Correlates and consequences of breeding dispersal in a migratory songbird

Abstract

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Breeding Dispersal by Birds in a Dynamic Urban Ecosystem

“…From 2002–2010 we obtained 504 consecutive locations on 337 adults (hereafter ‘movements,’192 in changing, 67 in reserve, and 78 in developed sites). We measured the distance between successive year’s territory centroids (the nest site, when known, or the central point with greatest activity observed during spot mapping, when nest was not located; as in [34] in m, using a portable GPS in the field or after assessing locations of activity on high resolution satellite imagery and field maps generated by geographic information systems at the end of the field season. We define breeding site fidelity for each species as movements less than the species-specific average maximum radius of territories we measured in each study landscape.…”

“…Averaging enables each individual bird to be included in these broad analyses regardless of our knowledge of individual histories. However, when relating movement to annual productivity, fidelity to mate, and land cover in the territory, we followed [34] and considered an individual’s annual movement to be the experimental unit because each movement was associated with a unique history (preceded by a unique reproductive event that was often conducted with a different partner in a territory that was in a unique location surrounded by different neighbors and where human action frequently changed the local vegetation). We used standard parametric or exact tests to investigate the relationship between variables other than dispersal distance.…”

“…Breeding dispersal—the annual shift in an adults’ center of reproductive activity [33]—remains one of the least understood yet fundamental processes by which animal populations adapt to their environment [34]. Breeding dispersal reflects not only an individual’s decision to remain faithful to a site, but also often its decision to remain faithful to a mate.…”

“…Breeding dispersal in birds is generally of shorter distance than natal dispersal, often more extensive by females than males, and motivated by differential costs of movement and benefits of retaining one’s mate or territory [33, 35]. Costs and benefits are affected by a rich mix of individual and environmental characteristics, including population density, territory quality, pair compatibility, success and quality of neighbors, actions of predators and parasites, and an individual’s sex, social status, age, and previous experience [34, 36–38]. In urban environments breeding dispersal is rarely studied [39] and may be influenced by the above factors as well as the actions of humans that benefit or challenge birds [40].…”

“…First, we expect reproductive failures to stimulate breeding dispersal (Table 1, 2A) and reduce mate fidelity (Table 1, 2E) [43, 44]. Additionally, we expect breeding dispersal distance to increase (Table 1, 2B, 2C and 2F) and mate fidelity to decrease where habitats of varying quality exist near one-another because birds with poor quality territories will move to attain high quality territories (Table 1, 2D and 2E) [34, 45, 46]. Finally, the third question motivates a test of the hypothesis that following failure, increased number or quality of young are produced by individuals that disperse farthest or abandon mates to pursue better options, however this presumed benefit is inconsistently realized (Table 1, 3A–3F) [38, 47].…”