
(Beth Clifton collage)
Too few cats around bird feeders means pine siskins die by thousands
SACRAMENTO, California––When are free-roaming cats watching a bird feeder the birds’ best friend?
When infectious disease is at large among common bird feeder species, spreading rapidly from bird to bird in the absence of predators to kill and consume the sick and disabled.
Many mid-sized predators can do the job, before a feeder-spread disease drops birds by the hundreds, thousands, or tens of thousands, but such candidates as hawks, owls, eagles, foxes, raccoons, and fishers are much less well adapted to live and hunt in yards and on porches than cats.
Feral cats in particular do most of their bird-hunting after dark, when only sick and injured birds are still on the ground beneath bird feeders.


Dr. Cat made house calls
The value of this prophylactic cat service to bird populations has seldom become more evident than among pine siskins in the winter and early spring of 2020-2021.
A seasonal shortage of pine cones in the Canadian range of the pine siskin has caused this small member of the finch family to congregate in rarely seen numbers around bird feeders along the U.S. west coast, from Puget Sound all the way to southern California.
A scarcity of free-roaming cats, gradually developing over the past thirty years, may be among the major contributing factors behind outbreaks of salmonellosis among displaced pine siskins, reported most often in communities with some of the oldest and largest neuter/return programs in the United States.
“Since December, the California Department of Fish and Wildlife (CDFW) and wildlife rehabilitation centers have been inundated with calls from residents who are finding sick or dead finches at bird feeders,” CDFW senior environmental scientist Krysta Rogers and communications officer Ken Paglia announced on February 8, 2021.
“Most reports have come from locations on California’s Central Coast, the San Francisco Bay Area and Sierra Nevada communities,” Rogers and Paglia said then.


How bird feeders kill birds
A March 8, 2021 update was considerably more specific. Rogers and staff had by then logged more than 2,000 songbird death reports, mostly of pine siskins, “along with a small number of goldfinches,” they added.
A closely related species, goldfinches often feed alongside pine siskins.
The California Department of Fish and Wildlife “determined the birds are contracting salmonellosis, a disease caused by salmonella bacteria, by sharing bird feeders with other infected avian species,” Rogers told media.
“When there is a disease circulating in the population,” Rogers explained, “bird feeders ensure the birds remain in really close contact with one another, as well as other bird species, as they share the feeder.”
“Bird feeders also keep the birds in one location for longer periods of time,” Rogers added, “allowing feces to build up. If there are sick birds in that group, they will shed the salmonella bacteria in their feces, contaminating the area, leading to more and more birds becoming sick and dying from the infection as they try to access the feeder or feed on the spilled seeds under the feeder.


“Remove the bird feeders”
“The most effective way to slow the spread of this infection and reduce mortality,” Rogers emphasized, “is to remove the bird feeders, because that is primarily where this disease spreads.”
Rogers said nothing about cats, but the numbers she shared did.
Note that each number of confirmed bird deaths probably represents thousands of dead birds whose remains were not retrieved and tested.
Sonoma County, reporting 238 bird deaths from salmonellosis, has had active feral cat neuter/return programs in the largest cities in the county since 1990.
Santa Clara County, reporting 231 bird deaths from salmonellosis, had enough active feral cat neuter/return programs, sterilizing and vaccinating enough cats, that in 1993-1994 it was the location of one of the first major studies of the efficacy of the neuter/return method.


Home of Project Bay Cat
Marin County, reporting 173 bird deaths from salmonellosis, has also had neuter/return programs for nearly 30 years, with central coordination of the programs since 2005.
Contra Costa County, reporting 150 bird deaths from salmonellosis, had multiple active neuter/return programs by 1998.
San Mateo County, reporting 143 bird deaths from salmonellosis, had scattered independent neuter/return programs in the 1990s, with central coordination of the largest programs since 2000. The best-known San Mateo County neuter/return program, Project Bay Cat, began in 2004.
(See Ceasefire halts cat shootings in East Bay Regional Parks––for now.)


More dispersed in breeding habitat
Santa Cruz County, reporting 115 bird deaths from salmonellosis, has also had scattered neuter/return programs since the 1990s.
Alameda County, reporting 109 bird deaths from salmonellosis, has had neuter/return programs of significant size since 1994.
Sacramento County, reporting 109 bird deaths from salmonellosis, has had some neuter/return activity since the early 1990s, with larger projects at least since 2004.
Placer County, the most sparsely populated county among the nine reported salmonellosis hot spots, has had 72 confirmed bird deaths from the disease. Active neuter/return work has been underway in Placer County at least since 2012, but very likely began much earlier.
Finished Rogers, “Most salmonellosis outbreaks [among pine siskins] end when the pine siskins return to their breeding grounds, typically late March or April. In their breeding grounds, pine siskins are more dispersed for activities like nest building and raising chicks, so infection tends to be less common.”


Salmonellosis outbreak hit Lynnwood first
On January 8, 2021, exactly one month before Rogers issued the first warning of the salmonellosis outbreak hitting pine siskins, the disease outbreak was observed by the Progressive Animal Welfare Society, of Lynnwood, Washington––which, coincidentally, was circa 1990 among the very first established humane societies to introduce a neuter/return program.
“The large flocks [of pine siskins] we are seeing all over Western Washington are incredible to witness,” the Progressive Animal Welfare Society acknowledged on Facebook.
However, the posting continued, the PAWS Wildlife Center had admitted 68 pine siskins in 60 days, and was receiving multiple calls about sick siskins every day.


“Wash all nearby surfaces”
“Usually, we recommend removing feeders for a few weeks when a sick bird is found nearby and cleaning the area thoroughly,” the Progressive Animal Welfare Society advised.
“However, the flocks are so large and cases so frequent right now, “ PAWS continued, “that we recommend removing your feeders even before you detect a sick bird, until the irruptive migrants move on.”
The Progressive Animal Welfare Society also recommended that bird-feeding individuals should “Wash all nearby surfaces,” with a 10% bleach solution, “and rake the ground around the feeder,” wearing gloves whenever possible and washing hands often, since “humans can contract salmonella too.”


Mycoplasma gallisepticum
Observed Program for Monitoring Emerging Diseases wildlife disease moderator Pablo Beldominico, “Bird feeders also facilitate the spread of mycoplasmosis among birds that use them.”
Indeed the feeder disease mycoplasma gallisepticum should have impressed upon bird-feeding enthusiasts a valuable lesson about the ecological importance of the free-roaming cats they frequently curse, and often trap and kill, shoot, or poison, when they see cats with birds in their mouths, or find the remains of birds they believe were killed by cats.
Alley Cat Allies president and founder Becky Robinson, with Louise Holton, who later founded the Maryland organization Alley Cat Rescue, together introduced the neuter/return technique to Washington D.C. and surrounding suburbs in 1990.


Outdoor cat population crashed
Data collected by then-Calvert Animal Rescue League executive director Phil Arkow showed that in 1992 Maryland shelters killed 85,600 homeless cats.
Similar data is not available for Washington D.C. itself, nor for the Virginia side of Washington D.C., but the Maryland data is likely generally indicative of the abundance and ecological significance of free-homing cats in the region at the time.
Within five years the Maryland shelter cat death toll dropped to 58,000. By 2000 it was down to circa 30,000, and as of 2016 had declined to about 14,200.
Outbreaks of mycoplasma gallisepticum meanwhile exploded around local bird feeders––possibly because cats were no longer killing sick birds before they could spread the infection.


Originally known as factory-farmed turkey disease
Before the mid-1990s, mycoplasma gallisepticum was most closely identified with outbreaks on factory-style turkey farms, which had arrived in the outer Washington D.C. area 10-20 years earlier.
Between the early 1990s and the mid-2000s, mycoplasma gallisepticum spread up and down the east coast and across the U.S. as a bird feeder disease.
Each major outbreak followed several years after the debut of big neuter/return programs in the vicinity.


(Beth Clifton collage)
Edward Howe Forbush
Antipathy toward free-roaming cats as bird predators has been whetted by birding organizations since the 1916 publication of The Domestic Cat: Bird Killer, Mouser and Destroyer of Wild Life; Means of Utilizing and Controlling It, by Edward Howe Forbush, the 19th and early 20th century Massachusetts state ornithologist whose inveterate hatred of cats was based largely on his own scientific ineptitude.
Among other conspicuous errors, Forbush wrongly blamed cats who were never there in the first place for the decline of roseate terns on Muskeget Island, later established to have been caused by gull predation; claimed birds do not prey on other birds; conflated the Quebecois slang term for raccoons, chat sauvage, and descriptions of raccoon behavior, with second hand anecdotal accounts of cat behavior; and conflated bobcats with domestic cats.
Forbush nonetheless furnished the quasi-scientific basis for more than half a century of concerted efforts by hunters and birders to add cats to state lists of legally hunted species.
The Forbush tract continues to be the usually unacknowledged template for the Nature Conservancy, National Audubon Society, and American Bird Conservancy policies of opposition to neuter/return feral cat control.
(See How a birder’s mistakes incited 100 years of cat hatred.)


Predation vs. disease
But an accurate understanding of the ecological role of predation includes recognizing that except on isolated islands, predation is rarely if ever a significant cause of lasting prey species population declines.
This is for two reasons.
First, almost all animal predation is “compensatory,” meaning that the predators kill and eat mainly the sick and injured, the aged and infirm, and unattended young, none of whom are likely to contribute any more to the reproductive success of their species than they already have.
Most animals killed by predators would not survive for much longer anyhow. Especially if the victim animal is suffering from a contagious disease, like pine siskins afflicted with salmonellosis, predation tends to help the species far more than would the temporary survival of an individual who might infect many others.


Only “additive” predation actually reduces the long term abundance of the prey species, and then only under rare circumstances.
“Additive” predation, including by parasites and disease-carrying bacteria, cuts into the successful breeding population of the prey species, but seldom occurs for long, because if the prey population declines, the predators, including pathogens, starve out long before the prey or host species disappears entirely.
I am curious, why is it OK for cats to kill wild birds but NOT ok for pit bulls to kill cats?
The pit bull pattern of random unprovoked attacks on healthy animals and humans, including other pit bulls, not for consumption or self-defense, but simply because the victims are there, is the behavior of a deranged serial killer, not that of a natural predator. There is no analogy to pit bull behavior in normal predator/prey relationships.
The natural predators of feral cats include coyotes, fishers, and foxes. Hawks, owls, and eagles also occasionally prey on feral kittens. (See Coyotes: nature’s animal control officers and Are Southern California coyotes eating 68% fewer cats than 20 years ago?.)
Good article! Just wanted to add that dominant tom cats can be a substantial predator of feral kittens – especially in colonies or neighborhoods that have unstable cat populations (high turnover) due to trap/kill programs, natural predators or heavy outdoor poisoning of rodentia. Some toms will then seek and kill kittens not from their own gene pool. Anecdotally I see this more in rural agricultural colonies but have seen some reports from urban colonies as well.
Thanks, Dave. Beth and I have also observed tom cats killing kittens, especially in rural areas, but in our observation, the dominant toms tend to protect their own offspring, while the kitten-killers are most often roving interlopers, trying to take over a dominant tom’s territory and queens.
Cats are notorious for killing animals for sport; if this were not true, well fed house cats would not catch animals. Previous indoor only cats I have had caught mice a couple times but did not eat them. Domestic dogs are the same. I have no doubt my dogs would LOVE to kill squirrels, rabbits, cats, deer my dogs are not starved; it’s just their instinct. It’s the instinct of pit bulls to kill cats. I am no fan of pit bulls or outdoor cats but it feels a little bit disingenuous to excuse one but not the other. I am almost positive that if birds could speak, they would refer to cats as “deranged serial killers.”
You are overlooking the most essential & obvious behavioral difference between fed domestic house cats, whom ANIMALS 24-7 recommends keeping confined, away from wildlife, and feral cats, who are not fed by humans, and hunt for a living. Cats who hunt for a living hunt rodents, by night, or sick and injured birds who are still on the ground after nightfall. These cats are so seldom seen by humans that many humans have no idea of their presence. Nocturnal hunting, primarily for rodents, maximizes the cats’ caloric return relative to calories expended, and minimizes their exposure to humans, dogs, and other diurnal threats.
Fed cats, on the other hand, like well-fed humans, can afford to go sport hunting, which involves a tremendous expenditure of calories relative to caloric return. Indeed, only about one cat in 10 has the vertical visual acuity to follow a bird who takes flight, & you can test this yourself with a wad of paper tied to a string. Every cat will follow the paper easily when moved horizontally, but most cats will lose sight of it as soon as it is suddenly jerked above their head level, like a bird springing into the air.
Fed cats often become sport hunters by daylight, if allowed the opportunity to do so, and do opportunistically hunt birds, but this occurs because being fed tends to significantly alter normal cat behavior.
Also, this just came out:
https://www.smithsonianmag.com/science-nature/australias-cats-kill-two-billion-animals-annually-180977235/
2 billion is a very deranged sounding number.
Indeed, two billion is a very deranged sounding number, resulting from a deranged method of compilation, designed to support the Australian government’s century-plus-long succession of very well funded but thus far wholly futile campaigns to eradicate feral cats, as the alleged causes of losses of species resulting primarily from destruction of wildlife habitat.
Along the way, the official Australian estimates of the numbers of animals killed by cats at large have exploded, more-or-less proportionate to the amount of opposition the cat extermination policies have encountered in recent years.
Yet the estimates of the numbers of cats at large have fallen from circa 20 million in the mid-1990s, to 15 million circa 2000, to just 2.8 million now, along with 2.6 million owned cats now, 90% of them sterilized. (See https://aiam.org.au/resources/Documents/2001%20UAM/PUB_Pro01_SusieChasling.pdf.)
Pit bulls do not just kill cats who may be the animal companions of humans (how will you or the dog know the difference?), but kill other dogs, especially small ones, and humans. I and my small dog, who is 9.2 pounds, have been attacked countless times by large dogs, and 50 or more percent of the time it has been by pit bulls. Fortunately we avoided injury. I had to call the police twice and carry a mace gun. Also in most areas there is a leash law, and all dogs that attacked were off the leash.
Sharing to socials with gratitude, frustration, rage (including at the poster above) and continuing determination.
Superb reporting as usual. So just to clarify, does this mean it’s OK to allow a housecat to go outside (bird kills being one of the traditional reasons against it)?
thanks.
ANIMALS 24-7 does not recommend allowing house cats to roam. Neither do we recommend feeding either free-roaming cats or birds in a manner that upsets the local ecological balance.
If birds are fed in a manner that causes them to congregate in abnormal density, however, which is very often the case, the cats they attract are a part of nature trying to balance itself.
What we do recommend for house cats, where practicable, are “catios,” or high-fenced outdoor areas with overhanging fences from which cats cannot escape, within which they can pursue normal cat behavior without either jeopardizing wildlife or themselves, bearing in mind that house cats, unlike feral cats, tend to be easy pickings for coyotes, bobcats, foxes, and fishers.
Feral cats learn very early, from their mothers, to stick to a nocturnal existence, avoiding the scent of coyotes, bobcats, foxes, and fishers, and incidentally also maximizing their results from hunting by focusing on rodents and sick or injured birds who are still on the ground after dark, as opposed to wasting immense amounts of energy in mostly failed attempts to hunt birds by day.
ANIMALS 24-7 endorses the neuter/return approach to feral cat population control, because it works, and where practiced for significant lengths of time, has helped the recovery of wild mouse and rat predators, including hawks, owls, eagles, and the fore-mentioned foxes, fishers, bobcats and coyotes.
However, these wild mouse and rat predators are not always as well-adapted as feral cats to survival in particular urban and suburban habitats, and tend to be less well accepted by humans. Thus, regardless of the success of neuter/return in reducing the numbers of free-roaming cats, especially those who have been fed regularly by humans to the extent of becoming quasi-pets, there remains a viable niche for bona fide feral cats, who want and need nothing from humans except to be left alone.
Excellent article. I stopped using bird feeders years ago. Our resident city falcons would often swoop down and catch birds and not necessarily the sick or elderly. They were kept in breeding boxes built by the city mainly to control the pigeon population. The amount of bird feces at bird feeders can get quite large and many never bother to clean it up or disinfect. I also worry about toxoplasmosis, which is not so much a threat to the birds but potentially to cats who catch and eat the birds, and also pass toxoplasmosis on to humans. Usually toxoplasmosis is not a concern for those with a healthy immune system, but for those with compromised immune systems, whether feline or human, it has devastating effects. I have watched several people die from toxoplasmosis and it robbed them of their mental capacities well before death. If I am going to feed birds I do it in a park-like area and spread the food in a wide range so the birds are scattered. I try not to repeatedly use the same area.
While cats have been blamed for spreading toxoplasmosis for nearly 60 years now, the disease appears to have been unknown among cats until the advent of canned cat foods based primarily on fish. This and much other circumstantial evidence points toward an as yet unidentified marine host for toxoplasmosis. Details: Mystery marine toxo host kills sea mammals; cats wrongly blamed.
Should we not feed birds? Needless to say, I don’t want to unintentionally cause harm to wild birds. I have a small feeder that I clean with a bleach solution and let air dry when it’s empty. I don’t get huge flocks, in fact, I seem to have the same “crew” on a daily basis (none are pine siskins.) It does seem to help them find food more easily, at least in winter when snow is covering everything. I have not noticed any sick or dead birds.
ANIMALS 24-7 recommends feeding birds only in moderation, only from clean feeders, and as seasonally appropriate.
“In moderation” means not putting out more food in any one yard than the species attracted would normally find at a natural feeding source at the same time of year. Bird-feeding tends to become problematic when feeders attract birds in greater numbers than usually feed together in the wild, and/or keep birds in a habitat after they would otherwise migrate.