Abstract
Bird migration is typically associated with a latitudinal movement from north to south and vice versa. However, many bird species migrate seasonally with an upslope or downslope movement in a process termed altitudinal migration. Globally, 830 of the 6,579 Passeriformes species are considered altitudinal migrants and this pattern has emerged multiple times across 77 families of this order. Recent work has indicated an association between altitudinal migration and diet, but none have looked at diet as a potential evolutionary driver. Here, we investigated potential evolutionary drivers of altitudinal migration in passerines around the world by using phylogenetic comparative methods. We tested for evolutionary associations between altitudinal migration and foraging guild and primary habitat preference in passerines species worldwide. Our results indicate that foraging guild is evolutionarily associated with altitudinal migration, but this relationship varies across zoogeographical regions. In the Nearctic, herbivorous and omnivorous species are associated with altitudinal migration, while only omnivorous species are associated with altitudinal migration in the Palearctic. Habitat was not strongly linked to the evolution of altitudinal migration. While our results point to diet as a potentially important driver of altitudinal migration, the evolution of this behavior is complex and certainly driven by multiple factors. Altitudinal migration varies in its use (for breeding or molting), within a species, population, and even at the individual level. As such, the evolution of altitudinal migration is likely driven by an ensemble of factors, but this study provides a beginning framework for understanding the evolution of this complex behavior.
Highlights
Altitudinal migration is generally described as a seasonal movement from lower elevations to higher elevations for the breeding season and a downslope movement for the nonbreeding season (Barçante, Vale, & Alves, 2017; Hayes, 1995; Mackas et al, 2010)
We explored two potential drivers of the evolution of altitudinal migration in passerines by conducting large-scale phylogenetic comparative analyses
Our results indicate that foraging guild is evolutionarily associated with altitudinal migration, but this relationship varies across zoogeographic regions
Summary
Altitudinal migration is generally described as a seasonal movement from lower elevations to higher elevations for the breeding season and a downslope movement for the nonbreeding season (Barçante, Vale, & Alves, 2017; Hayes, 1995; Mackas et al, 2010). Some studies on altitudinal migration have provided evidence that frugivorous bird abundance is linked to fruit and flower abundance (Chaves-Campos, 2004; Kimura et al, 2001; Levey, 1988; Loiselle & Blake, 1991) while others have shown no evidence of this phenomenon (Boyle, 2010; Hart et al, 2011; Papeş, Peterson, & Powell, 2012; Rosselli, 1994). Frugivory has been suggested as a driver of altitudinal migration, in part because frugivorous altitudinal migrants have been observed more frequently at higher elevations in Costa Rica (Blake & Loiselle, 2000; Boyle, Conway, & Bronstein, 2011) and Nepal (Katuwal et al, 2016). We expected that frugivorous and nectivorous species were driven toward altitudinal migration in the Neotropics because they were tracking fruit and flower abundance which varies seasonally (Barçante et al, 2017; Chaves-Campo, 2004; Kimura et al, 2001; Levey, 1988; Loiselle & Blake, 1991). We expected altitudinal migration to be evolutionary associated with forest habitats in the Neotropics because altitudinal migrants in Costa Rica (Stiles, 1988; Stiles & Clarke, 1989) and southeastern Brazil (Stotz, unpublished—see Stotz, Fitzpatrick, Parker, & Moskovits, 1996), for instance, include a high number of restricted-range and forest-dependent species
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