Résumé
1. To successfully perform their long-distance migrations, migratory birds
require sites along their migratory routes to rest and refuel. Monitoring
the use of so-called stopover and staging sites provides insights into (1)
the timing of migration and (2) the importance of a site for migratory
bird populations. A recently developed Bayesian superpopulation model that
integrates mark-recapture data and ring density data enabled the
estimation of stopover timing, duration and population size. Yet, this
model did not account for heterogeneity in encounter (p) and staying (ϕ)
probabilities. 2. Here we extended the integrated superpopulation model by
implementing finite mixtures to account for heterogeneity in p and ϕ. We
used simulations and real data on red knots Calidris canutus staging in
Bohai Bay, China, during spring migration to (1) show the importance of
accounting for heterogeneity in encounter and staying probabilities to get
unbiased estimates of stopover timing, duration and numbers of migratory
birds at staging sites and (2) get accurate stopover parameter estimates
for a migratory bird species at a key staging site that is threatened by
habitat destruction. 3. Our simulations confirmed that heterogeneity in p
affected stopover parameter estimates more than heterogeneity in ϕ. Bias
was particularly severe when most birds had both low ϕ and p. Bias was
largest for population size, intermediate for stopover duration and
negligible for stopover timing. 4. 50,000-100,000 red knots were estimated
to annually stop for 5-9 days in Bohai Bay between 10 and 30 May. This
shows the key importance of this staging site for this declining species.
There were no clear changes in stopover parameters over time. 5. Our study
shows the importance of accounting for heterogeneity in both encounter and
staying probabilities for accurately estimating stopover duration and
population size and provides an appropriate modelling framework.