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  •  Cat Arithmetic on the fly (1+ / 0-)
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    And yes this is just arithmetic, not studies of predation on small populations of rare/endangered/threatened species, etc., etc. But the American Bird Conservancy is doing the same kind of arithmetic.

    Humane Soc US Aug 2011 estimate is 68 million owned cats
    1997 estimate by Humane Soc was that 35% of cats were strictly indoor cats, so let us posit (68 x 0.65) = 44 M owned cats allowed outdoors to some degree
    Various sources estimate 50 M feral cats
    So: 50 M ferals + 44 M owned cats = 95 M cats in the U.S., half of them 24/7, half of them out, say, 30% to 80% of the day??

    * * * * * * * *
    U of Georgia KittyCam project: 55 cats w/ kitty cams allowed outdoors for 7-10 days, yielding 2000 hours of video.
    44% of the cats (24) hunted and 30% of them caught an average of 2.1 animals per week
    13% of the prey were birds, so 55 cats caught 5 birds/week = 4.72 birds killed per cat-year

    KittyCam arithmetic
    95 M cats x 4.72 birds = 450 M bird kills per year by cats assuming human population density of 851/sq mi., temperate Southeast habitat.

    So far I haven't yet been able to get past the Cam glitz to their methodology, e.g., how they selected the cats, neighborhoods, cat population density, time of day and how many hours per day the cats were outdoors, density of bird feeders, etc. These factors, plus whether you live in the summer or winter grounds of rare, endangered, or threatened species, all play into the ethics of allowing cats some outdoor time each day. Where I live, you will not notice the dent my cats might put in the rodent and bug population. There are no R/E species of any kind except a breeding pair of kestrels (woo hoo!!). We have bluebirds, meadowlarks, and turkeys galore. I only feed the hummingbirds now that I have 6 young cats, no seed feeders.

    The higher the density of cats, the higher-quality bird habitat, the more kills you're likely to get (granted, at some point, population density gets so high that concrete might crowd out habitat and kills per cat-year might well decline. Manhattan population density is 27,000/sq mi, average U.S. pop density is 89/sq mi.)

    KittyCam study was done in Athens-Clarke County (Georgia) consolidated city-county, which has a population density of 851/sq mi. This is comparable to the closest town to my house, 804/sq mi in a county averaging 150/sq mi. It's more like 70/sq mi where I live, with max cat density of 10-15/sq mi., easily 3 times more dogs. Compare this to Nashville at 1200/sq mi in a county of 1134/sq mi, Raleigh NC at 2916/sq mi and its suburbs averaging about 1700/sq mi, Seattle 7400/sq mi in a county of 900/sq mi, Portland ME at 3106/sq mi in a county of 337/sq mi.

    KittyCam data on prey squared with my results: voles and lizards are the major prey in Southeast/Mid-Atlantic

    * * * * * * * *
    raincrow data
    My data, normalized to 55 cats in mostly suburban settings, 800-2000/sq mi, based on observed kills, remains littering porches, carpets, lawns, driveways, etc. Significantly fewer prey were brought home in my data set than in the KittyCam data, say < 10%. Unlike KittyCam 7-10 day observations, my data are 2-18 years per cat, and show definite change in hunting avidity, preferred prey, and success across cat lifetime. Young cats took more varied prey overall, then settled into mostly voles and mice with age -- except the most avid hunters who were still bagging chipmunks and even rabbits in their teens. Males rescued after lengthy abandonment were more often the big game hunters. Small to medium-sized females most often the heartbreaking "bird specialists."

    raincrow arithmetic
    85% = 47 cats together killed 34 birds/year
    8% = 4.4 cats @ 15 birds/yr = 66 birds/year
    7% = 3.9 cats @  2.5/yr = 10 birds/year

    So 55 cats killed 110 birds/yr

    95 M cats x 110 birds/yr = 190 M

    Clearly this is not an order of magnitude difference, but it is NOT KittyCam's estimate of 450 M, or American Bird Conservancy's and estimate of 500 M to 1 B.

    * * * * * * * *
    Various estimates, including by U.S. Fish & Wildlife, put the U.S. breeding population of birds at a minimum of 10 billion and the fall population at 20 billion.

    “Five billion birds die in the U.S. every year,” said Melanie Driscoll, a biologist and director of bird conservation for the Gulf of Mexico and Mississippi Flyway for the National Audubon Society.
    This includes uncounted millions of baby birds from trauma during fledging; predation; poor habitat, food availability; etc.

    Major categories of human-caused bird deaths:
    Pesticides:      72 M directly, unknown numbers die later along with orphaned chicks
    Power line kills: 174 million, U.S. Fish & Wildlife estimate
    Glass and building strikes: 500 M to 1 B
    Tower strikes:    50 M
    Car strikes:    60 M
    Wind generator strikes:  75k to 275k

    860 M to 1.36 B human-caused, call it 1.1 B to get a middling number for human-caused bird kills
    5 B - 1.1 B = 3.9 B birds killed by non-human causes

    Of that 3.9 B per year, if 190 M are caused by cats, cats cause on average 5% of total annual kill due to non-human causes.
    Of the total 5 B bird deaths per year, if 190 M are by cats, cats cause an average of 3.8% of total kill from all causes.

    190M cat kills / 10 to 20B birds total = 0.8 to 1.9% of the total U.S. bird population killed by cats per year.


    by raincrow on Wed Jan 23, 2013 at 09:26:15 PM PST

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