Chicago is one of the largest cities in north America with a human population of over 8 million. The study took place from 2008 to 2010 at various locations in the northwestern suburbs, including public parks, conservation areas, and a private wildlife reserve. The research team were already collecting data on coyotes in this area, making it the perfect location for a study of how cats manage to co-exist with coyotes.
Free-roaming cats, rather than pet cats, were the focus. Traps, baited with canned cat food, were set up at the study locations and checked at least once, usually twice, a day. One of the sites was close to a cat colony, where a local Trap Neuter and Return group kept an eye on the cats. Any cats that appeared to be owned – for example, because they were in excellent condition, or wearing a collar – were released and excluded from the study.
Cats that were considered ‘feral’ were sedated, weighed, measured, and blood samples were taken to test for four infectious diseases: feline leukaemia (FeLV), FIV, feline heartworm, and toxoplasma gondii. Then they were fitted with radio collars and released in the evening, after they had come round from the sedative.
The scientists tracked the cats at night using the radio-collars. This is the time of day that free-ranging cats are most active (although we know that owned cats adapt their routines to those of their owners).
Forty-three cats were captured for the study, almost all of them adults, and an equal number of males and females.
Most of the cats were of reproductive status, with five of the females being pregnant or lactating, and three other females having recently had kittens. 21% of male and 28% of female cats were sterilized, and these were mostly found near the site where the TNR group maintained a colony. The researchers did not sterilize any of the cats themselves, just in case any turned out to be owned cats.
Tests for disease found the cats were very healthy, with few getting positive results for the four infections. However, more than half had been exposed to Toxoplasma gondii at some point. This is higher than found in studies in other parts of the US. Other wildlife in the Chicago area was also found to have a high rate of T gondii exposure, including raccoons, skunks and coyotes.
Thirty-nine of the cats were fitted with radio-collars. It is sad to note that 20% of them (eight cats) died during the course of the study, although this is actually a much better survival rate than the scientists expected. Three were apparently killed by coyotes, two died after being hit by a vehicle, one died of disease, and it wasn’t possible to determine the cause of death of the other two deceased cats.
Another surprising finding is that almost a quarter of the cats were kidnapped, “removed from the system by cat advocates” who were opposed to the study. It is not clear what happened to these cats. Another 28% were legally adopted or removed, the transmitters expired for 13% of the cats, and there was no data on the remaining ten per cent.
Data showing the range of cats and coyotes is fascinating. In general the cats avoided the areas where the coyotes lived. While coyotes were mainly found in woods and natural landscapes, the cats lived mostly in urban landscapes. One single cat lived in an area surrounded by coyote habitat, and this was one of the cats that was sadly predated by a coyote.
One important finding to be drawn from this is that studies that estimate predation by feral cats probably overestimate it significantly if they fail to take account of coyote distribution. This is because the coyotes were living in the areas with most wildlife and the cats tended to stay in the more urban areas, around people.
This study suggests that coyotes are the reason cats tended to stay in urban landscapes, but it does not prove this is the reason. However, the authors note that other studies in areas without coyotes, do find free-roaming cats in natural landscapes.
This study shows that free-roaming cats are at risk from predation by coyotes, and owned cats would also be at risk. Are your cats indoors-only or allowed outside, and do you have coyotes where you live?
ReferenceGehrt, Stanley D., Wilson, Evan C., Brown, Justin L., & Anchor, Chris (2013). Population ecology of free-roaming cats and interference competition by coyotes in urban parks PLoS ONE, 8 (9) DOI: 10.1371/journal.pone.0075718