Determinants of nest box local recruitment and natal dispersal in a declining bird population

Recruitment and dispersal are important demographic rates and studying
their determinants is particularly important in the current context of
global anthropogenic perturbations. In birds, and especially for migratory
species, assessing these rates is challenging because of the difficulties
involved in tracking individuals beyond fledging. Here we assessed the
determinants of nest box local recruitment and natal dispersal distances
in a declining aerial insectivore, the Tree swallow (Tachycineta bicolor).
We used a 16-year dataset obtained from the long-term monitoring of a
population breeding within a 10,200-km2 study system located along a
gradient of agricultural intensification in southern Québec, Canada.
Yearly nest box local recruitment rates ranged there in between 1.0% and
3.2%. Heavier nestlings who fledged earlier were more likely to recruit.
Natal dispersal distances were generally short (mean ± SD = 12.7 ± 13.8
km) in the study system and were influenced by different factors depending
on sex. Females dispersed over shorter distances when conspecific
occupancy on breeding site was high, while males dispersed farther in the
presence of competing House sparrows (Passer domesticus) and when their
mother was young. Selection of breeding locations appeared to take place
at multiple scales and individuals recruited in sites with characteristics
similar to their natal sites. Our results provide important information
concerning the factors influencing nest box local recruitment and natal
dispersal dynamics of this migratory species. These factors should be
considered in conservation practices for this species in order to support
production of recruits in habitats favorable to their survival.