There comes a time in life for every bird to spread its wings and leave the nest, but for gray catbirds, that might be the beginning of the end. Smithsonian scientists report fledgling catbirds in suburban habitats are at their most vulnerable stage of life, with almost 80 percent killed by predators before they reach adulthood. Almost half of the deaths were linked to domestic cats.
Urban areas cover more than 100 million acres within the continental the United States and are spreading, with an increase of 48 percent from 1982 to 2003. Although urbanization affects wildlife, ecologists know relatively little about its effect on the productivity and survival of breeding birds. To learn more, a team of scientists at the Smithsonian's Migratory Bird Center studied the gray catbird (Dumatella carolinensis) in three suburban Maryland areas outside of Washington, D.C.Bethesda, Opal Daniels and Spring Park.
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 percent of juvenile catbird deaths within the team's three suburban study sites. Nearly half (47 percent) of the deaths were attributed to domestic cats in Opal Daniels and Spring Park. The deaths were either witnessed by the scientists or determined to be cat-related by the condition of the fledgling's remains, such as a decapitated bird with the body left uneatendefining characters of a cat kill. Domestic cats were never detected during predator surveys in the third suburban study site, Bethesda.
"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 decid
|Contact: John Gibbons|