Innes M.W. Sim

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.

Status of the Hen Harrier Circus cyaneus in the UK and Isle of Man in 2004, and a comparison with the 1988/89 and 1998 surveys

Capsule The population of breeding Hen Harriers in the UK and Isle of Man increased between 1998 and 2004, although country and regional trends differed. Aims To estimate the size of the UK and Isle of Man Hen Harrier breeding population in 2004, and to compare this with previous estimates made in 1988/89 and 1998. Methods Surveys were carried out in core and a stratified random sample of 10-km squares throughout the known range, using the same methods as in the 1988/89 and 1998 national surveys. Results There were an estimated 806 territorial pairs in the UK and Isle of Man in 2004, a significant 41% increase from the 1998 estimate of 570 pairs. Increases were found throughout, with the exception of south and east Scotland and England, where numbers decreased. Scotland held 79% of the UK and Isle of Man breeding population in 2004, and 10% of Scottish pairs were associated with non-moorland habitats, such as mature conifer plantations and scrub/brash. Conclusions There was a substantial increase in the breeding population in most regions of the UK and Isle of Man between 1998 and 2004, possibly aided by increased use of non-moorland habitats. However, populations declined in upland areas of southern and eastern Scotland and northern England. Continuing illegal persecution arising from perceived conflicts between breeding Hen Harriers and driven grouse shooting may be a major cause of these regional declines.

Abundance of male Black Grouse Tetrao tetrix in Britain in 2005, and change since 1995-96

Capsule There was a non-significant decline in the number of displaying males in Britain between 1995–96 and 2005, with a significant decline in Scotland. Aims To estimate the number of displaying male Black Grouse in Britain in 2005, and to compare this with the 1995–96 estimate. Methods Surveys were carried out in a stratified sample of 1-km (Wales) and 5-km (Scotland and England) squares throughout the known range, using similar methods to the 1995–96 survey. Results There were an estimated 5078 displaying males in Britain in 2005 (95% CI 3920–6156). This estimate is 22% less than the 1995–96 estimate of 6506, although these estimates are not significantly different. In Scotland, numbers fell by 29% overall, comprising large and significant declines of 49% and 69% in southwest and southeast Scotland, respectively, but small and non-significant declines in north (16%) and northeast Scotland (9%). In England, there was a non-significant decline of 11%, while in Wales numbers rose by 39%. Where numbers have declined there has been a decrease in the number, but not the size, of display groups. Display sites in Britain were at higher altitudes (median 400 m) in 2005 than in 1995–96 (median 340 m). Conclusion Although Black Grouse numbers in Wales increased, this survey provides evidence of a large decline in southern Scotland. The causes of this decline are not fully understood, and further research is urgently required to reveal the underlying mechanisms and implement appropriate conservation measures.

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.

The status of the Hen Harrier, Circus cyaneus, in the UK and Isle of Man in 2010

Capsule The fourth national survey of Hen Harrier showed that the population in the UK and the Isle of Man declined significantly between 2004 and 2010. Aim To estimate the size of the breeding Hen Harrier population (with associated 95% confidence intervals) in the UK and Isle of Man, constituent countries and Scottish regions, in 2010 and calculate population change since previous surveys in 1998 and 2004. Methods Complete surveys were made of 10-km squares likely to be occupied by breeding Hen Harriers in England, Wales, Northern Ireland and the Isle of Man, using standard methods developed for previous national surveys. In Scotland, a ‘census’ area was non-randomly selected for survey by volunteers, and randomly selected squares were surveyed in two strata covering the rest of the known range. Results The UK and Isle of Man Hen Harrier population was estimated at 662 territorial pairs (95% confidence interval (CI): 576–770), a significant decline of 18% since 2004. Scotland holds the bulk (76%) of the population (505 territorial pairs; 95% CI: 417–612), with smaller numbers in Northern Ireland (59 pairs), Wales (57 pairs), the Isle of Man (29 pairs) and England (12 pairs). Declines of 49% and 20% were observed in the Isle of Man and in Scotland, respectively, whereas the Welsh population increased by 33%. A significant decrease was recorded in numbers of pairs using young and mature plantation forest in Scotland. Conclusion The breeding population of Hen Harriers in the UK and Isle of Man declined between 2004 and 2010. Notable decreases in Scotland and the Isle of Man may be related to habitat change and illegal persecution. Illegal persecution continues to limit the population size of harriers in England to very low levels.

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.

Catching methods and biometrics of breeding Ring Ouzels Turdus torquatus torquatus in northeast Scotland

Between 1999 and 2002, we caught 116 (54 male and 62 female) breeding adult Ring Ouzels Turdus torquatus torquatus in Glen Clunie, northeast Scotland. Four different catching methods are described and their success assessed. There was no evidence that any catching method had a detrimental effect on either nest outcome, or the frequency of second breeding attempts in the same year. Plumage characteristics were used to age and sex birds caught, following their use to age and sex migrants and museum specimens. These characteristics were found to be reliable for all 19 birds of known age. Males had, on average, longer wings and deeper and whiter gorgets than females, but they were not heavier. Among both males and females 2+ year birds had, on average, longer wings than 2nd year birds, and 2+ year females were also heavier and had whiter gorgets than 2nd year birds.

Frequency of multiple brooding in Ring Ouzels, including first documented cases of triple brooding

Capsule The majority of female Ring Ouzels made two successful breeding attempts in a single season, but triple brooding was much less common.

Changes in moorland and heathland bird abundance in southwest England in relation to environmental change

ABSTRACT Capsule: Population changes of many moorland and heathland birds in southwest England show associations with environmental change, and the area supports notable breeding populations of species of conservation concern. Aims: To quantify changes in moorland and heathland breeding bird abundance in relation to changes in environmental variables. Methods: A two-visit moorland bird survey method was used to estimate the abundance of 23 target bird species in 2008 and 2014 in Exmoor National Park, southwest England. Data on changes in 25 environmental variables over the same period were used to test associations between changes in bird abundance and environmental change. Results: Fourteen species increased in abundance and nine decreased. Breeding species which wintered on or close to Exmoor were less likely to show negative population changes than species which migrated to winter in southern Europe or Africa. Change in abundance of 18 species was associated with change in at least one environmental variable, and these relationships were broadly consistent with the known ecology of these species. Conclusion: Although some moorland species have declined or gone locally extinct, this area of moorland and heathland in southwest England remains an important stronghold for several species of high conservation concern. The maintenance of semi-natural moorland and heathland habitats in areas such as Exmoor may provide important refuges for such species, both now and in the future.