nesting, declined between the 1960s and 1990s. In contrast, Chaffinch Fringilla coelebs numbers increased on farmland over the same period. This study investigates the influence of both cropped and non-cropped land on Chaffinches foraging for nestlings, nestling survival and territory density. The study was carried out on nine mixed lowland farms in south central England in 1996 and 1997. Chaffinches made little use of cropped areas when foraging for young (less than 9% of foraging visits, despite cropped areas covering 93% of study areas). Instead, trees and bushes influenced foraging patterns and breeding success. Extensive use was made of trees and bushes by adults searching for food for nestlings (75% of foraging visits were to hedges and trees within boundaries or fields, despite these areas covering <3% of study areas). Oaks (69% of visits) and Willows (15% of visits) were found to be the most favoured species of tree for foraging. In one year of the study, chick starvation was less frequent in nests located on field boundaries with Oak trees than in nests on boundaries without Oaks. Successful nests also tended to be closer to Oak or Willow trees than those where nestlings starved. Territory density was not related to hedgerow structure, presence or absence of Oaks and Willows in field boundaries, or adjacent cropping. Our findings on nest survival were supported by analysis of British Trust for Ornithology nest record data which revealed that nests associated with trees had better brood survival rates than sites not located close to trees. The use of trees and shrubs for feeding and nesting in the farming landscape and the ability to utilize unkempt hedgerows may have contributed to the ability of Chaffinches to persist on farmland despite wide-scale agricultural change in recent decades.

Use of time-lapse video cameras to determine causes of nest failure of Slavonian Grebes Podiceps auritus

Capsule Few clutches were predated, with Otter Lutra lutra the most frequent predator filmed. Aims To determine the rate of nest predation and identify predators of the Slavonian Grebe Podiceps auritus in Scotland. Methods Miniature 24-hour time-lapse video cameras were placed next to 23 Slavonian Grebe nests on five lakes to record nest failure events and to identify predators that depredated the contents of nests. For comparison, ten nests without cameras were also monitored and their outcomes recorded. Results The probabilities of clutch failure due to predation, and wave damage or water level rise were 19% and 30%, respectively. Otters took two clutches and an adult grebe plus chicks from nests. Other predators filmed at nests were Stoat Mustela erminea, Carrion Crow Corvus corone, Common Gull Larus canus and Coot Fulica atra. No difference in predation rates between nests with and without cameras was detected. Otters were recorded at eight of 13 lakes studied. An American Mink Mustela vison was recorded at one lake. Conclusion The nest predation rate of Slavonian Grebe in Scotland was not high compared with other studies and is not of conservation concern.

Targeted management intervention reduces rate of population decline of Corn Buntings Emberiza calandra in eastern Scotland

Capsule Breeding populations were less likely to decline when farmland was subject to management intervention designed to benefit the species. Aims To determine whether targeted management intervention helps to halt or reverse the decline of Corn Buntings in eastern Scotland. Methods Counts of territorial male Corn Buntings in the breeding seasons of 2002 and 2004 were compared across 53 2-km squares. Nineteen of these were subject to management intervention designed to benefit Corn Buntings, effective from 2003. The other 34 had no such management. For a subset of 44 tetrads, counts in 2000 and 2002 were also compared between the two sets of tetrads. Results Between 2002 and 2004, Corn Bunting numbers showed no significant change in tetrads with targeted management intervention, but declined by 43% in tetrads with no intervention. By contrast, population changes did not differ significantly in these two groups of tetrads between 2000 and 2002, before management was implemented. Conclusion Targeted management intervention was associated with reduced short-term probability of Corn Bunting population decline on farms in eastern Scotland. Management interventions that are designed to provide habitats required by the species have the potential to halt, or perhaps reverse, the Corn Bunting decline in eastern Scotland.

Decline of Corn Buntings Emberiza calandra on east Scottish study areas in 1989-2007

Capsule Adult numbers on many study areas fluctuated from year to year, but overall showed a large decline, down to extinction on most areas. Aims To measure changes in summer numbers of adult Corn Buntings in a large sample of study areas holding discrete localized populations. Methods Singing cocks and hens paired with them were counted in early summer at 30 study areas on farmland from south Angus to central Aberdeenshire. Sixteen populations occurring throughout 1989–95 were called ‘groups’. Counts also included 16 cases where a new ‘offshoot’ appeared in late May or the start of June, not having been seen earlier in that spring or in the previous winter or summer. Results Following relative stability in 1989–95, large declines occurred in 1995–96, 1998–99 and 2003–04, and decreases far outweighed occasional increases between consecutive summers. The numbers of established groups, new offshoots, and older offshoots all declined with the year. Although containing one to nine founding pairs, new offshoots became extinct later, in six cases after one summer. No new offshoot was seen after 1995. Conclusions Although 22 study areas held birds in 1989 and 25 in 1990, this fell to 10 in 1999, seven in 2005, and four in 2007 (the only areas that held birds in all years). On all areas combined, cock numbers fell by 83% between 1989 and 2007. Targeted implementation of appropriate agri‐environment measures is urgently needed to halt and reverse such declines, a challenge made all the greater within the last year by rising grain prices, delays to the introduction of new measures, and abolition of EU ‘set‐aside’ as a means for providing food and nesting habitat.

Crop sward structure explains seasonal variation in nest site selection and informs agri-environment scheme design for a species of high conservation concern: the Corn Bunting Emberiza calandra

Capsule Corn Buntings nested in tall dense grasses and cereals, selecting for sward density over height, and cereal fields with high weed scores. Aims To measure the vegetation attributes of fields selected as nest sites by Corn Buntings, to inform the design of safe nesting habitat measures in agri-environment schemes for this rapidly declining ground-nesting passerine. Methods Nesting activity was monitored across 32 farms in eastern Scotland during 2004–09. Land use and singing males were mapped to measure habitat availability for nesting females within their mates territory, and crop swards measured. Effects of sward characteristics on field selection for nesting, and seasonal variation in crop use, were modelled. Results Nests (95% of 580) were mainly in cereals and grasses. Taller denser swards were selected, with sward density a stronger predictor of field use than sward height, and cereal field use strongly associated with high weed scores. Variation in sward structure between crop types, and changes due to crop maturation or harvesting, largely explained seasonal patterns in crop use. Conclusion Conservation measures targeting nesting Corn Buntings should provide uncut or late-cut grasses or cereals 30–100 cm tall with a dense ground layer of weeds or crop vegetation.

Using dual-sex calls improves the playback census method for a nocturnal burrow-nesting seabird, the Manx Shearwater Puffinus puffinus

ABSTRACT Capsule: Playback with dual-sex calls increases the response rate of Manx Shearwaters Puffinus puffinus by 40–60% and reduces its daily variability, which would improve the precision of population estimates. Aims: To test whether playing male and female calls would elicit more responses to playback than male-only calls, reduce daily variability and the length of response rate calibration trials, and give more precise estimates. We also measured response times to playback and assessed the reliability of visual signs of occupancy at burrow entrances. Methods: Responses to four playback call-types (male-only and three variants of dual-sex calls) were compared in repeated trials at two colonies (Ramsey and Rum, UK) during May–June 2014. Results: Dual-sex calls gave higher response rates with lower variance than male-only calls, because females frequently replied to female calls but rarely to male calls. In simulated 3–5-day calibration trials, response rates and correction factors were up to 50% more precise with dual-sex calls. Visual signs of burrow occupancy were unreliable. Conclusion: Playback for Manx Shearwaters should use a 25 seconds recording of male and female calls intermixed, with 10 seconds listening time for delayed responses. Census-specific calibration trials are essential for accurate estimates of daily response rates.