Abstract
Many species of birds and bats undertake seasonal migrations between breeding and over-wintering sites. En-route, migrants alternate periods of flight with time spent at stopover – the time and space where individuals rest and refuel for subsequent flights. We assessed the spatial scale of movements made by migrants during stopover by using an array of automated telemetry receivers with multiple antennae to track the daily location of individuals over a geographic area ∼20×40 km. We tracked the movements of 322 individuals of seven migratory vertebrate species (5 passerines, 1 owl and 1 bat) during spring and fall migratory stopover on and adjacent to a large lake peninsula. Our results show that many individuals leaving their capture site relocate within the same landscape at some point during stopover, moving as much as 30 km distant from their site of initial capture. We show that many apparent nocturnal departures from stopover sites are not a resumption of migration in the strictest sense, but are instead relocations that represent continued stopover at a broader spatial scale.
Highlights
Billions of birds and bats undertake seasonal, nocturnal migrations between over-wintering and breeding grounds
Our results reveal that during a stopover bout, migrants from multiple taxa with diverse migration strategies frequently undertake flights from monitored stopover sites that do not result in a continuation of migration, but rather are movements between stopover sites within a broader stopover landscape
Similar results have been observed for shorebirds where individuals regularly undertake ‘within-stopover’ movements [8,28] but the behaviour is not usually reported for passerines and even more rarely for owls and bats. The implication of this result is that to properly quantify migratory behaviour at stopover, researchers need to ensure that they are surveying at spatial scales that fully represent the stopover landscape
Summary
Billions of birds and bats undertake seasonal, nocturnal migrations between over-wintering and breeding grounds. Periods of flight alternate with time spent at ‘stopover’ – the time and space where individuals rest and refuel for a subsequent migratory flight. A ‘stopover bout’ can be thought of as the time spent between migratory flights [5]. The site where an individual is found at any particular time during a stopover bout can be thought of as its ‘stopover site’. A stopover landscape can be spatially and temporally equal to or larger than a stopover site [6] The difficulty with these definitions is in determining whether an individual has undertaken a true migratory flight as opposed to a flight that only involves changing stopover sites within the stopover landscape
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