The quantitative study of marked individuals in ecology, evolution ...

EURING 2003 Radolfzell
growing population has been performed over the last 20 years throughout the country
by many volunteers. Using this large-scale and long-term ringing and resighting data
set, we constructed capture-recapture models to investigate the variation of lifehistory
traits underlying the dynamics of this population, and the consequences of the
reintroduction program on these traits.
In a first step, we fully describe the effects of age, time, cohort and trap-dependence
on White stork survival and resighting rates, thus providing precise estimates of these
traits. A gradual increase in both survival and resighting rates with age is described
for the first time in this long-lived species. Interestingly, survival rate decreases with
time, paralleling the increase in the proportion of free-flying individuals in the population.
These results also allow us to account for time and age effects in investigating
the consequences of supplementary feeding on life-history traits, while keeping capture-recapture
models tractable in these further analyses.
The exact causes of the White Stork population decline were not clear, but mortality
on migration is thought to have increased (exacerbated by the proliferation of highvoltage
power lines across Europe). Adverse weather on the wintering grounds could
also have depressed survival. Supplementary feeding may then have ameliorated
survival either by giving the birds a better body condition prior to migration, or by encouraging
them to stay behind, surviving the European winter on artificial food supplements.
In a second step, we thus used detailed data on the location of breeding
attempts with respect to the food sources over the country (food was provided at the
breeding stations) to assess the consequences of supplementary feeding on survival,
resighting rate and migratory behaviour. More specifically, we investigate whether
survival rate to the next year, resighting rate and migrating probability depend on food
availability during the breeding season. Food availability was considered to decrease
with increasing distance from the nest to the nearest breeding station. Further, we
analyse potential differences in survival rate according to individual migratory status
(i.e. migratory vs. resident individuals). This status is defined using resighting data
collected all over Europe and Africa. Preliminary analyses suggest that survival does
not differ according to food availability, but the probability of migrating decreases with
increasing food availability.
Overall, our results emphasize the importance of the large scale population monitoring
in obtaining life-history trait estimates that will prove useful for managers to make
efficient decisions for future strategies of conservation for the White stork in the
Netherlands. Building an integrated demographic population model with the precise
estimates obtained via our analyses, based on data collected at large spatial scales,
will indeed eventually allow reliable predictions on the long-term population dynamics
to be made under different conservation scenarios.
02:20 PM - 02:45 PM
Estimating correlates of survival rates from nationally coordinated ringing data on
owls in Finland
Pertti Saurola & Charles Francis
Since 1974, bird ringers in Finland have been encouraged to ring both nestlings and
adults of many species of birds of prey, especially owls. This coordinated effort, involving
several hundred ringers, now results in more than 30,000 potential nest sites for
owls being checked annually, and has led to over 200,000 owls being ringed in Finland
up until 2002. Many of these owls are subsequently recaptured as breeding
adults, by the same or different ringers, while others are recovered dead by the general
public. All of the ringing and encounter data, as well as many biometric data are
centrally computerized, allowing for large-scale analyses of geographic and temporal
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