Wednesday, July 8, 2015

Coyotes ensure cat-free refuges for birds


In old cartoons, coyotes and roadrunners are arch-enemies. But in present-day ecosystems, a coyote may be a bird’s best friend, carving out areas of habitat where birds can sing in safety because pussy cats fear to tread.

That’s the upshot of research published June 24 in the Journal of Mammalogy, from the first large-scale study of the roaming habits of domestic cats in the United States. Scientists have raised concern about the ecological impact of house cats, estimating that the nation’s more than 74 million pet cats kill billions of birds and small mammals each year. On oceanic islands, cats have caused extinction of 18 small vertebrate species and are the primary threat to 36 more. But few hard data are available on how cats affect population levels of mainland species.

The new study suggests that domestic cats don’t hunt much in protected areas, and likely pose relatively little risk to populations of sensitive native birds that depend on these habitats – at least, provided that other predators, like coyotes, are also present. Instead, the impact of cats on bird populations is probably concentrated in urban areas.

To reach this conclusion, researchers from North Carolina State University recruited nearly 500 citizen scientists, undergraduate students, and middle schoolers to deploy and monitor motion-sensing research cameras, or “camera traps,” placed in 32 protected areas across six eastern U.S. states, as well as backyards and small urban forests in Raleigh, North Carolina – a total of 2,117 sites in all.

The researchers analyzed the patterns in 52,863 pictures of wildlife that resulted from this effort. The most important predictor of cat presence was coyote density, they found: where coyotes are, cats aren’t.

Coyotes were common in protected areas, found in all but one of the 32 protected areas studied, and detected 33 times more frequently than cats in this habitat. Cats, on the other hand, were completely absent from half of the protected areas. A single cat was photographed in each of 14 protected areas, while just two protected areas harbored multiple cats.

Instead, cats mostly stick to residential yards, where they were detected 300 times more often than they were protected areas. And here coyotes were rare: only five of the backyards in the study yielded snapshots of coyotes.

Studies of cats and coyotes will need to be conducted in other cities, the researchers say, especially those where coyotes may be more urbanized. But the broad geographic scale of the protected areas included in the study suggests that the results reflect general ecological patterns, rather than just relationships that are specific to a particular location.

And overall, the researchers conclude, the presence of coyotes tends to exclude cats from protected areas. More evidence for this view comes from Gambrill State Park in Maryland, the only protected area that lacked coyotes, which also had the highest level of cat activity.

To be sure, the study results don’t entirely negate concerns about the ecological impact of outdoor cats. But they do suggest that this impact is likely to be most acute in – quite literally – cats’ own backyards.

More broadly, the study shows that the new, human-mediated species assemblages that now characterize many parts of the planet can involve surprising interrelationships. Coyotes are relatively recent arrivals to the eastern United States, and human activities like the extirpation of wolves and reforestation of prior agricultural lands are thought to have contributed to their range expansion from the west. They’re often seen as unwelcome migrants – in no small part because they prey on pets like cats — yet it turns out they may also benefit species that have a longer evolutionary history in their new home. Coyote, in other words, remains a trickster.   

– Sarah DeWeerdt | 7 July 2015

Source: Kays R. et al. 2015 Cats are rare where coyotes roam. Journal of Mammalogy DOI: 10.1093/jmammal/gyv100
Header image:  A coyote noses around a woodpile near a house in Capels Mill, North Carolina. Credit: John Flannery via Flickr.

source: Conservation Magazine