Why Come Back Home? Investigating The Proximate Factors That Influence Natal Philopatry In Migratory Passerines

Knowledge of which cues attract birds back to natal areas is important for conservation because the cues could be manipulated to attract breeders to source habitat or discourage breeders from settling in sink habitat. We examined the influence of intrinsic and extrinsic variables on natal philopatry using two metrics, short-distance natal dispersal and the probability of philopatry to the natal field, in two obligate-grassland bird species breeding in an agricultural landscape: the bobolink, Dolichonyx oryzivorus, and the Savannah sparrow, Passerculus sandwichensis. During 2002–2014, we detected 90 locally hatched Savannah sparrows and 129 locally hatched bobolinks breeding as adults near their places of origin (mean ± SD dispersal distances: Savannah sparrows: 917 ± 851 m; bobolinks: 1251 ± 839 m). For both species, the location of the field on which they bred relative to fields where annual productivity was greater than replacement best explained variation in natal dispersal distance. The probability a Savannah sparrow was philopatric to its natal field increased if it fledged later in the season, while this probability decreased if there was an opposite-sex parent or sibling present on the natal field, or the field was under a late-hay management scheme. None of the variables considered explained variation in bobolink natal philopatry. Natal philopatry and short-distance natal dispersal in these species appear to be influenced by factors that are difficult to manage; however, land managers should attempt to keep management consistent across time to reduce misinformation in dispersal cues