Short‐distance partial migration of Neotropical birds: a community‐level test of the foraging limitation hypothesis

Abstract

Partial migration of tropical birds was long believed to be driven by variation in food abundance. Recent evidence from a partially‐migratory species suggests that in contrast, limited foraging opportunities at high elevations during severe wet season storms drives the most metabolically‐challenged individuals down to elevations where rainfall is lighter. Here, I test community‐level predictions of this hypothesis by examining the relationship between high‐elevation rainfall in the second half of the year and counts of migrant birds in lowland forest during late December each year from 1990–2009. I contrast results derived from analysis of all migrant species with both analyses of only the frugivorous migrants, and analyses of resident species. Counts of migrant species were on average positively associated with montane rainfall with differences of up to 72% in the numbers of birds counted in drier or wetter years. Frugivores and smaller birds responded more strongly to variation in rainfall compared to the broader migrant species pool. Interestingly, counts of resident species were also higher following wetter montane wet seasons. Results of analyses exploring the cause of resident responses were not consistent with climatic effects on breeding productivity or short‐term weather effects on detectability. Results were, however, consistent with cryptic down‐slope migration of individuals breeding at higher elevations augmenting lowland resident populations in wet years. These results suggest that changes in rainfall amount, storm intensity, and timing of severe weather events would lead to large increases in or losses of an important behaviour.

Partial migration in fishes: definitions, methodologies and taxonomic distribution

“…In a growing number of examples, individuals from the same population show differences in migratory behaviour, with some migrating on seasonal or diel time scales between habitats whilst others remain resident in a single habitat (Dingle, 1996). This within‐population migratory dimorphism is known as partial migration and is ubiquitous amongst migratory taxa, with many examples of partially migratory invertebrates, fishes, birds and mammals documented in the wild (Hansson & Hylander, 2009; Boyle, 2011; Cagnacci et al, 2011; Grayson et al, 2011).…”

Seasonal changes in partial, reverse diel vertical migrations of cisco Coregonus artedi

“…interspecific competition for limited food resources causes partial DVM) (Gauthreaux, ), and the fasting endurance hypothesis ( i.e . organisms at greater risk of starvation are more likely to migrate) (Jahn et al ., ; Boyle, ). The predation vulnerability hypothesis was partially supported by Mehner & Kasprzak () for Coregonus spp.…”

Range expansion and noteworthy records of Costa Rican birds (Aves)

“…These species probably are undergoing elevational movements as has been reported for altitudinal migrants in the Neotropics that descend to lowland forest during the dry season (Loiselle andBlake 1991, Boyle 2010). However, the presence of these species in lowlands may be due to poor weather conditions in the highlands, which may cause individuals to move to the lowlands in search of food or to avoid the adverse weather (Avalos 2005, Boyle 2010, 2011.…”