Jacquie A. Clark

Recruitment and survival of immature seabirds in relation to oil spills and climate variability

1. In long-lived animals with delayed maturity, the non-breeding component of the population may play an important role in buffering the effects of stochastic mortality. Populations of colonial seabirds often consist of more than 50% non-breeders, yet because they spend much of their early life at sea, we understand little about their impact on the demographic process. 2. Using multistate capture-mark-recapture techniques, we analyse a long-term data set of individually identifiable common guillemots, Uria aalge Pont., to assess factors influencing their immature survival and two-stage recruitment process. 3. Analysis of the distribution of ringed common guillemots during the non-breeding season, separated by age classes, revealed that all age classes were potentially at risk from four major oil spills. However, the youngest age class (0-3 years) were far more widely spread than birds 4-6 years old, which were more widely spread than birds aged 6 and over. Therefore the chance of encountering an oil spill was age-dependent. 4. A 2-year compound survival estimate for juvenile guillemots was weakly negatively correlated with winter sea-surface temperature, but was not influenced by oil spills. Non-breeder survival did not vary significantly over time. 5. In years following four oil spills, juvenile recruitment was almost double the value in non-oil-spill years. Recent work from Skomer Island showed a doubling of adult mortality associated with major oil spills, which probably reduced competition at the breeding colony, allowing increased immature recruitment to compensate for these losses. We discuss the implications of compensatory recruitment for assessing the impact of oil pollution incidents.

Changes in commercially fished shellfish stocks and shorebird populations in the Wash, England

Abstract The Wash, in eastern England, supports internationally important populations of 11 species of shorebird. A major commercial shellfishery provides potential conflict between fishermen and nature conservation interests. During the 1990s, high fishing mortality and low recruitment substantially reduced the stocks of cockle (Cerastoderma edule) and mussel (Mytilus edulis). Population models, constructed from estimates of survival and recruitment, indicated that declines in the availability of cockles and mussels were associated with changes in oystercatcher (Haemotopus ostralegus) survival between 1970 and 1998, including three periods of mass mortality, and also the recruitment of juvenile birds to both oystercatcher and knot (Calidris canutus) populations. Emigration of knot may also have taken place. Cockle recruitment was dependent on climatic conditions, whereas mussel populations tended to be stable. The decline in mussel stocks, due to over-fishing, increased the vulnerability of the oystercatcher population to mass-mortality episodes in poor cockle years. The key to preventing major oystercatcher kills in future is to ensure sufficient mussels are available in poor cockle years. Recent cultivation of mussels in inter-tidal areas has been beneficial and is an important management tool for maintaining bird populations.

Effects of Horseshoe Crab Harvest in Delaware Bay on Red Knots: Are Harvest Restrictions Working?

Each May, red knots (Calidris canutus rufa) congregate in Delaware Bay during their northward migration to feed on horseshoe crab eggs (Limulus polyphemus) and refuel for breeding in the Arctic. During the 1990s, the Delaware Bay harvest of horseshoe crabs for bait increased 10-fold, leading to a more than 90% decline in the availability of their eggs for knots. The proportion of knots achieving weights of more than 180 grams by 26–28 May, their main departure period, dropped from 0.6–0.8 to 0.14–0.4 over 1997–2007. During the same period, the red knot population stopping in Delaware Bay declined by more than 75%, in part because the annual survival rate of adult knots wintering in Tierra del Fuego declined. Despite restrictions, the 2007 horseshoe crab harvest was still greater than the 1990 harvest, and no recovery of knots was detectable. We propose an adaptive management strategy with recovery goals and annual monitoring that, if adopted, will both allow red knot and horseshoe crab populations to recover and permit a sustainable harvest of horseshoe crabs.

Mass-dependent predation risk as a mechanism for house sparrow declines?

House sparrow (Passer domesticus) numbers have declined rapidly in both rural and urban habitats across Western Europe over the last 30 years, leading to their inclusion on the UK conservation red list. The decline in farmland has been linked to a reduction in winter survival caused by reduced food supply. This reduction in food supply is associated with agricultural intensification that has led to the loss of seed-rich winter stubble and access to spilt grain. However, urban house sparrows have also declined, suggesting that reduced food supply in farmland is not the sole reason for the decline. Here, we show that changes in house sparrow mass and thus fat reserves are not regulated to minimize starvation risk, as would be expected if limited winter food were the only cause of population decline. Instead, the species appears to be responding to mass-dependent predation risk, with starvation risk and predation risk traded-off such that house sparrows may be particularly vulnerable to environmental change that reduces the predictability of the food supply.

The EURING exchange code 2000

The EURING code, which has been the European standard coding system for observations on marked birds, has undergone a major revision and extension resulting in the EURING EXCHANGE CODE 2000. Major aspects of change have a background in computer-technology, a shift in scientific questions and in the interaction between the two. Over the last decades, studies aimed at measuring survival rates and dispersal of individuals have become major questions for bird ringing besides migration research. In these studies one has many observations on the same individual. Therefore, the old code, where each record had a ringing and a finding (dead or alive) part, has been replaced and now each record describes one encounter with the bird. This also facilitates coding all the ringing data, before any subsequent observations have been made. New fields and changed coding make it possible to record many more details about methods used and greater precision of coordinates. The new code specifically allows for recording repeated observations of the same individual arising from other marking systems, such as e.g. radio- or satellite tracking or transponders. The code is freely available and it is hoped that many people will use it, since the future opportunities of using data from different sources that have been coded in the same way are enormous.

How climate change might influence the starvation-predation risk trade-off response

Climate change within the UK will affect winter starvation risk because higher temperatures reduce energy budgets and are likely to increase the quality of the foraging environment. Mass regulation in birds is a consequence of the starvation–predation risk trade-off: decreasing starvation risk because of climate change should decrease mass, but this will be countered by the effects of predation risk, because high predation risk has a negative effect on mass when foraging conditions are poor and a positive effect on mass when foraging conditions are good. We tested whether mass regulation in great tits (Parus major) across the UK was related to temporal changes in starvation risk (winter temperature 1995–2005) and spatial changes in predation risk (sparrowhawk Accipiter nisus abundance). As predicted, great tits carried less mass during later, warmer, winters, demonstrating that starvation risk overall has decreased. Also, the effects of predation risk interacted with the effects of temperature (as an index of foraging conditions), so that in colder winters higher sparrowhawk abundance led to lower mass, whereas in warmer, later, winters higher sparrowhawk abundance led to higher mass. Mass regulation in a small bird species may therefore provide an index of how environmental change is affecting the foraging environment.

Declining rates of ring recovery in British birds

A major focus of national ringing schemes is the large‐scale analysis of survival rates, primarily from recoveries of birds found dead. We demonstrate, based on analyses of birds ringed in Britain and Ireland between 1960 and 1998, a pronounced and consistent decline in the numbers of ringed birds found dead and reported across a wide range of species with diverse ecologies. The extent of these declines can, in some cases, be explained by factors pertinent to particular species, but most appear to stem from changes in reporting behaviour. Continued declines in recovery rate will reduce the precision with which we can estimate survival rates, but use of new web‐based technologies may help reverse this decline.

Bird ringing in Britain and Ireland in 1996

This is the 60th annual report of the British Trust for Ornithologys Ringing Scheme, presenting the data received in 1996. The development and implementation of a Scientific Strategy for the Ringing Scheme is discussed, together with examples of future work and data analysis. The strategy provides a coherent approach to the collection of data needed for future analytical work on bird populations within Britain and Ireland, ensuring that questions of conservation importance are addressed. The number of birds ringed during the current period (851,237) was slightly down on that for 1995, but remained some 2.8% up on the mean for the previous five years. For several species there were changes in the number of individuals ringed (when compared with previous years) which could not be explained by changes in ringing effort. These included increases for Firecrest, Fieldfare and Barn Owl and a decrease for Crossbill. The total number of recoveries for the period (12,342) is nearly 5% down on the mean for the prev...

Bird ringing in Britain and Ireland in 2003

This is the 67th annual report of the British Trust for Ornithologys Ringing Scheme, covering work carried out, and data received, in 2003. During the year, reports of ringed birds were used to assess the post‐release survival of rehabilitated individuals. Varying proportions of different species were able to re‐enter the population, with Mute Swan Cygnus olor being the most successful. The origins and age structure of Guillemots Uria aalge ringed in Britain & Ireland and found dead after five major oil spills in European waters were found to vary depending on the location of the oil spill. More immature birds and birds from eastern colonies tended to be found after spills that were further south, whereas spills in the north had a greater effect on adults and birds from western colonies. Work on mass gain strategies in Blackbirds Turdus merula showed that they put on mass in winter, when the threat of starvation is greatest, as well as changing mass through the day, again probably in response to the likelihood of starvation. A study of the survival of passerines in the few weeks after fledging found that the survival rate during this critical period is only aboutone sixth of the rate in the rest of the first year of life. A study of the demography of Spotted Flycatcher Muscicapa striata showed that changes in post fleding survival were the most likely mechanism for the observed population decline. Data gathered as part of the Constant Effort Sites (CES) Scheme showed that adult abundance among resident species was generally high, following a good breeding season in 2002. When compared to 2002, fledgling productivity in 2003 was lower, probably as a resultof cold, wetweather during the breeding season. A total of 111 Retrapping Adults for Survival (RAS) studies submitted data covering 43 species. Target species for future workwere identified. Continuing work on the winter movements of farmland passerines showed variations in the distances moved by different species. Over 11,000 Swallows Hirundo rustica were ringed aspartofthe Swallow Roost Project. The total number of birds ringed (848,532) increased for the second year and was 5% above the mean of the previous five years (1998–2002). The recovery total (11,554) was also 5% up on the five‐year mean (1998–2002). Recoveries of 180 BTO‐ringed birds and 76 ringed abroad are presented in the report; those included confirm known or suspected movement patterns or are unexpected movements.

Sex differences in the migration, moult and wintering areas of British‐ringed Ruff

Male Ruff Philomachus pugnax are considerably larger than females. Of the 351 birds caught by the Wash Wader Ringing Group, 68% of the adults were males while only 34% of the juveniles were males. Analysis of ringing recoveries of British ringed birds showed that females tended to migrate to Africa while males tended to winter in Europe. The moult patterns of male and female adult Ruff on the Wash differ significantly with males starting moult earlier and having more feathers in moult at one time. The possibility that this is related to migration patterns is discussed.