Mark H. Hancock

Recent changes in the abundance of British upland breeding birds

Capsule Breeding wader populations have more often shown declines than passerine populations during the last 10–20 years. Aims To determine abundance changes in British upland breeding birds during the last 10–20 years. Methods We re-surveyed 1348 km2, in nine study areas, of the British uplands in 2000 and 2002, which had been previously surveyed between 1980 and 1991. In addition, we included data from recent repeat surveys in four other upland areas, covering approximately 365 km2, to broaden the scope of our study. Results We found evidence of widespread population declines in three species of breeding waders, Lapwing Vanellus vanellus, Dunlin Calidris alpina and Curlew Numenius arquata. Among the passerines, some species declined, including Twite Carduelis flavirostris and Ring Ouzel Turdus torquatus, while others showed strong gains, including Stonechat Saxicola torquata and Raven Corvus corax. Conclusion Overall, abundance changes were characterized by a high degree of variability across study areas, even when close together. This variability may have been partly due to the different time intervals between the original and repeat surveys. Improved upland breeding bird population monitoring is needed to allow better detection of trends. Action is needed to restore upland breeding bird populations in areas where they have declined.

Winter habitat associations of seed-eating passerines on Scottish farmland

CapsuleExtensive surveys highlighted the importance of weedy fodder brassicas, stubbles and open farmland landscapes to declining birds. Aims To determine habitat associations of seed-eating passerines on Scottish farmland in winter, and recommend appropriate conservation measures. Methods Transect surveys were carried out on farmland in 100 1-km squares, containing 2885 fields, across Scotland. Birds, crops, field boundary features and weeds were recorded on three visits. Bird–habitat associations were examined using logistic regression models. Results Seed-eating passerines were highly concentrated: 100 fields (1.4% of the area surveyed) held half the total count. The highest field densities of birds were recorded in fodder brassica crops and stubbles, averaging 12 and 3.3 birds/ha respectively. In fodder crops, weedier fields held many more birds. Multiple regression analysis emphasized the importance of fodder crops, stubbles and farmyards and suggested that declining bird species preferred more open landscapes. Several bird species were associated with fields containing very weedy patches, and/or weeds of the family Chenopodiaceae. These features were commonest in fodder brassicas. Many of the crop types found to be important as bird habitats in winter have declined in area in Scotland; the availability of seed food in such habitats may also have diminished. Such changes may partly explain recent population declines. Conclusions Agri-environment measures for seed-eating passerines should support the widespread provision of small areas of seed-rich wintering habitats, such as weedy fodder brassicas and stubbles, especially in open (0–10% woodland and scrub) landscapes in areas with mild winters.

Modelling edge effects of mature forest plantations on peatland waders informs landscape-scale conservation

Summary 1. Edge effects of native forest fragmentation have been well studied, but there are few studies of open-ground habitats fragmented by plantation forests. We measure forestry edge effects on open-ground breeding birds, following one of Europe’s biggest and most controversial land-use transformations. 2. The ‘Flow Country’ of northern Scotland is one of the world’s greatest expanses of blanket bog. It became fragmented by conifer forests planted in the late 20th century, and these now adjoin open peatlands protected under European conservation legislation. Detrimental edge effects on breeding birds were anticipated, but not apparent shortly after planting. 3. Using survey data collected in 2003–2006, and logistic regression modelling, we tested whether breeding distributions of three wader species of international conservation concern, dunlin, European golden plover and common greenshank, were influenced by distance to forest edge, controlling for habitat and topography. 4. All three species were more likely to occupy flatter, more exposed ground close to bog pools and were influenced by peatland vegetation structure. There was an additive and adverse effect of proximity to forest edge for dunlin and European golden plover, but not common greenshank. This effect was strongest within 700 m of forest edges. We used these results to predict which areas should benefit most from removal of adjacent forestry and so guide maintenance and restoration of the bird interests of the protected areas. 5. Synthesis and applications. Edge effects of mature forestry on dunlin and golden plover are apparent over several hundred metres and are now being used to guide forest planning in northern Scotland. The scale of edge effect is broadly consistent with other avian studies in open-ground habitats across Eurasia and North America, so buffer zones of this order are consistent with possible impacts of plantation forestry on open-ground habitats of bird conservation interest. Given renewed interest in conifer afforestation as a climate change mitigation measure, an improved understanding of edge effects and the mechanisms through which they operate is vital to managing plantation forestry in ways that maintain open-ground landscapes of high conservation value.

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.

An exceptional Calluna vulgaris winter die-back event, Abernethy Forest, Scottish Highlands

Background: Calluna vulgaris is a woody shrub forming plant communities of economic and international conservation importance. Following winter 2002–2003, there was exceptional Calluna die-back in the central Scottish Highlands. Aim: To understand the effects and causes of this die-back event at Abernethy Forest Nature Reserve, Cairngorms National Park. Methods: Patterns of weather, foliage moisture and microclimate were interpreted in relation to patterns of Calluna vulgaris die-back. Vegetation development was investigated over 4 years, based on pre-existing monitoring plots. Results: February 2003 included a period of exceptionally low air humidity, during which unusually low Calluna shoot moisture readings were made, particularly in areas that subsequently had severe die-back. In monitored areas, Calluna cover declined by a third, with minimal recovery after three growing seasons. Die-back was more severe where Calluna was longer-stemmed and less abundant, and where topography was flatter or more north-facing. These topographical features, and die-back, were correlated with colder winter microclimates. A doubling in Vaccinium myrtillus cover in forest plots was strongly correlated with the pattern of Calluna die-back. Meteorological data showed an eight-fold increase in the variability of winter humidity minima since 1983–1984. Conclusions: Die-back probably followed severe ‘winter desiccation’, caused by extreme low humidity conditions, combined with low temperatures, lack of snow cover, and Calluna vulnerability due to age. It led to a major vegetation change in the direction of management aims at this site, but contrary to aims at many other Calluna-dominated sites. The importance of climatic variability as a potential driver of major vegetation change is emphasised.

Associations between distance to forest and spatial and temporal variation in abundance of key peatland breeding bird species

Capsule Negative forest edge effects were detected for Willow Ptarmigan (Red Grouse) Lagopus lagopus and Dunlin Calidris alpina. Aims To investigate the effects of distance to forest on the abundance and changes in abundance of four key peatland breeding bird species, and to measure changes in predatory bird numbers, in the peatlands of northern Scotland. Methods Bird surveys were carried out in 2000 at 34 plots, covering 197 km2 of peatland, and 80 forestry point‐count sites, first surveyed in 1988. Habitat data were also collected in 2000. We used multi‐model inference to investigate the associations between forest distance and other habitat variables, and the abundance, and changes in abundance, of four bird species of economic or conservation importance: Red Grouse, European Golden Plover Pluvialis apricaria, Dunlin and Common Greenshank Tringa nebularia. Results There was strong evidence that distance to forest was negatively associated with Dunlin abundance and changes in Red Grouse abundance, but only weak evidence for negative associations with Golden Plover abundance and changes in Dunlin abundance. There was no evidence of a forest distance effect on Greenshank. Among predatory birds, there were no significant increases either on peatland plots or in new forestry plantations. Conclusions This study provides evidence that, for a given habitat quality, Dunlin densities are lower, and Red Grouse declines more likely, near to forest edges, but weak evidence only that Dunlin declines are more likely, and Golden Plover abundance lower, near to forests. These results suggest that for at least two key peatland breeding birds, forest removal is likely to benefit birds breeding on adjacent unafforested peatland.

Correlates of Breeding Success of Horned Grebes in Scotland

Abstract. A study was carried out on breeding Horned (Slavonian) Grebes (Podiceps auritus) in Scotland to investigate causes of low breeding success. Clutch and brood survival were examined separately, as well as overall breeding success. For those clutches where the cause of loss was known, most were lost to avian predators. Clutch survival was negatively correlated with crow (Corvus spp.) frequency and variability in water levels. Brood survival was lower where the introduced fish species, Pike (Esox lucius) was present and higher where the water was clearer. These factors may have affected predation rates and foraging efficiency, respectively. Overall productivity (young fledged per pair) was negatively related to the frequency of crows and number of bank anglers, who can disturb grebes. Remains of 19 fully-grown birds were found at five lakes. Some had been skinned and dismembered in a similar way, suggesting predation by a mustelid. Steps to improve productivity should include education of bank anglers, and perhaps selective removal of Pike and crows. Alternatively, breeding habitat could be improved at lakes where predators are less common.

Diversity and stability of ericaceous shrub cover during two disturbance experiments: one on heathland and one in forest

Abstract Background: Accumulating evidence, mainly from small-scale experiments, suggests that species diversity helps stabilise ecological communities; however, this relationship needs testing at larger scales in a wider range of natural communities. Aims: In experimentally burnt ericaceous shrub stands, we aimed to determine whether more diverse stands had more stable vegetation cover. Methods: Using two prescribed fire management experiments – one on heathland and one in forest – at scales of 100–700 m2, we compared pre-disturbance vegetation characteristics (measures of diversity, traits and composition) with resistance (degree of perturbation on disturbance), resilience (here defined as post-disturbance recovery rate) and stability (the inverse of temporal variability). Results: Responses to disturbance were usually best explained by a measure of dominance: Simpsons index. High dominance was associated with high resilience, but low resistance and low stability. Within the forest, the shrub community had lower dominance and higher stability than it did on heathland. Dominance and diversity were strongly linked as opposite poles of a principal axis of vegetation variation; therefore, more diverse vegetation was more stable. Conclusions: Ericaceous shrub cover is known to support important ecosystem services, such as soil protection, carbon sequestration, flood prevention and livestock grazing. Our results suggest that high shrub diversity would support stable provision of these services. Land managers who prioritise this aim in British heathlands and pinewoods should consider a wider range of management approaches than those of typical current practice.

Provisioning of Slavonian Grebe Podiceps auritus chicks at nests in Scotland

Capsule Slavonian Grebe nests are used as a focal point for feeding chicks in the early stages of growth, with considerable variation in feeding rates diurnally and across the duration of post‐hatch nest use.

Habitat associations of young Black Grouse Tetrao tetrix broods

ABSTRACT Capsule: In the Scottish Highlands, Black Grouse Tetrao tetrix females with young broods selected areas rich in wet flushes, grasses and Sphagnum mosses. Aims: To identify associations between young Black Grouse broods and habitat characteristics. Methods: We located brood-rearing Black Grouse females in four areas of moorland-forest mosaic in the Scottish Highlands. Each brood was paired with a random reference location 100 m away. We recorded cover of different habitats and fine-scale vegetation and structure within squares of 1 and 0.25 ha, respectively. Associations between brood occurrence and habitat and vegetation variables were examined at the two scales. Results: Black Grouse broods were positively associated with wet flushes (1 ha), and with Heather Calluna vulgaris, sedges Carex spp., grasses, Sphagnum mosses and taller vegetation with intermediate levels of height variability (0.25 ha). Conclusions: This study highlights the importance of wet habitats for young Black Grouse chicks. In addition, relatively tall field-layer vegetation comprising Heather, sedges, grasses over a layer of Sphagnum mosses attracted brood-rearing Black Grouse females. Many management practices associated with peatland restoration, including drain-blocking, Sphagnum re-establishment and the avoidance of burning on deep peat soils, are therefore consistent with favourable habitat management for Black Grouse.