Abstract
Nearctic-neotropic migrant birds need to replenish energy reserves during stopover periods to successfully complete their semiannual movements. In this study we used linear models to examine the habitat use of 11 migrant species in northeastern Costa Rica to better understand the influence of food and structural resources on the presence of birds during stopover periods. Our models indicated that frugivorous migrants primarily used food abundance, while insectivorous migrants chiefly used vegetation structure as cues for habitat use during stopover. In addition to habitat use models, we documented fruiting plant phenology and found a general relationship between migrant arrival and the timing of ripe fruit availability. Our results suggest that insectivorous migrants probably rely on structural features when using habitat because it may be inherently difficult to assess cryptic-arthropod availability during a short period of time in a novel habitat, such as stopover periods.
Highlights
Mortalities accrued during migratory periods may regulate population growth of some bird species [1,2,3]
In addition to conservation, examining relationships between stopover areas and habitat use can identify the behavioral adaptations migrants employ, such as diet switching from insects to fruit, to successfully use a diversity of habitats throughout temperate and tropical latitudes [9,10,11]
Cues pertaining to initial stopover habitat selection and subsequent use are not necessarily exclusive and may depend heavily on predator avoidance and food resource availability
Summary
Mortalities accrued during migratory periods may regulate population growth of some bird species [1,2,3]. Sillett and Holmes [2] estimated that 85% of apparent mortality occurred during migratory periods for populations of Blackthroated Blue Warblers (Setophaga caerulescens) captured in New Hampshire, USA, and Jamaica. During their migratory periods, Nearctic-neotropic migrants (hereafter referred to as ‘migrants’) rely on stopover habitats that provide reliable food resources where birds can replenish their energy reserves necessary to successfully complete their semi-annual movements [4,5]. Cues pertaining to initial stopover habitat selection and subsequent use are not necessarily exclusive and may depend heavily on predator avoidance and (or) food resource availability. To explore the influence of food and vegetative structure on migrant habitat use we simultaneously collected bird capture, food resource and structure data during fall migration in northeastern Costa Rica to test the following predictions: (1) If habitat use is influenced by migrant diet and spatial variation in resource supply, high capture rates will correspond with sites rich in fruit and (or) insects; (2) If habitat use is influenced by selection for specific structural features (e.g., tree height, foliage density), high capture rates will correspond with sites with specific, preferred vegetative characteristics
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