Loss of breeding grounds hits a sad note for common songbird

Date:  November 29, 2017

Source:  Tulane University

A Tulane University researcher who studies bird migration has found that a decline in the number of wood thrushes is probably due to deforestation in Central America, not to the loss and degrading of forest in the United States where the songbird breeds.

The study by Caz Taylor, an associate professor in the Tulane Department of Ecology and Evolutionary Biology, was published Nov. 6 in the open-access journal Scientific Reports.

Wood thrushes breed in the forests of the eastern United States and migrate in the winter to the forests of Central America. Although they remain a relatively common bird, the species has been declining rapidly since the early 1970's and several researchers have suggested that fragmentation of forests in breeding grounds are playing a major role.

In the new study, Taylor examines how breeding forest fragmentation relates to the shape and strength of density-dependence or how dwindling resources limit bird population. She was surprised to find that declines were more severe in regions where the forest was the least fragmented.

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Secret nocturnal lives of wood thrushes

Date:October 21, 2015

Source:Central Ornithology Publication Office

We know surprisingly little about what songbirds do after the sun goes down, but past studies have provided tantalizing hints that many forest birds roost for the night in different habitat from where they spend the day. For a study forthcoming in The Auk: Ornithological Advances, Vitek Jirinec of the College of William and Mary and his colleagues captured and radio-tagged Wood Thrushes (Hylocichla mustelina) to track their movements during both day and night. Their results, the first broad description of roosting ecology for a migratory North American songbird during breeding season, show that the birds often move out of their daytime ranges to sleep, seeking dense areas of vegetation where they're safe from predators.

Jirinec and his colleagues tracked 47 birds on the coastal plain of southeastern Virginia during the breeding seasons of 2013 and 2014, including 37 males and 10 of their mates. They found that males were not faithful to particular roosting spots, regularly moving from night to night, and overall one third of the roosting locations were completely outside the birds' daytime ranges. Remote sensing data showed that those nighttime roosts were located in areas with higher-than-average canopy density, and the researchers suggest that the birds could have been making these commutes in order to roost in safer sleeping spots, where they would be well-hidden from predators.

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