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Impact of cats on young birds in the suburbs

Posted on 19. April, 2011.

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A new study on the effects of urbanisation on wildlife that tracked the early lives of grey catbirds in three Washington, D.C. suburbs found that outdoor cats were the number one source of known predation on the young birds.

The study by Drs Peter Marra and Thomas Ryder of The Smithsonian Institution and Anne L. Balogh of Towson University was published online in the January 2011 edition of the Journal of Ornithology.

The team found that factors such as brood size, sex or hatching date played no significant role in a fledgling’s survival. The main determining factor was predation, which accounted for 79% of juvenile catbird deaths within the team’s three suburban study sites. Nearly half (47%) of the deaths were attributed to domestic cats.

“The predation by cats on fledgling catbirds made these suburban areas ecological traps for nesting birds,” said Peter Marra, Smithsonian research scientist. “The habitats looked suitable for breeding birds with lots of shrubs for nesting and areas for feeding, but the presence of cats, a relatively recent phenomenon, isn’t a cue birds use when deciding where to nest.”

Technology made tracking the fledgling catbirds possible. The team fitted 69 fledglings with small radio-transmitters. Scientists tracked each individual and recorded its location every other day until they died or left the study area. This detailed type of field research was very limited until recently when transmitters were made small and light enough for songbirds.

Tracking the fledglings revealed that the vast majority of young catbird deaths occurred in the first week after a bird fledged from the nest. This was not surprising to the team, given that fledglings beg loudly for food and are not yet alert to predators—making fledglings in suburban environments particularly prone to visual predators such as domestic cats. Domestic cats in suburban areas that are allowed outside spend the majority of time in their own or adjacent yards, so they are likely able to intensely monitor, locate and hunt inexperienced juvenile birds. Rats and crows were also found to be significant suburban threats to fledgling catbirds.

 “Cats are natural predators of not just birds but also mammals,” said Marra. “Removing both pet and feral cats from outdoor environments is a simple solution to a major problem impacting our native wildlife.”

The full article can be in J. Ornithol. doi: 10.1007/s10336-011-0648-7Online First™.

In Picture: Catbird and young. Photo courtesy of Leupold, James, US Fish and Wildlife Service.

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