What’s the News: After tracking baby gray catbirds with miniature radio transmitters, biologists found that cats were by far the #1 bird killer: 47 percent of the birds died at the paws of pet and feral felines (out of 80 percent that were killed by predators in general). This echoes some biologists’ view that cats are a destructive, human-assisted invasive species: “Cats are way up there in terms of threats to birds — they are a formidable force in driving out native species,” said one of the authors of the study.
What’s the Context:
Not So Fast: While cats were the biggest threat to birds in this study, the lead author notes that the biggest culprit for bird deaths over all is still building collisions.
Reference: Balogh, Anne L., Ryder, Thomas B., and Marra, Peter P. 2011. Population demography of Gray Catbirds in the suburban matrix: sources, sinks and domestic cats. Journal of Ornithology. DOI 10.1007/s10336-011-0648-7 (pdf)
Image: flickr / emilydickinsonridesabmx
Up in the sky, under the sea, deep inside an animal society—researchers can’t go these places themselves, so they attach tracking devices to wildlife in order to gather the data. But are these gizmos invisible to the creatures themselves, and can they go about their lives the same way they would if they didn’t have a tracker stuck on their fin or wing? Or do some of these electronic devices interfere with the animals’ ways of life, and therefore send back bad data to the scientists?
This week there’s a new entry into this long-running debate, regarding one of the most-tracked animals in the world: the king penguin of Antarctica. A study published in Nature that tracked 100 penguins found that those wearing flipper bands lived different lives than those without, and less successful ones to boot.
In terms of survival, banded penguins had a 16 44 percent lower rate [survival rate dropped from .36 to .20, a drop of 16 percentage points, or 44 percent] over the entire 10 years, but there is a breakpoint at 4.5 years. In the first 4.5 years, banded penguins actually had a 30 percent higher mortality rate. After that, the difference in mortality between banded and unbanded birds levels off. The authors propose that flipper-banding acts as an artificial selector for the strongest penguins, creating a bias in data collected from banded birds. Over the decade, banded birds were less successful in breeding. Banded penguins produced a total of 47 chicks, while unbanded penguins had 80 chicks. [Ars Technica]
This study presents a practical problem: Studying the effects of clipped-on tracking tags means your control group must be free of them, but you have to track the group without the flipper bands somehow. So Yvon Le Maho’s team implanted small, newer-style tags that lie under the skin on all the penguins in their study. That way they could give half of the birds a dummy tracking tag clipped on the fin to see if the equipment itself changes their behavior.