Influence of spatial scale, sex and parental presence on rates of natal philopatry in non-migratory Canada Geese Branta canadensis
Birds often nest in the same area where they were raised (natal philopatry). The level of natal philopatry among non-migratory Canada Geese Branta canadensis in New Haven County, Connecticut, USA, was studied by banding 731 fledglings, then following them over their lives. The proportion of fledglings that returned to New Haven County to nest as adults (i.e. natal return rates) was 0.22 overall: 0.31 for females and 0.12 for males. These rates increased to 0.60 for females and 0.29 for males after correcting for mortality prior to first breeding (i.e. natal homing rates). For 29 fledglings (2 males and 27 females) that hatched in the Maltby Lakes and returned as adults to breed in New Haven County, I knew the location of their natal site, first nesting site, final nesting site, and the identity of their parents and mate. These 29 birds are referred to as “subjects”. During their first nesting year, 28 of 29 subjects (96%) raised their young at their natal brood-rearing site: 17 (59%) nested on their natal lake, 6 (21%) nested on their natal area (often an island within the lake), and 2 (7%) on their natal territory. These percentages were higher than expected if geese were selecting nest sites at random for brood-rearing sites and natal lakes, but not for natal areas or natal territories. Natal philopatry rates were similar during the subjects’ first and last nesting year, and there was also no difference between subjects raised in crèche broods and those raised in two-parent families. Natal philopatry could be mistaken for parental philopatry (i.e. offspring nesting close to their parents). To test this, the location of nesting territories was examined for those subjects that had parents nesting concurrently on a new nesting territory rather than at the subject’s natal territory. Results showed that both natal and parental philopatry occurred; distances to the natal territory and parents’ current territory were similar. Geese that exhibit natal philopatry will complicate efforts to manage geese at large scales, such as states or flyways.
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