Carl Mitchell

Effects of climate change on European ducks: what do we know and what do we need to know?

The consequences of climate change for bird populations have received much attention in recent decades, especially amongst cavity-nesting songbirds, yet little has been written on ducks (Anatidae) despite these being major elements of wetland diversity and important quarry species. This paper reviews the major known consequences of climate change for birds in general, and relates these to the limited information available specifically for ducks. Climate change can influence migration distance and phenology, potentially affecting patterns of mortality, as well as distribution and reproductive success in ducks. Studies addressing effects of climate change are, however, restricted to very few duck species, including mallard Anas platyrhynchos and common eider Somateria mollissima. Shifts in winter duck distributions have been observed, whereas the mismatch hypothesis (mistiming between the periods of peak energy requirements for young and the peak of seasonal food availability) has received limited support with regard to ducks. We propose a range of monitoring initiatives, including population surveys, breeding success monitoring schemes and individual duck marking, which should later be integrated through population modelling and adaptive management to fill these gaps.

Winter movements and site-fidelity of Pink-footed Geese Anser brachyrhynchus ringed in Britain, with particular emphasis on those marked in Lancashire

Census data show that the distribution of Pink footed Geese Anser brachyrhynchus in different parts of their winter range in Britain changes within seasons. Large numbers arrive during October and November in Grampian Region, east-central Scotland, Borders Region, Lothian Region and Lancashire. Numbers peak in England during mid-winter, with few persisting into March, by which time the more sedentary winter populations of south-west Scotland and throughout eastern Scotland have begun to be augmented, presumably through arrivals from further south. Maximum numbers occur in northern Grampian and the Moray Firth from March onwards and peak during April. Individually marked Pink footed Geese captured in Lancashire dispersed to the Ribble Estuary, the south Lancashire Mosses and elsewhere in north-west England. Part of this population moves on to spend mid-winter in Norfolk. In January, there is a conspicuous migration northwards in Britain, with individuals travelling through Fylde, the Solway and east-centra...

Movements and migrations of Wigeon Anas penelope wintering in Britain and Ireland

The paper describes an analysis of 1419 recoveries of Wigeon ringed in Britain and Ireland and 401 recoveries in that area of foreign-ringed birds. They result from ringing carried out from the ear...

Measures of annual breeding success amongst Eurasian Wigeon Anas penelope

Capsule Inferences are drawn on the basis of first-winter young: adult ratios. Aim To obtain the most error- and bias-free index of annual reproductive success for the species based on existing data. Methods We compared age and sex ratios amongst shot birds in Denmark and the UK with those amongst samples of birds caught for ringing purposes and field observations in the UK. Results The annual proportions of young amongst the four samples were highly correlated. The ratio of adult males to adult females showed no significant difference between any of the measures, but was lowest amongst field observations. The ratio of first-winter males to first-winter females was even in the ringing and shot samples, suggesting differential survival of the sexes after the first winter affects the global sex ratio. In the ringed sample, the proportion of first-winter birds was similar from November to March, suggesting winter migrants to the UK contained a similar proportion of adults to first-winter birds. Over the same period, the proportion of first-winter birds determined by field observations increased, suggesting the timing of body moult in winter males may overestimate numbers of females in autumn flocks. Annual variation in productivity from samples of duck wings collected in Denmark and the UK were correlated, and, on average, were 9% higher in Denmark. There was a significant long-term decline in the proportion of young recorded in the UK. Conclusion There was support for the prediction that selective hunting affects age (but apparently not sex) ratios of Wigeon in winter. It was concluded that hunting bags and ringing samples could provide useful indices of annual production of young over extended periods and that production of young was correlated with temperatures on the breeding grounds.

Connectivity between flyway populations of waterbirds: assessment of rates of exchange, their causes and consequences

Summary 1. Conservation and management of migratory waterbirds use flyway populations as the basic unit, and knowledge of the delineation, rate of exchange and gene flow between populations is fundamental. However, for the majority of global flyway populations, information is too fragmentary to address connectivity between populations and, hence, insufficient to inform management. 2. We investigated the demographic connectivity between the eastern (breeding in Svalbard and wintering in Denmark, the Netherlands and Belgium) and western (breeding in Greenland or Iceland and wintering in Britain) flyway populations of pink-footed geese Anser brachyrhynchus based on resightings of marked geese from both populations. Previous genetic analyses suggested a modest gene flow between the two populations. 3. Capture–recapture analysis conservatively estimated that mean annual movement probabilities were low (eastern to western population: 0071%, 95% CI = 0033–015%; western to eastern: 0076%, 95% CI = 0031–018%). Movement probability from eastern to western flyway populations increased in years with high snow cover in the southernmost winter range in Belgium. Life histories of exchanged individuals from eastern to western (32 different individuals during 1988–2010) revealed that the majority entered Britain via Belgium and the Netherlands during winter; some returned to the eastern population via Belgium and/or the Netherlands, others moved northwards in Britain during the spring and appear to have migrated directly from Britain (western population) to Norway (eastern population). None of the birds from the eastern population emigrated permanently, but some individuals turned up in Britain in consecutive years. Out of nine individuals switching from western to eastern flyway populations, three returned to Britain; the others were not subsequently resighted. An alternative winter strategy and spring flyway over Britain to Norway is suggested, used by hundreds to thousands of eastern birds, particularly following severe winters. Thus, the two populations currently appear to be demographically closed; low genetic connectivity probably reflects dispersal over longer time. 4. Synthesis and applications. Current initiatives to internationally manage the eastern population of pink-footed geese do not need to consider net immigration in predictive harvest models. For waterbirds in general, a targeted approach to evaluate connectivity, using classic marking studies in combination with molecular methods and focussed sampling on breeding grounds, is recommended to better underpin management decisions at population levels.

Rafting behaviour and predator disturbance to Steller's EidersPolysticta stelleri in northern Norway

Stellers Eiders responded to overflying Great Black-backed GullsLarus marinus by “spooking” — flushing from feeding and aggregating on open water. Birds did not react at high tide when aggregated into dense roosting flocks. The significant reduction in inter-bird distance associated with this escape behaviour suggests that rafting in this way (and at rest) serves an anti-predator function. In 32% of spooks, up to 56% of the flocks were displaced from feeding sites; even when all birds remained, they took an average of 3.5 minutes for half of the flock to resume feeding, representing a minimum total of 17% loss of feeding time throughout the 24 hour period. At observed rates, the cost of flight behaviour in response to gulls was estimated to equate to a minimum of 7.8% of daily existence energy. Hence such predator responses can cost Stellers Eiders loss of access to favoured feeding area, loss of feeding time (already restricted by tidal exposure) and additional energy costs. Auf überfliegende Mantelmöwen reagieren Scheckenten, in dem sie überstürzt von ihren Nahrungsplätzen auffliegen und sich auf dem offenen Wasser zusammenscharen. Wenn sich die Enten bei Flut zu dichten Ruhegesellschaften zusammengeschlossen haben, ist keine Reaktion zu beobachten. Die Reduktion der Individualabstände in Verbindung mit Fluchtverhalten deutet darauf hin, daß der enge Zusammenschluß eine Reaktion gegen Räuber bedeutet. In 32% der Fluchtbewegungen entfernten sich bis zu 56% der Trupps von den Stellen der Nahrungssuche. Aber auch, wenn die Vögel am Ort bleiben, dauerte es im Mittel 3,5 min, bis die Hälfte der Trupps die Nahrungssuche wieder aufgenommen hatte. Dabei gingen innerhalb von 24 Stunden immerhin 17% der Zeit für Nahrungssuche verloren. Die Kosten für das überstürzte Abfliegen beim Auftauchen von Möwen wird auf etwa 7,8% des täglichen Mindestenergiebedarfs geschätzt. Daher kann eine derartige Raktion auf potentielle Räuber die Nutzung bevorzugter Nahrungsgründe einschränken sowie Verlust der ohnehin durch die Gezeiten beschränkte Zeit für Nahrungsaufnahme und zusätzliche Energiekosten nach sich ziehen.

Distribution and status of wintering Shovelers Anas clypeata in Great Britain

The distribution and status of Shovelers using British wetlands in autumn and winter was examined using ringing recoveries and National Waterfowl Count data. Maximum counts have been around 8500 and suggest a total population of c. 10 000. Some of these birds originate from north-west continental Europe, eastern Scandinavia and the Western former USSR, whilst others originate from British breeding populations. Numbers peaked in October, after which there was a steady emigration from Britain as birds moved to France, the Iberian Peninsula and Mediterranean for the winter. The population fell sharply during the early 1960s and then increased up until 1971/72. Since then there has been a gradual, though slight, decline. The number counted decreased nationally during periods of cold weather, suggesting cold weather emigrations. Wintering Shovelers have increased their usage of reservoirs and mineral workings, and slightly decreased their usage of natural lakes. Patterns of seasonal occurrence varied between r...

Within-winter movements and site fidelity of Icelandic Greylag Geese Anser anser

Capsule Levels of mobility and turnover changed at different stages of the non-breeding season. Aims To describe the pattern of within-winter movements of Icelandic Greylag Geese in northern Britain and to assess the rate of turnover at different stages of the non-breeding season. Methods Sightings of marked individuals were used to describe movements throughout the wintering range, while more detailed local studies were used to assess rates of turnover. Results Greylag Geese were most mobile and turnover greatest during the early winter period (October–December). Birds were least mobile and turnover lowest during the midwinter period. In spring (March–April) rates of turnover slightly increased as did movement between areas. Despite this it seemed that most birds probably made a direct flight to Iceland from their final wintering area without staging in north Scotland. Conclusions Greylag Geese were highly mobile, particularly on arrival from their Icelandic breeding grounds. They were less mobile in midwinter and spring. There was little evidence of a northerly return movement within Britain in spring. Most departed to Iceland directly from their final wintering locations. Evidence of an expansion in the known range is also presented.

Use of GPS tags to describe the home ranges, migration routes, stop-over locations and breeding area of Taiga Bean Geese Anser fabalis fabalis wintering in central Scotland

ABSTRACT Capsule: Taiga Bean Geese Anser fabalis fabalis wintering near Falkirk, Scotland staged in Denmark, Norway and Sweden and summered in central Sweden. Aims: To determine the migration routes, timing of movements, breeding area and home ranges of Taiga Bean Geese wintering near Falkirk, Scotland. Methods: Ten Taiga Bean Geese, caught on the wintering grounds in Scotland, were marked with neck collars carrying global positioning system (GPS) tags. A further 21 geese were fitted with individually marked plastic neck collars. GPS location data were collected and field counts and searches for individually marked geese were undertaken to provide detailed information on their location throughout the year. Results: Seven GPS tags provided information away from Scotland, indicating that two migration routes were used en route to the breeding grounds in Dalarna, Sweden. During the non-breeding season, the total home range of the geese was approximately 466 km2, although the total area within agricultural fields used by the geese may have been as small as 13 km2. Conclusions: The timing of movements, migration routes, breeding area and identification of important stop-over sites for this wintering population are described for the first time.

The status and distribution of summering Greylag Geese Anser anser in Scotland, 2008–09

Capsule Summering Greylag Geese Anser anser are increasing in number and expanding their range in Scotland. Aims During the summers of 2008 and 2009, extensive surveys of Greylag Geese in Scotland were undertaken to update the current distribution and population estimates, as well as estimate breeding success. Methods Checks of known moult-sites were combined with a random stratified sample of lochs to the south and east of the Great Glen (the ‘re-established population’ area). Sample lochs were selected on the basis of altitude, the proportional areas of woodland and water cover and previous summer records of Greylag Geese within the 10-km squares in which the lochs were located. To the north and west of the Great Glen (the ‘northwest Scotland’ population area), comprehensive post-breeding counts of feeding areas were undertaken in late August. Results Combined results from 2008 and 2009 suggest an estimated 47 405 (range 44 059–51 763) Greylag Geese in Scotland. Since 1989, Greylag Geese encountered to the south and east of the Great Glen (derived from re-established birds) have increased at an annual rate of about 9.7% per annum and, since 1997, those in northwest Scotland have increased at an annual rate of about 11.7% per annum. It is estimated that the total number of Greylag Geese summering in Britain is about 84 500 birds. In 2008, overall breeding success was 24.1% young in the late summer population, which probably more than compensates for natural and shooting mortality. Conclusion There is no indication of a decline in the rate of increase of Greylag Geese in Scotland and the species is expected to continue to increase in abundance and distribution.