Analysis of the impact of TNR programs on populations of feral cats

I’m looking at two sets of data in this article. The first one that I refer to comes from the University of New South Wales in Sydney, Australia. They commenced a TNR program to manage the population of about 69 unowned urban cats on their campus. The programme proved successful. Obviously, this pleases me. You can see the comparison between their programme and other programs in the chart below. I’ll discuss this briefly but by all means make your own conclusions.

Comparisons of outcome data from similar TNR studies
Comparisons of outcome data from similar TNR studies. My thanks to NSW Uni. Click the image to see a larger version.
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The university’s TNR program lasted for nine years. The original number of cats was 69 as mentioned. 34 cats came into the group and 19 cats were born on site. Therefore, the total managed was 122. At the conclusion of the nine-year TNR program 15 cats remained. That is 12% of the total number of cats. 30 cats were rehomed and 17 were euthanised. 12 cats died and 29 cats disappeared.

RELATED: 15 facts about a 23-year TNR program in Florida.

Taking up the numbers from another study headed “Levy” which I believe is the name of the lead author in the report, the TNR program lasted for 11 years. The original number of cats was 155. The number of cats remaining within the colony managed was 23 at the end of the programme or at the time of measuring the outcome of the programme. That represented 15% of the total managed. 47 cats were rehomed and 11 were euthanised. Six died and 21 disappeared.

The conclusion from that shard is quite clear namely that TNR has been successful in these programs.

By contrast, an AVMA study titled Analysis of the impact of trap-neuter-return programs on populations of feral cats, concluded that TNR “did not indicate a consistent reduction in per capita growth, the population multiplier, or the proportion of female cats that were pregnant”. In other words, I take that to mean that the TNR programs did not result in a reduction in the number of cats. However, it also indicates that the colonies were stable in number, i.e. they were not growing. The programs were assessed from 1992 to 2003 in San Diego County, California (n = 14,452), and from 1998 to 2004 in Alachua County, Florida (11,822).

This may indicate that there is a variation in success rates due to how the TNR programs are conducted which brings me to the next point.

The study also referred to the potential benefits of scientifically measuring outcomes of TNR programs. I would agree with that. I would like to see some more charts and data on the outcome of many more feral TNR programs especially in America. This would help to improve TNR programs. The information would help local authorities to decide whether to support them or not.

RELATED: Intensifying TNR in an area reduces shelter cat impoundment.

On the basis of the chart above, if TNR outcomes are successful, it would help to promote more TNR programs and to silence critics. Ornithologists have historically criticised TNR programs for failing because they put feral cats back into the environment where they prey on birds. The chart above indicates reductions in feral cat numbers and therefore less predation on birds.

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