Monday, February 4, 2013

Cats Kill Billions of Birds and Small Mammals Each Year? Maybe Not

Barbara J. King notes on that there is a backlash to all the cat-killer headlines last week after a study was published in the journal Nature Communications.

King states there are serious reasons to suspect the reliability of the new study and notes:

“The study at issue is a meta-analysis, an overarching review that aggregates data from previously published sources… for a meta-analysis to be solid, wise choices must be made among the available sources of information, and results that may vary wildly must be weighed fairly.”

She highlights areas of concern, which include:
  • The study authors needed to incorporate into their model the number of un-owned cats in the U.S., and they note in an appendix to the article, "no empirically driven estimate of un-owned cat abundance exists for the contiguous U.S.” 
  • The study authors also note local that analyses of cat numbers are "often conducted in areas with above average density," and of eight sources of information used, "three [were] based on nationwide pet-owner surveys and five based on research in individual study areas." 

King questions whether these local studies are representative of the national situation and whether the different owner surveys were administered in a manner consistent enough to allow them to be aggregated.

She goes on to say:

“Of course, the authors make statistical perturbations designed to increase the reliability of their conclusions, but it seems to me there's an unsettling degree of uncertainty in the study's key numbers.”

And she quotes Wayne Pacelle of the Humane Society of the United States as saying:

"It's virtually impossible to determine how many cats live outside, or how many spend some portion of the day outside. Loss, Will, and Marra [the study authors] have thrown out a provocative number for cat predation totals, and their piece has been published in a highly credible publication, but they admit the study has many deficiencies. We don't quarrel with the conclusion that the impact is big, but the numbers are informed guesswork."

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