Comparing the seasonal survival of resident and migratory oystercatchers: carry‐over effects of habitat quality and weather conditions (original) (raw)
Related papers
2009
Animals facing partial habitat loss can try to survive in the remaining habitat or emigrate. Effects on survival and movements should be studied simultaneously since survival rates may be underestimated if emigrants are not considered, and since emigrants may experience reduced survival. 2. We analysed movements and survival of adult wintering oystercatcher Haematopus ostralegus in response to the 1986-1987 partial closure of the Oosterschelde in the Dutch Delta. This reduced by one-third the tidal area of this major European wintering area for waders. 3. We developed a novel variant of a multistate capture-recapture model allowing simultaneous estimation of survival and movement between sites using a mixture of data (live recaptures and dead recoveries). We used a two-step process, first estimating movements between sites followed by site-specific survival rates. 4. Most birds were faithful to their ringing site. Winter survival was negatively affected by winter severity and was lowest among birds changing wintering site (i.e. moving outside of the Oosterschelde). 5. During mild winters, survival rates were very high, and similar to before the closure in both changed and unchanged sectors of the Oosterschelde. However, the combined effect of habitat loss with severe winters decreased the survival of birds from changed sectors and induced emigration. 6. The coastal engineering project coincided with three severe winters and high food stock, making assessment of its effects difficult. However, the habitat loss seems to have had less impact on adult survival and movements than did winter severity. 7. Synthesis and applications . Human-induced habitat change may result in population decline through costly emigration or reduced survival or reproduction of individuals that stay. Long-term monitoring of marked individuals helps to understand how populations respond to environmental change, but site-specific survival and movement rates should be integrated in the same model in order to maximize the information yield. Our modelling approach facilitates this because it allows the inclusion of recoveries from outside the study area.
Ibis, 2008
Population models show that the response of migratory bird populations to a reduction in the area, or change in the quality, of their winter feeding areas depends critically on the shape (linear or non-linear) and strength (slope) of the relationship describing how the proportion dying from starvation changes with population density. Yet the parameters that define such density-dependent functions are extremely difficult to estimate from direct measurements of mortality at different population sizes. Even if they could be estimated, there would be uncertainty as to whether or not the relationship would remain the same, and thus provide reliable predictions, in the new circumstances for which forecasts are required. This paper summarizes studies of the Oystercatcher Haematopus ostralegus which aim to derive the shape and strength of the winter density-dependent mortality and emigration function for one estuary, under existing and new circumstances, from the responses of individual birds to each other and to their spatially and seasonally varying food supply. Based on these studies, an individuals-based, physiologicalIy structured game theoretic distribution model has been built which predicts the carrying capacity and numbers of birds dying at different population sizes. The model also can be applied to Oystercatchers occupying several estuaries distributed throughout their wintering range and can thus be extended to the entire biogeographical or global population. In addition, it can be used to identify some easily measured behavioural and ecological parameters that identify those species, from a wide range of taxa, that are most likely to be affected by habitat loss and change. Many activities on estuaries may threaten the specialized shorebirds Charadrii that largely rely on intertidal areas when
Population size of Oystercatchers Haematopus ostralegus wintering in Iceland
Bird Study, 2018
Capsule Iceland-breeding Oystercatchers winter in both Iceland and W Europe, but the relative numbers of residents and migrants is poorly known. We undertook the first ever survey of the total number of Oystercatchers wintering in Iceland. Around 11,000 individuals were counted which almost triples the previous estimate. This is an estimated 30% of the Icelandic population, including juveniles, suggesting that ~26,000 Icelandic Oystercatchers migrate to W Europe in the autumn. More Oystercatchers winter in Iceland than at similar latitudes elsewhere in Europe, which may reflect the remoteness and slightly milder winter temperatures on this oceanic island.
The Journal of Applied Ecology, 1995
1. This paper models empirically how habitat loss in winter might affect the size of the European population of oystercatchers Haematopus ostralegus ostralegus. It explores how a density-dependent mortality rate in winter interacts with a density-dependent production rate in summer to determine the total, year-round population size following a loss of winter habitat which itself leads to intensified competition for food and hence increased winter mortality rates. 2. Simulations over a range of probable parameter values show that the density at which winter mortality becomes density-dependent, cW, simply determines the point at which population size is affected as habitat is gradually removed. The population is affected sooner in the more widely fluctuating Continental subpopulations than in the less variable Atlantic subpopulations. 3. Once winter density reaches cW, the consequences depend on the slope, bW, of the density-dependent winter mortality function. In all subpopulations, the reduction in population size increases sharply as bW increases, but only at low values; above a certain level, further increases in bW make less difference. Because of their higher reproductive rate, inland subpopulations are initially less affected by winter habitat loss than coastal subpopulations. These conclusions are robust over a range of assumptions about competition for territories in summer and age difference in mortality in winter. 4. Adding density-dependent fledging success to the basic model reduces the effect of winter habitat loss on population size, but only when low proportions of the habitat are removed. A higher mortality rate in females, whether only in postfledging young birds or in birds of all ages, makes little additional difference to the population consequences of habitat loss. 5. Field studies on winter habitat loss in migratory bird populations should first test whether density has already reached the critical level, cW; i.e. whether some birds already die of food competition. The parameter bW should then be estimated to determine whether its probable value lies in the range within which predictions are sensitive or insensitive to its precise value. Whether the summer density-dependent functions are linear or curvilinear needs also to be explored, as does the effect of interactions between subpopulations which have different fledgling production rates but share the same winter habitat.
Growth, fledging success and post-fledging survival of juvenile Oystercatchers Haematopus ostralegus
Ibis, 2008
We studied the consequences of differences in growth rate on the subsequent survival of Oystercatcher Haernatopus ostralegus chicks. Fledging success increased sharply with growth rate, from zero in chicks growing at less than 6 g per day to about 85% in chicks growing at more than 10 g per day. The age at which chicks fledged varied from 27 to 52 days. Chicks which fledged at an early age displayed a much faster growth rate than later fledging chicks. Although slow growth resulted in a considerable prolongation of the period before fledging, slow-growing chicks fledged at a smaller size and with a lower bodyweight than fast-growing chicks. After fledging, all chicks remained almost completely dependent on their parents up to an age of 3 months and often longer. Almost 40% of the fledglings eventually returned to the breeding area. This figure probably reflects post-fledging survival. Age and size at fledging had no effect on a chick's probability of return. Bodyweight at fledging had a small positive correlation with the return probability, but this was not statistically significant. We conclude that although slow growth severely reduces a chick's chance of fledging, it probably does not result in irreversible damage causing an increased risk of mortality during the first years after fledging. Apparently, any possible disadvantage associated with small size or low bodyweight could be compensated for after fledging.
Waterbirds, 2012
Using mark-recapture models, apparent survival was estimated from older banding and re-sighting data (1978-1983) of American Oystercatchers (Haematopus palliatus) nesting on beaches and in salt marshes of coastal Virginia, USA. Oystercatchers nesting in salt marshes exhibited higher apparent survival (0.94 ± 0.03) than birds nesting on beaches (0.81 ± 0.06), a difference due to variation in mortality, permanent emigration, or both. Nesting on exposed barrier beaches may subject adults and young to higher risk of predation. These early estimates of adult survival for a species that is heavily monitored along the Atlantic and Gulf Coasts can be used to (1) develop demographic models to determine population stability, (2) compare with estimates of adult survival from populations that have reached carrying capacity, and (3) compare with estimates of survival from other oystercatcher populations and species.
Waterbirds, 2017
Information on demographic parameters needed to inform conservation strategies for American Oystercatchers (Haematopus palliatus) is lacking. The population dynamics of American Oystercatchers in Virginia, USA, were examined using a multi-state analysis framework that modeled movement of American Oystercatchers into and out of the State. Change in breeding status, age-specific survival rates, and age at first breeding were investigated for three geographically distinct study sites. Non-breeding American Oystercatchers originating from Virginia readily moved in and out of the State among years. The immigration rate for birds breeding on barrier islands was 6%. Emigration rates were 6% for the barrier island breeding population and 17% for the seaside lagoon population. Stage-specific annual survival rates were 0.66, 0.95 and 0.91 for juvenile, sub-adult and adult stages, respectively. Age at first breeding peaked in the fourth year for both the barrier island and seaside lagoon breeding populations. Movement and recruitment rates suggested that the barrier islands may provide the highest quality breeding habitat among the three study sites. This study showed that Virginia's American Oystercatcher population is linked with other Atlantic Coast populations, and these links should be considered when evaluating local population trends and management targets.