by Merritt Clifton
CLEVELAND, Ohio––Deer don’t eat cats, or cat poop, but that did not stop the American Bird Conservancy from alleging in a December 23, 2014 media release that feral cats are the “likely source” of the parasite Toxoplasma gondi, discovered in about 60% of the 444 deer and 65% of the 200 cats tested in the Cleveland suburbs by Gregory Ballash and team of the Ohio State University Department of Veterinary Preventive Medicine.
“Similar estimates for white-tailed deer infections have been found in Iowa (53.5 -64.2%), Pennsylvania (60%), Mississippi (46.5%), and in [previous studies done in] Ohio (44%), suggesting widespread environmental contamination,” wrote American Bird Conservancy publicist Robert Johns.
No historical context
Absent historical information about the prevalence of Toxoplasma gondi in deer several decades ago, and in the mid-19th century and earlier, before domestic cats were broadly distributed throughout North America, there is only an increasingly weak circumstantial link to suggest that domestic cats have had anything to do with what Ballash et al found.
Asserted Johns, “Cats, both domestic and wild (e.g., bobcats), play a critical role in the spread of toxoplasmosis because they serve as the definitive hosts, fulfilling the requirements needed for the parasite to sexually reproduce and complete its life cycle.”
Further, in the Ballash study, Johns wrote, “The odds of deer from urban locations testing positive for toxoplasmosis were nearly three times those of deer from suburban reservations when adjusted for age and gender. The study found that densities of human households, and likely cats, were a significant predictor of infection in deer.”
But the density of human households and the density of cats are often not the same, for example in neighborhoods of pet-restricted apartment houses and condominiums.
Neither does the density of indoor pet cats, about 70% of the total cat population, necessarily parallel densities of free-roaming pet cats and, especially, feral cats. Feral cats tend to congregate in locations such as the vicinity of dumpsters and food-processing facilities whose waste attracts plentiful rodents. These are often far from residential areas.
Finally, areas with high human population density may also have other sources of Toxoplasma gondi, which travels in many ways other than through the distribution of oocysts in the feces of cats, bobcats, pumas, and other felines.
Parasite of obligate carnivores
The disease toxoplasmosis, caused by Toxoplasmosa gondi, infects humans and most other species primarily through eating tainted meat.
The full life cycle of Toxoplasmosis gondi was for about 50 years widely believed to occur only in domestic cats, but it is now known to occur in any feline.
However, Toxoplasmosa gondi has also been found in many habitats with few if any felines––especially remote oceanic habitats.
Why doesn’t the full life cycle of Toxoplasmosa gondi occur in species other than felines? The simple answer is that it may, but science has yet to identify the other carriers.
Why has Toxoplasmosa gondi not adapted itself to go through its full life cycle in other land animals of historically similar distribution and habits to felines, such as foxes, coyotes, jackals, and dogs, many of whom have long been more abundant within their normal range than felines of any sort?
Sea otters & anchovies
The missing link, emerging in pieces since 2008 from investigations of Toxoplasmosa gondi in California sea otters, which initially blamed cats, may be anchovies, first canned and marketed as cat food circa 1930, about 25 years before the first putative connection was established between Toxoplasmosa gondi and domestic cats.
The production of anchovy-based cat food stopped during World War II, 1939-1945, but took off explosively from the mid-1950s on. It was in the 1960s and 1970s, 30 to 40 years after anchovy-based cat food first appeared in grocery stores, that the Toxoplasmosa gondi link to cats was confirmed.
One of the main areas of anchovy harvest for the cat food industry (and for that matter the pizza industry) was off the California coast, entirely overlapping the range of California sea otters, like cats an obligate carnivore, now known to be frequently infected with Toxoplasmosa gondi.
Eventually the anchovy population of the region crashed and the fishery collapsed with it, followed by a decline of the sea otter population in recent decades, after sea otters had slowly recovered from aggressive fur hunting that was ended by law in 1911.
The coastal mainland in this area is among the most arid parts of California. Sparsely populated by humans and pet and feral cats because of the lack of water, this portion of coast has so little runoff that the likelihood of cat litter ever washing into sea otter habitat is slim. Cat feces could spread to coastal sea water in places north of Monterrey and from Santa Barbara south, but almost certainly not in between.
Initially the cooking process that goes into canning was believed to kill any & all pathogens that might contaminate canned pet food, or anchovy pizzas, but over time this has proven to be not the case with a variety of particularly hardy agents.
Did Toxoplasmosa gondi come to cats via anchovies, and is this relatively recent origin of widespread Toxoplasmosis gondi in cats why other land animals have not come to host the full life cycle of their own endemic forms of Toxoplasmosa gondi?
Search for a marine host
Given the current early state of the research, no one can really pretend to know yet. The search for a marine host has barely begun.
As anchovies are a major part of the diet of practically all marine mammals other than baleen whales (who undoubtedly ingest some), and polar bears, and have probably been widely distributed throughout the world’s oceans for far longer than most mammals have existed, this would explain the recently identified widespread distribution of Toxoplasmosa gondi among gray seals, ringed seals, monk seals, sea otters, and perhaps other species whose normal habits don’t put them anywhere in proximity to felines, either domestic, feral, or wild.
Inflated cat counts
The most glaring weakness in the American Bird Conservancy attribution of Toxoplasmosa gondi in deer to the presence of cats, however, was the claim of ABC founder and president George Fenwick that “The number of domestic cats in the U.S.—both owned and un-owned—has increased to as many as 188 million,” who “are killing 2.4 billion birds and 12.3 billion mammals each year.”
Interestingly enough, Fenwick cited somewhat lower numbers for cats and their alleged prey than he did two years earlier.
Then, in January 2013, the American Bird Conservancy ballyhooed a literature review by Smithsonian Conservation Biology Institute ornithologists Scott Loss and Peter Marra and U.S. Fish and Wildlife Service biologist Tom Will, who alleged in the journal Nature Communications that domestic cats in the U.S. kill up to 3.7 billion birds per year and as many as 20.7 billion mice, voles, and other small mammals.
Loss, Marra, and Will derived these projections by overstating the U.S. pet cat population by ten million, the outdoor pet cat population by closer to 50 million, and the best documented estimates of the feral cat population by up to 64 million.
Thus Loss, Marra, and Will argued that cat predation on birds is magnitudes of order higher than the estimate of 100 to 125 million birds killed by cats per year issued by Albert Manville of the U.S. Fish & Wildlife Service in 2002, previously considered the most credible.
Outdoor cat population declining
The U.S. pet cat population is down 18% from the 2007 peak of nearly 90 million, and is now 74 million and still falling, according to the 2012 edition of the American Veterinary Medical Association Pet Ownership & Demographics Sourcebook.
Pet keeper surveys have shown since 1990 that more than two-thirds of U.S. pet cats are kept indoors.
Loss, Marra, and Will guesstimated that there are between 30 and 80 million “unowned” cats in the U.S. In the past 22 years, however, no survey of animal control data, roadkill counts, or nationally representative sampling of feral cat habitat has shown any likelihood that the feral cat population exceeds 16 million.
I have estimated since 2003, from the combination of available data sources, that the annual midsummer peak of the feral cat population is steady at less than 13 million, the winter low is just over six million, and the year-round average is about nine million.
Tufts University School of Veterinary Medicine graduate student Anne Fleming, at a December 2012 conference on outdoor cats hosted in Los Angeles by the Humane Society of the U.S., presented data from surveying 263 feral cat colonies in Rhode Island which projects a national feral cat population of 8.8 million.
The most thorough of many critiques of the Loss, Marra, and Will claims came from Vox Felina blogger Peter Wolf.
Recounted Wolf, “On May 25, 2011, J. Scott Robinson, director of the Office of Sponsored Projects for the Smithsonian Institute, sent a three-page proposal to Randy Dettmers, a biologist in the Division of Migratory Birds for the U.S. Fish and Wildlife Service, outlining the scope and budget for a project called ‘Effects of subsidized predators on bird populations in an urban matrix.’ The work was to begin in just one week and continue through the end of September, conducted by Smithsonian Conservation Biology Institute researchers Peter Marra and Nico Dauphiné. Two weeks earlier, on May 11, 2011, Dauphiné had been arrested, charged with attempted animal cruelty for trying to poison neighborhood cats.”
Convicted in District of Columbia Superior Court of misdemeanor attempted cruelty to animals on October 31, Dauphine was on December 14, 2011 sentenced to do 120 hours of community service, spend a year on probation, and pay a fine of $100, with 180 days in jail suspended.
“Killer cat study”
“Fast-forward a year and a half,” Wolf continued, “to the recent publication of the Smithsonian’s ‘killer cat study.’ If, as [bird population researchers] T.W. Arnold and R.M. Zink have suggested, the breeding population of North American landbirds is 4.9 billion, then the 1.4 to 3.7 billion mortalities reported by Loss et al represent an astonishing 28.5–75.5% of the total population. That’s on top of the 21% that Arnold and Zink attribute to collisions with towers and windows. While some species are, unquestionably, on the verge of extinction, the entire population of North American landbirds most certainly is not.”
Further, Wolf wrote, “Loss et al fail to acknowledge that predation—even at very high levels—does not necessarily lead to population-level impacts. Like all predators, cats tend to prey on the young, the old, the weak, or unhealthy. As the British Royal Society for the Protection of Birds notes: ‘Despite the large numbers of birds killed, there is no scientific evidence that predation by cats in gardens is having any impact on bird populations United Kingdom-wide…It is likely that most of the birds killed by cats would have died anyway from other causes before the next breeding season, so cats are unlikely to have a major impact on populations.’”
Loss, Marra, and Will noted that cats have been found to prey upon at least 58 U.S. native bird species. Observed Wolf, “57 of the 58 species have been given a ‘Least Concern’ conservation status by the International Union for Conservation of Nature.”
Wolf also obtained a brief critique of the Loss, Marra, and Will paper from Dennis Turner, editor of The Domestic Cat: The Biology of its Behaviour.
“Such extrapolations of how many birds or rodents or reptiles and amphibians cats kill each year are absolutely meaningless on the species level if not put into context with the annual production of that species,” said Turner. “Any claim that cats are a much ‘more significant anthropogenic threat’ than other factors (e.g., construction with loss of habitat, pollution, road traffic kills, etc.) are even more ridiculous, in that there are rarely estimates (good or poor) of deaths of birds/mammals/amphibians to such factors to compare with.”
Ironically, Loss, Marra and Will recently reached a similar conclusion, Wolf recalled, in a 2012 paper published in the journal Frontiers in Ecology and the Environment. There, Loss, Marra, and Will acknowledged, “Quantification of direct anthropogenic mortality, although critical for conservation efforts, remains imprecise. National mortality estimates are often based on extrapolation from a limited sample of small-scale studies, and estimates of uncertainty are ignored or only superficially assessed.”
While Loss, Marra and Will argued that the U.S. outdoor cat population is increasing, a variety of studies done since 1908 suggest that the combined totals of outdoor pet cats and feral cats have actually been quite consistent. Frank M. Chapman of the American Museum of Natural History produced the first estimate, putting the outdoor cat population at circa 25 million. National Family Opinion founders Howard and Clara Trumbull did surveys in 1927, 1937, and 1947-1950 that showed the outdoor cat population gradually rising from about 30 million to 35 million.
I found in national surveys of cat feeders and rescuers done in 1992 and 1996 that the combined outdoor pet and feral cat population had probably peaked circa 1991 at about 46 million, and was in rapid decline.
Shelter admissions of cats dropped by about 75% during the 1990s, after the introduction of neuter/return to the U.S., before leveling off at about four million per year during the past decade.
Oldest colony is zeroed out
Loss, Marra and Will contended that neuter/return has not reduced feral cat numbers just five weeks after Inayat Singh of Canadian Press reported that neuter/return had eliminated possibly the oldest feral cat colony in North America.
Living behind Parliament Hall in Ottawa, above the Rideau Canal, the cats were reputedly descended from cats brought by British engineer John By, who built the canal in 1826-1832. Ottawa was originally called Bytown in honor of By. From completion of the first Parliament building in 1866 until 1955 the cats wandered the halls of Parliament as quasi-official mousers.
After eviction, the cats persisted on Parliament Hill, fed by volunteers coordinated by Irene Desormeaux, who died in 1987. Neuter/return was begun by her successor, Rene Chartrand. About 30 cats were sterilized. Chartrand retired for health reasons in 2008, replaced by former civil servant Brian Caines and half a dozen volunteers. The last kittens in the colony were born “probably 10 to 15 years ago,” Caines told Singh of Canadian Press.
With just four cats left, Caines found adoptive homes for three, and adopted the last cat himself.
Chartrand died on December 7, 2014.
Cats & wind power
Meanwhile back in Foggy Bottom, as Washington D.C. became known back when most of the region that is now the D.C. metropolis was still just frequently flooded waterfowl habitat, inflated claims about cat predation on birds may have given the U.S. Fish & Wildlife Service political cover in December 2013 for granting a 30-year exemption from prosecution to wind power developers whose turbines kill eagles.
The exemption was announced two weeks to the day after Duke Energy Renewables agreed to pay $1 million in settlement of charges resulting from the deaths of 14 golden eagles and 149 other protected birds at wind farms near Casper and Campbell Hill, Wyoming between 2009 and earlier in 2013.
Wind turbines in the Altamont Pass east of the San Francisco Bay area in California are believed to kill about 60 bald and golden eagles per year. Other wind farms around the U.S. are known to have killed at least 67 eagles since 2008.
At the same time as granting the exemption for killing eagles, the Fish & Wildlife Service approved a plan by Beech Ridge Energy to minimize and mitigate the effects of a southern West Virginia wind farm on endangered bats and birds.
American Bird Conservancy president Fenwick and National Audubon Society president David Yarnold immediately denounced the exemption for eagle deaths.
The American Bird Conservancy also rushed to amplify a projection by Loss, Will, and Marra that wind turbines are already killing 140,000 to 328,000 birds per year, and may kill as many as 1.4 million birds per year by 2030.
The Loss, Will, and Marra projection was seven to sixteen times higher than most previous estimates of mortality among birds caused by wind turbines, but much lower than estimates of 440,000 projected by Albert Manville of the Fish & Wildlife Service in 2009 and 573,000 projected by California ecologist K. Shawn Smallwood earlier in 2013.
But after Loss, Will, and Marra had alleged that domestic cats in the U.S. kill up to 3.7 billion birds per year, even their high estimate of bird losses to wind turbines looked small.
“For several years now, the National Audubon Society and American Bird Conservancy have co-opted, twisted, and misrepresented any scrap of published science they could find—however indefensible—suggesting that cats might have an impact on bird populations,” commented Peter Wolf. “But what if their campaign has been too effective—with the wrong audience?”
Acknowledged Wolf, “Unfortunately, there is no way to tell if all of this campaigning against free-roaming cats and TNR had anything to do with [the Fish & Wildlife Service eagle decision] which, sadly, will likely mean the deaths of more eagles. But seen against the alleged impacts of cats, wind turbines seem utterly benign.”
Cats & coyotes
The most recent major study of cat impact on wildlife, published just a few months earlier, concluded that “Estimates of the ecological impact of cats, extrapolated over large geographic areas, are likely to overestimate the impact of cats if the effects of interference competition by coyotes are not considered.”
Entitled “Population Ecology of Free-Roaming Cats and Interference Competition by Coyotes in Urban Parks,” the study by wildlife ecologists Stanley D. Gehrt, Evan C. Wilson, Justin L. Brown, and Chris Anchor appeared in the September 13, 2013 edition of the online journal PlosOne.
Gehrt et al “focused our research on free-roaming cats inhabiting patches of natural habitat within the northwestern suburbs of the Chicago metropolitan area,” they wrote.
They trapped and radiotagged 43 cats in all.
Gehrt has continuously monitored radio-collared coyotes at the seven study sites since 2000. Thirty-three coyotes were known to be using “all or portions” of the study sites while the cat research was underway.
Cats prove healthy
“In general,” Gehrt et al said, “we found that free-ranging cats were in better condition than we expected, with a relatively high survival rate and low exposure to cat-related pathogens, with the exception of Toxoplasmosa gondi. There was little evidence that transmissible diseases were important.” Blood testing “indicated low exposure to FIV and FeLV.”
Gehrt et al noted “potential for cats to negatively impact other species, including humans, through their transmission of Toxoplasmosa gondi.”
But Toxoplasmosa gondi is already widely distributed among other mesocarnivore species in the Chicago metropolitan area, Gehrt et al acknowledged, without visibly harmful effect.
About 60% of the striped skunks, 38% of the raccoons, and up to 63% of the coyotes in the vicinity are seropositive for toxoplasmosis gondi, according to other research by Gehrt.
“Our results support the notion that the ecological impact of cats in natural habitat fragments is minimized due to interference competition from coyotes,” Gehrt et al wrote. “Consequently, the ecological impact of cats in those areas, via predation of native species, also was likely limited.”
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