TROPICAL PHENOLOGY IN TEMPERATE REGIONS: EXTENDED BREEDING SEASON IN A LONG-DISTANCE MIGRANT

摘要

The chronology of birds' breeding has traditionally been thought to depend strongly on latitude, although it can be rather uneven among populations in close proximity. I estimated the extent of the breeding season in a population of the Red-necked Nightjar (Caprimulgus ruficollis) over three years in southwestern Spain. Data from brood patch development and appearance of recently fledged young provided evidence for a breeding season unusually extended (110 days) for a long-distance migrant. Flexible timing in reproduction appeared to affect individual's departure in migration. Although most adult nightjars gradually left the study area beginning in mid August, some late breeders left the area about a month later than the earliest migrants. Decreasing competition for food and free nesting territories, together with a food supply and predation pressure constant through the season, resemble conditions in the tropics and enable the nightjars to breed over an extended period despite inhabiting a temperate region. The nightjars' phenology was further expanded by a protracted period (≥35 days) of parental care, which also led to later molt prior to autumn migration. However, birds partially compensated for time costs to adjust to the annual cycle by initiating a simultaneous shedding of flight feathers immediately after hatching. In accordance with current studies showing how breeding events carry over into the annual routines of birds, results from this nightjar population come on top of recent hypotheses regarding new ways in which breeding, molt and migration could interact and condition each other.