Murray C. Grant

Relationships between bird abundance and the composition and structure of moorland vegetation

Capsule Variations in the composition, structure and heterogeneity of moorland vegetation are shown to affect the abundance of eight of nine moorland bird species, with implications for grazing management. Aims To determine how variation in vegetation characteristics affects breeding bird abundance on moorlands. Methods Bird and habitat data from 85 2-km2 plots in south Scotland and northern England were analysed using multivariate analysis to disentangle vegetation effects from confounding site and management effects. Results Of nine species studied in detail, Red Grouse Lagopus lagopus scoticus and Stonechat Saxicola torquata were associated with Heather Calluna vulgaris, although both favoured some heterogeneity in cover. Meadow Pipit Anthus pratensis demonstrated a curvilinear relationship with Heather cover, whilst both Curlew Numenius arquata and Snipe Gallinago gallinago were most abundant where vegetation structure was relatively heterogeneous. Skylark Alauda arvensis and Golden Plover Pluvialis apricaria were positively associated with short vegetation, in particular short grass and short dwarf shrub cover, respectively. Whinchat Saxicola rubetra was associated with dense vegetation, particularly Bracken Pteridium aquilinum, but no strong vegetation effects were detected for Wheatear Oenanthe oenanthe. Six of the nine species showed positive associations with vegetation typical of wet conditions. Conclusions Moorland birds vary in their preferences for particular compositional and structural vegetation features, and management promoting heterogeneity and wetland vegetation is likely to support a diverse bird community and benefit certain key species. Losses of Heather cover in recent decades, primarily from increased grazing levels, appear likely to have reduced habitat availability for only two of the nine species studied.

Characterizing demographic variation and contributions to population growth rate in a declining population

1. Understanding how demographic variation translates into variation in population growth rate (λ) is central to understanding population dynamics. Such understanding ideally requires knowledge of the mean, variance and covariance among all demographic rates, allowing the potential and realized contribution of each rate to λ to be estimated. Such studies require integrated monitoring of all demographic rates across multiple years and are consequently rare, particularly in declining populations and for species with less tractable life histories. 2. We used 12 years of comprehensive demographic data from a declining ring ouzel (Turdus torquatus) population to estimate the mean, variance and covariance in all major demographic rates and estimate potential and realized demographic contributions to λ. 3. Population size decreased from 39 to 13 breeding pairs (-67%) and mean λ was 0·91 during 1998-2009. This decrease did not reflect a substantial concurrent decrease in any single key demographic rate, but reflected varying combinations of demographic rates that consistently produced λ < 1. 4. Basic prospective elasticity analysis indicated that λ was most sensitive to adult survival, closely followed by early season reproductive success and early brood first-year survival. In contrast, integrated elasticity analysis, accounting for estimated demographic covariance, indicated that λ was most sensitive to early brood first-year survival, closely followed by re-nesting rate, early season reproductive success, late-brood first-year survival and adult survival. 5. Retrospective decomposition of variance suggested that first-year survival contributed most to observed variation in λ. 6. However, demographic comparison with other related species suggested that adult survival, but not reproductive success or post-fledging survival, averaged lower than expected throughout the 12-year study. 7. These data demonstrate that multiple approaches, including comprehensive demographic and comparative analyses and due consideration of conflicting answers, may be necessary to accurately diagnose the demographic basis of population change.

Exploring the relationships between wader declines and current land-use in the British uplands

Capsule Declines of upland waders were associated with habitat cover, forest edge exposure, grouse moor management intensity and crow abundance. Aims To explore whether changes in the abundance of five wader species in the uplands correlate with the three key hypotheses proposed for their declines. Methods Using data from repeat upland bird surveys, we examined at two spatial scales (region and plot) if population changes correlate with vegetation cover, forest edge exposure, grouse moor management intensity or crow abundance. Results For Northern Lapwings Vanellus vanellus and Eurasian Curlews Numenius arquata, there was an association between declines and broad‐scale vegetation cover; declines being greatest on heather‐dominated plots. Exposure to forest edge was associated with declines of European Golden Plovers Pluvialis apricaria and Common Snipe Galinago galinago at the plot scale, and of Northern Lapwings at the regional scale. More intensive grouse moor management was associated with lower declines in Northern Lapwings at both the plot and regional scale, but with greater declines in European Golden Plovers at the plot scale. Northern Lapwings also declined most on plots with the highest Carrion Crow Corvus corone abundance. Conclusion These analyses represent the first attempt to assess empirically the balance of evidence for different broad‐scale land‐use and habitat‐related drivers of upland wader population declines, providing pointers to their respective roles in driving these declines.

Correlates of the change in Ring Ouzel Turdus torquatus abundance in Scotland from 1988–91 to 1999

CapsuleThe change was correlated with environmental, habitat and management variables. Aims To identify factors correlated with a population decline and range contraction between 1988–91 and 1999. Methods Regression models are used to describe the variation in Ring Ouzel abundance in 1988–91, and the change in Ring Ouzel abundance between 1988–91 and 1999. Results The abundance of Ring Ouzels in 1988–91 was negatively correlated with improved pasture, but positively with heather/smooth grass mosaic and Nardus/Molinia grassland. There was also a positive quadratic correlation with rock cover. A decline in Ring Ouzels between 1988–91 and 1999 was most likely on tetrads with shallow gradients, and outside of a 350–750 m altitudinal range. The change in ouzel numbers was also negatively correlated with both the initial area of conifer forest and heather/smooth grass mosaic. The rate of loss was greatest in those areas with a low Ring Ouzel abundance in 1988–91, although this effect was non-significant once habitat was accounted for. Conclusions The abundance of Ring Ouzels was linked to heather–grass mosaics, while declines were greater in tetrads lacking topographical features known to be selected by nesting ouzels. The negative relationship between forestry and population change suggests that large-scale afforestation of the uplands is a cause of concern.

Long-term trends in the abundance of breeding Lapwing Vanellus vanellus in relation to land-use change on upland farmland in southern Scotland

Capsule A long-term decline on this habitat is shown to be associated with the intensification of agricultural management, particularly the occurrence of field drainage. Aims To assess long-term trends in the number of breeding Lapwing and determine the relationship between these trends and changes in agricultural management on an upland study area. Methods Breeding Lapwing were counted along two road transects in nine years between 1980 and 2002, and on one extensive plot in 1980, 1990 and 2000. Counts along the road transects were made from a vehicle and the fields used for nesting were recorded. Changes in field management along the transects were monitored annually between 1980 and 1990, and habitat composition assessed in 1980, 1985, 1990 and 2000. Results During the first 20 years of study the number of breeding Lapwing declined substantially on all three count areas and by 77% overall, with further declines on both transects in 2002. The area of unimproved grassland and arable on these transects also declined substantially due to conversion to improved grass. Fields that comprised either unimproved grassland or arable were most likely to hold nesting Lapwing, while the chance of a field losing its nesting Lapwing was positively associated with the occurrence of drainage. Drainage and conversion to improved grass were closely linked. Conclusions Agricultural intensification is a probable cause of decline in the number of breeding Lapwing in upland areas. Such declines may have been widespread in upland areas following increased agricultural intensification in recent decades.

Observer variation in estimates of Meadow Pipit Anthus pratensis and Skylark Alauda arvensis abundance on moorland

Capsule Counts least susceptible to observer effects were those within 25 m of a transect and the total number along a transect, with observer effects greater for distance sampling.

Estimating the abundance and hatching success of breeding Curlew Numenius arquata using survey data

Counts of individual Curlew and estimates of breeding pairs from ‘field-by-field’ surveys were highly correlated with the numbers of nesting pairs, as determined by intensive studies on 27 sites located on four grassland-dominated study areas. The mean count of individual Curlew over three standard survey visits to each site was used to estimate numbers of nesting pairs. This estimate exceeded the number of nesting pairs on all study areas (as assessed by intensive studies) by 12% but was more accurate than the maximum number of pairs estimated from the three survey visits on each site (the previous convention for estimating breeding pairs). Estimates of the number of pairs hatching chicks were assessed by recording alarm-calling Curlew during late survey visits. The maximum number of alarm-calling pairs was used to estimate the number of pairs hatching chicks, overestimating this by 54%. Three of the study sites were adjacent to extensive moorland which produced overestimates during surveys because moorland nesting birds fed and led broods onto these sites. Omitting these sites from consideration reduced the degree of overestimation to 1% for the number of pairs and 7% for the number of pairs hatching chicks.

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.

POSTFLEDGING SURVIVAL, MOVEMENTS, AND DISPERSAL OF RING OUZELS (TURDUS TORQUATUS)

ABSTRACT. Recent evidence suggests that avian population growth rates may be constrained by low postfledging survival. Therefore, quantifying postfledging mortality and understanding the ecological factors that influence it are fundamental for assessing the relative importance of this life-history stage for population growth and identifying the ecological drivers of population dynamics. We radiotracked 110 juvenile Ring Ouzels (Turdus torquatus), a species of high conservation concern in the United Kingdom, to test hypotheses regarding the timing and causes of postfledging mortality and to quantify the timing and magnitude of local movements and dispersal. Juveniles fledged from early-season broods had higher survival during each 4-day period over 116 days postfledging (0.952 ± 0.011 [SE]) than juveniles fledged from late-season broods (0.837 ± 0.021). Most mortality occurred within the first 3 weeks postfledging, and predation by raptors and mammals was the main apparent cause of mortality, accounting for 59% and 27% of deaths, respectively. Juvenile survival decreased at the age of independence from parental care. Juveniles traveled increasing distances from their nests with time after fledging, and those that fledged early in the season dispersed outside the study area at significantly older ages than those that fledged late in the season.

How might CAP reform influence land management, moorland vegetation, birds, economy and employment?

Common Agricultural Policy (CAP) reform will impact significantly on the management of upland areas and associated wildlife and socio-economic interests. This paper draws on work within a field and modelling study that models a wide range of management scenarios for four contrasting field sites. To pilot this approach, one of the grazing field sites (ADAS Redesdale in Northumberland) was used as a starting template with five scenarios. This paper summarises the approach, which integrates theoretical models with field studies, to investigate management changes.