Monday, March 21, 2016

Denialism about cats and bird kills

Pacific Standard has an interesting article about how California quail may have disappeared from the semi-wild areas of San Francisco. As both the state bird of California and the official city bird of San Francisco, that's a shame - they're a fun bird to watch.

The truth is they're hardly an endangered bird, so it's not a gigantic loss to biodiversity when they disappear in San Francisco. Still I'd much rather see natural components of environments survive, including in built-up urban areas.

What struck me about the PS article though was the role of cat advocates at the San Francisco Society for Prevention of Cruelty to Animals in preventing real actions to help the birds. Outdoor cats are huge killers of birds, probably hundreds of millions of birds annually in the US, but good luck getting many cat advocates to admit this. The people who feed feral cats drive the numbers even higher, and again they'll just dispute any science that gets in the way of what they want to believe. And in this (admittedly narrow) political area of trying to ban feeding and permanently remove feral cats, they're quite powerful.

Many people have tried to identify denialism that's primarily found on the left side of the spectrum. Vaccine denialism and ridiculous health claims about GMOs find a lot of the same beliefs on the right side of the spectrum. I don't know of any attempts to measure the cat advocates, but I imagine it's possible that this type of denialism may be found predominantly on the left.

I think some animal rights types may also indulge in related denialism, arguing that animal use in medical experiments is never useful, rather than arguing that they're overused.


Relatedly, if politics keeps feral cat colonies around, then one new option may be to give male cats vasectomies instead of neutering them - when they mate, the females enter a 45-day "pseudo-pregnancy," lowering lifetime fertility. These sterile-but-non-neutered males also tend to drive away other adult male cats that would create litters.

47 comments:

Fernando Leanme said...

California is indeed a very rich country. I have to confess that, when I was a teenager in Cuba, I participated in the movement to eat all the wild pigeons we could catch. One day, my friend Lenin suggested we eat a cat which had been partially run over by a bus. I guess you could say the end result of communism turned us into equal opportunity urban hunter-scavengers.

Harry Twinotter said...

I am inclined to think loss of habitat is more important than feral cats. Birds etc do know how to cope with predators.

Someone needs to do a study and try to get to the truth of the matter.

thelostcityofcarcosa.com said...

Shirley shome mishtake ?
I thought it was all the windmills (sic) that chopped up all the birds !?
That's the deniers' tone troll message.

Sarcasm aside, as servant/owner of two cats they are natural predators and owners should be under no illusions that they're going to bring home their kills which is a visceral reminder of their natural instincts. I have a mouse to remove from my front door mat.

There are too many cats and they should be sterilised, and that goes for feral cats as well. I got my two reprobates from a charity that inisits all cats are sterilised before being adopted. Fortunately the most prolific hunter goes for the rodents, and rabbits, not the birds

Mal Adapted said...

I'm a life-long keeper of cats, and since about 1990 all of mine (all shelter adoptees) have not only been spayed/neutered but kept indoors. Aside from the biodiversity costs of their predation on local small-vertebrate fauna, there's the risk of predation on the cats themselves, by (where I've lived in that time) coyotes and bobcats.

I take every opportunity to exhort my fellow cat-lovers: if you love your cats, keep them indoors, and be a savior of small wild creatures too.

Aaron said...

In wilderness areas, there are more bird predators, ranging from hawks and falcons to skunks and snakes that help control bird populations.

Birds can carry some nasty diseases directly, and often transport ticks that can transmit Lyme and other diseases. Anywhere there are migratory birds, there are likely ticks carrying Borrelia and /or other infections. Borrelia is a serious, and largely undiagnosed health issue.

Over all, unlimited numbers of birds are not a good thing. On the other hand, I do not think much of our bird population control consisting of windmills, glass office buildings, and cats.

jrkrideau said...

@Harry Twinotter

Birds etc do know how to cope with predators.
Don't forget that cats are an invasive species, not native to the Americas.

They seem to a real scourge in Australia.

Brian said...

Harry - no question that habitat loss is a far more important problem than feral and outdoor cats. The cats just make problems worse.

I probably shouldn't have ignored cats' effects on land vertebrates. In the case of house mice and the occasional rat, good riddance, but other rodents and lizards would be nice to have around more.

Aaron - I haven't heard of small birds that cats would hunt as being human disease vectors.

Howard said...

City people problems. In the Santa Cruz Mountains, the big cats remove the scourge of the feral and outdoor cats. Everytime a flat-lander moves into the neighborhood, they end up posting "missing cat" posters within a week or two. Perhaps the mountain lion and bobcats should be reintroduced into Golden Gate Park to return a semblance of natural depredation of feral cats and lounging druggies.

In any event, it's never wise to argue with or look into the eyes of a cat-lady.

Jim Eager said...

I will readily admit that my neutered tom takes the occasional bird, mainly ground feeding junkos and Eurasian sparrows (like the cat, a non-native species), and even the odd cardinal, but he also takes the rats (another alien) that like to burrow under my neighbour's composter, thus keeping them from gnawing their way under my mud room in the winter. With the latter he's doing the job that he was domesticated for, thanks very much, and I will keep letting him outside to do that job.

Dan Pangburn said...

"You can deny reality but you cannot deny the consequences of denying reality" Ayn Rand

8c7793aa-15b2-11e5-898a-67ca934bd1df said...

Why are you quoting a dead nutjob welfare case?

Mal Adapted said...

The title of this post is "Denialism about cats and bird kills", and sure enough we get a couple of comments from deniers:

"I am inclined to think loss of habitat is more important than feral cats. Birds etc do know how to cope with predators."

As if only one threat to bird populations could be important, or predation by cats is OK as long as there are other bird predators.

"I will readily admit that my neutered tom takes the occasional bird, mainly ground feeding junkos and Eurasian sparrows (like the cat, a non-native species), and even the odd cardinal, but he also takes the rats (another alien) that like to burrow under my neighbour's composter, thus keeping them from gnawing their way under my mud room in the winter. With the latter he's doing the job that he was domesticated for, thanks very much, and I will keep letting him outside to do that job. "

As if the only way to keep rats out of your mudroom is by letting your cat kill birds, or as long as the cat preys on introduced bird species it's OK if he preys on native species too. Don't thank me, you're not welcome!

Russell Seitz said...

There goes the National Debt !

Barton Paul Levenson said...

I LOVE ALL THE LITTLE KITTIES EVERYWHERE IN THE WHOLE BIG, WIDE WORLD!!!

Harry Twinotter said...

Mal Adapted.

I am surprised to see you resorting to ad homs and straw men.

Russell Seitz said...

Mal should re up in the Peace Corps if he can get a Cameroon posting .

There he will encounter the Fang, whose fondness for cat-based pepper pot soup led to conflicted views of cultural relativism among cat owning corpspersons in decades past.

Nigel Franks said...

It's not practical to eliminate feral cat colonies permanently. They get replaced by new cats in next to no time, not only by other feral cats taking over the area, but also by freshly abandoned cats.

The one policy that seems to have a measure of success is capture, neuter and release. But the big problem is irresponsible owners who don't sterilise their cats and abandon the unwanted offspring.

Mal Adapted said...

Harry Twinotter: "Mal Adapted. I am surprised to see you resorting to ad homs and straw men."

Harry, deniers make similar arguments, whatever they are denying. Perhaps you aren't a cats-and-bird-kills denier, but saying "I am inclined to think loss of habitat is more important than feral cats. Birds etc do know how to cope with predators" sure makes you sound like one.

Jim Eager said...

Sorry Mal, but I'm not denying anything: my one adopted, neutered, non-feral cat does indeed kill birds. That's unfortunate and I don't at all like it, seeing as I am an active birder, but I have a rat problem, thanks to my neighbour's refusal, to deal with it at the source. I can't trespass and dig up the rat burrow, nor can I set traps under his porch where the rats gnaw their way into my mudroom and basement. And using rat poison has serious negative consequences: have you ever had to tear down a drywall ceiling to remove the stinking carcass of a dead rat? Instead my cat deals with the rats, outside, plus he's great company when he's indoors. Sorry for the birds, but he works better than the other methods I've already tried or can't legally try.

EliRabett said...

FWIW, rats also kill birds, or at least eat their eggs, which is a huge problem on south pacific islands where neither rats nor cats were native

http://www.livescience.com/8858-island-rat-extermination-planned-save-endangered-birds.html

Brian said...

Nigel, it's quite possible to deal with feral cat colonies - trap them and don't return them, and fine the people that feed the cats. And heavily fine the people that abandon cats if you catch them.

WhiteBeard said...

The name is retained for the Island group, however.

http://www.adn.com/article/20160115/birds-are-returning-rodent-free-island-formerly-known-rat

WhiteBeard

cRR Kampen said...

Stats on cats & bird population trends, please.
I know - the latter are not offered readily by the birdloving cat haters, I wonder not why.
Cats do kill birds, but they apparently don't wipe them out into extinction.
So this debate can be held yearly for a looong time as it has been.

Mal Adapted said...

cRR Kampen: "Stats on cats & bird population trends, please. I know - the latter are not offered readily by the birdloving cat haters, I wonder not why. Cats do kill birds, but they apparently don't wipe them out into extinction."

Good grief, more denialism. I know better than to get sucked into the "citation needed" game with AGW-deniers, but as I'm a cat- as well as a bird-lover, I'll take your bait, this time only. A quick search on Google scholar turned up:

Loss, et al. 2013, The impact of free-ranging domestic cats on wildlife of the United States, Nature Communications 4, Article number: 1396. From the abstract:

"Here we conduct a systematic review and quantitatively estimate mortality caused by cats in the United States. We estimate that free-ranging domestic cats kill 1.3–4.0 billion birds and 6.3–22.3 billion mammals annually."

and:

Medina et al. 2011, A global review of the impacts of invasive cats on island endangered vertebrates, Global Change Biology 17, pp 3503–3510. From the abstract:

"Feral cats on islands are responsible for at least 14% global bird, mammal, and reptile extinctions and are the principal threat to almost 8% of critically endangered birds, mammals, and reptiles."

cRR Kampen: "So this debate can be held yearly for a looong time as it has been."

Yep, just like the manufactured AGW "debate". Look, nobody's perfect, least of all me. I'm guilty of countless large and small crimes against the biosphere like everybody else. But denial is denial, and it's just not respectable, whatever is being denied. The commenters evincing denial here aren't AGW-deniers, by their previous comments. What's different about cats and birds?

cRR Kampen said...

"We estimate that free-ranging domestic cats kill 1.3–4.0 billion birds"

Not relevant. Are those bird species going extinct in no time flat? No, they are not.

"Feral cats on islands are responsible for at least 14% global bird, mammal, and reptile extinctions and are the principal threat to almost 8% of critically endangered birds, mammals, and reptiles."

Not relevant, this is a cherry pick. Introducing new species somewhere often does tend to change the entire ecological make-up.

I repeat: stats on cat & bird population trends, please.
It is easy enough to see the cause behind the global temp and [CO2] increase correlation.
Now I want to see graphs of feral incline vs bird decline.

This is de first question one poses when someone links two phenomena. SHOW the link. It is always omitted in this specific debate and like I said, I know why.

cRR Kampen said...

Damn... "A global review of the impacts of invasive cats on island endangered vertebrates" then read the abstract and it's only about islands.

This looks like the second time I'm experiencing people who have a good, scientific conception on one subject (e.g. climate change) but lose it completely on another.

Barton Paul Levenson said...

This source is not peer-reviewed, but is by a wildlife biologist:

http://www.amnh.org/ology/features/askascientist/question16.php

She estimates 200-400 billion birds exist at present, and the total is definitely declining. If cats are really killing 1.3-4.0 billion birds per year, that's enough to significantly affect the death rate.

I think we can agree that, even if the major cause for bird decline is habitat destruction, it wouldn't hurt to spay or neuter both domestic and feral cats. This is not cat hatred; it's good for the cats as well, since they are less likely to overpopulate and starve that way--plus, in the wild, kittens are "the lunchables" for larger predators (dogs and raptors, mostly), as one biologist I know puts it.

Barton Paul Levenson said...

Here's the peer-reviewed citation for that number:

Gaston KJ and Blackburn TM 1997. How many birds are there? Biodiversity and Conservation 6, 615-625.

http://link.springer.com/article/10.1023%2FA%3A1018341530497#page-1

Russell Seitz said...

People eat 1.5 trillion chicken eggs a year, and a single sushi restaurant takes a trillion sea urchin eggs out of circulation annually:

How many years before we can throw away our reef shoes and the roosters shut up ?

Mal Adapted said...

cRR Kampen, you are modeling cat-and-bird-kill denialism so skillfully, I'm beginning to think I'm being poed. If so, congratulations. You've learned well by studying AGW-deniers.

cRR Kampen said...

Mal Adapted, please cut it out and come up with statistics showing for the US and/or Europe and/or Asia the following:
- Where feral presence increases, bird species vulnerable to them deplete into extinction.

What you did not, I did for Holland, because we got some numbers. At first sight they would seem to corroborate your hypothesis. Because over the cause of past 20 years, a number of bird species at first declined in population, then rose again while the cat population showed a (weaker) opposite trend + trend reversal.
The problem is, the birds affected are no cat's prey. Their decline is caused by changes in agriculture.
The titmouse, a dweller of sloppy weeded/shrubbed areas in cities, declined strongly during the end of last century against no trend in cats then; after which this population very strongly regained. A link with city planning trends is suggested on a Dutch bird watcher's site (which never mentions cats btw).
The northern provinces of Holland have most birds and species. It is also the region with most cats, including many strays and farm cats.

A remark by BPL - "If cats are really killing 1.3-4.0 billion birds per year, that's enough to significantly affect the death rate."

You can't state that just like that. You need to correlate trends in feral presence AND bird kills AND bird decline. Yes: three things, and if you find correlation you will STILL have to show causation.

Also, a yearly kill rate of birds by cats of less then 1% will most decidely NOT affect bird populations at all. It is a comparably tiny cause of death.
As to the rest of BPL's post, I simply agree.

Now. Come up with the numbers. Pretend its AGW if that is how can come back to a more scientific way of thinking about this.

cRR Kampen said...

BPL's link also does not mention cats. Not even those prowling the rain forests (if we are to believe the hypothesis the rain forests must be teeming with cats...).
It looks like actual bird specialists and -watchers don't care too much about cats.

There is something fundamentally wrong with this debate. I suspect some fact evading cat hate around on this one. The debate is generally conducted by many who simply know nothing of cats, birds and their relations. This is why they cannot supply the numbers I'm asking.
This would explain some very strange responses I got on my calls for some science on the subject.

Barton Paul Levenson said...

We need to know:

The annual birth rates of birds.
The annual death rates of birds.
The total population of birds.
The contribution of each factor (fatal disease, senescence, predation, starvation due to habitat loss, fatal accident from human encroachment, evil wind turbines, etc.) to the death rate.

Then we can do ANOVA.

Time series statistics on all of the above would help. Ditto the birth, death, etc. rate for domestic and feral cats. We've got two figures so far: world bird population 2-400 billion, and bird kills from cats 1.3-4.0 billion. Help me fill in the rest.

cRR Kampen said...

Exactly, BPL.

And for saying this, I got dumped into the climate revisionists' bucket. Fucking brilliant. I hope Mal Adapted can reconstruct how that worked. That cognitive process could help us gauge climate revisionism so much the better.

My guess is - it's all about habitat.

cRR Kampen said...

Please be nice to me.
We lost Johan Cruijff today :(

Barton Paul Levenson said...

Here's what I've got so far.



Global Figures:

bird population 300 ± 100 G [Gaston & Blackburn 1997.]
cat population 600 M [McLamb 2013]
feral: 100+ M [McLamb 2013] as 60+ M USA, 12 M Australia, 3 M Canada, 1 M UK
domestic cats kill 1-34 birds/y, feral 46 [McLamb 2013], mean 36 in Canada
bird death rate: 50%/year???



Regional Figures:

Tropical ... bird loss 144.4 M/y [Remsen 1995]
Mediterranean countries ... 1 G migratory birds to hunting/trapping [Magnin 1991]
USA... 97.6-975.6 M window strikes/yr [Klem 1990]
1.25 M communications tower strikes/yr [Banks 1979]
57.2 M road kills/yr [Banks 1979]
80-319|638 M predation by domestic cats/yr [Winkler et al. 1991, Walsberg 1994]

http://www.mapsofworld.com/world-top-ten/countries-with-most-pet-cat-population.html
Top Ten Countries With Most Pet Cat Population, Maps of World, accessed 3/24/2016

USA 76,430,000
China 53,100,000
Russia 12,700,000
Brazil 12,466,000
France 9,600,000
Italy 9,400,000
UK 7,700,000
Ukraine 7,350,000
Japan 7,300,000
Germany 7,700,000

sum 203,746,000



Banks, RC 1979. Human related mortality in birds in the United States. U.S. Fish and Wildlife Service Special Scientific Report. Wildlife No. 215.

Gaston KJ, Blackburn TM 1997. How many birds are there? Biodiversity and Conservation 6, 615-625. http://link.springer.com/article/10.1023%2FA%3A1018341530497#page-1, accessed 3/24/2016.

Klem Jr. D 1990. Collisions between birds and windows: mortality and prevention. J. Field. Ornithol. 61, 120-8.

Magnin G 1991. Hunting and persecution of migratory birds in the Mediterranean region. In Conserving Migratory Birds (T. SalatheÂ, ed.), pp. 63-75. Cambridge: International Council for Bird Preservation

McLamb E 2013. Born in the Streets: The Global Impact of Feral Cats. http://www.ecology.com/2013/08/27/global-impact-feral-cats/, accessed 3/24/2016.

Remsen Jr. JV 1995. The importance of continued collecting of bird specimens to ornithology and bird conservation. Bird Conserv. Int. 5, 145-180.

Walsberg GE 1994. The use of wild birds in research. Condor 96, 1119-1120.

Winkler K, Fall BA, Klicka JT, Parmelee DF, Tordoff HB 1991. The importance of avian collections and the need for continued collecting. Loon 63, 238-46.



I am continuing to collect data from the internet. If anyone can help...

cRR Kampen said...

I think there is some burden of providing evidence on Eli and e.g. Mal Adapted.

On a somewhat related subject, touching bird populations' demise by the introduction of cats to a.o. islands - species travel, more so since humans travel, and when something new becomes succesful in some ecosystem it often becomes so devastatingly, to the extent of plagues.
- The exospecies of gray squirrels have all but replaced the home species of red squirrels in Holland.
- The exospecies of American red river yabby (or what those sweetwater lobsters are called) has extinguished to the count of one pond housing a few thousand the European/Dutch river species.
In this case, both processes evolved not from direct predating but thru the introduction of diseases the immigrants are immune to but the locals aren't (yet).
The general theme is - you introduce new species, if they thrive they will cause some, more, or less disaster. So with cats on islands that used to be for the birds.

Incidentally, they had this Rabbit Fence down under. Can we have cat fences?

Jim Eager said...

Barton, in hard copy there is Bridget Stutchbury's Silence of the Songbirds and it's footnotes and references. Stutchbury is at York U in Toronto.

Mal Adapted said...

I'm still not convinced Heer Kampen is serious.

Brian's hypothesis, in the OP, was:

"Outdoor cats are huge killers of birds, probably hundreds of millions of birds annually in the US".

When Heer Kampen demanded numbers, BPL and I provided links to publications containing numbers that support the hypothesis (1.3–4.0 billion birds may not qualify as "huge" in his estimation, but it does in mine). Heer Kampen asserted "Cats do kill birds, but they apparently don't wipe them out into extinction." When I linked to a report linking feral cats to extinction of island endemic species, he responded: "Damn... 'A global review of the impacts of invasive cats on island endangered vertebrates' then read the abstract and it's only about islands."

Uhmm, he didn't need to read the abstract to find out it's only about islands, the title should have told him. That when I wondered if he was being serious, but then he said: "Mal Adapted, please cut it out", and moved the goalposts:

"come up with statistics showing for the US and/or Europe and/or Asia the following:
- Where feral presence increases, bird species vulnerable to them deplete into extinction."

Well, that wasn't the hypothesis Brian proposed, was it?

Heer Kampen then said: "There is something fundamentally wrong with this debate. I suspect some fact evading cat hate around on this one. The debate is generally conducted by many who simply know nothing of cats, birds and their relations."

This is what's called "poisoning the well". It's all the more fallacious because I've made it clear I'm a cat-lover, and that after growing up with them, I've been adopting shelter cats to be my companions for the last 25 years. I think I know a little bit about them. As a student of evolution and ecology from childhood through two years in a doctoral program (when I found an easier way to make a living), I also know a little bit about predator-prey population dynamics.

Heer Kampen: "My guess is - it's all about habitat."

This is an indicator of the Dunning-Kruger effect. Trained ecologists don't have to guess, they know that mortality factors have additive effects on species populations. A species with stable population numbers under the sum of existing mortality factors will often decline if mortality increases from any cause. It would be astonishing if the introduction of an efficient new predator did not cause extinction of the most vulnerable species, especially island endemics. Habitat loss nearly always increases mortality too, but habitat loss combined with introduced predators just means faster population decline than either by itself.

Heer Kampen says: "I think there is some burden of providing evidence on Eli and e.g. Mal Adapted."

Nuh-uh. The peer-reviewed evidence supporting Brian's original hypothesis has been provided. The burden is now on him to challenge it, preferably by writing up your criticisms and submitting them to the same journals.

"And for [moving the goalposts], I got dumped into the climate revisionists' bucket. Fucking brilliant."

Perhaps Heer Kampen can reconstruct how that worked. What's puzzling to me is that by his comments on RR and elsewhere, Heer Kampen is not a climate revisionist. Nevertheless, on the issue of cat predation on birds, he's modeling the paradigmatic science denier convincingly.

With that, I'm done. It's OK with me if Heer Kampen declares victory, it's what I expect a denier to do.

Jim Eager said...

Didn't have time to check my copy of Stutchbury's Silence of the Songbirds before now. Stutchbury mainly focuses on habitat loss and fragmation, which in breeding terms is as good as loss. She only discusses domestic and feral cat predation over three pages out of 226, and mentions three studies, none of them cited by title or researcher. One in southeastern Michigan estimated that domestic cats take on average one bird per week. The second study in Wichita, Kansas examined domestic cat feces and found bird remains in 10% of samples. A third study in rural Wisconsin estimated 8 to 217 million cat predations per year, with free-ranging cat populations as high as 40 per square km in the study area. She puts total US cat population at over 75 million.

Frankly an estimate range of 8 to 217 million - a factor of over 27 - tells me the researchers have no idea what the real figure is. Never the less cats are clearly a serious predator of birds. Feral cats depend on kills for more if not most of their diet, but there are certainly more non-feral but free-ranging cats than feral. Yet Stutchbury spends more space discussing parasitic predation by cowbirds. Far more. And most of the book discussing habitat loss. I'm sure there's a reason for that.

cRR Kampen said...

So Mal Adapted, following Brian, has discovered that cats kill birds.
Wow.
How relevant is this piece of knowledge, that was rather general except for some?
Was this all this was about? That cats kill birds?
I cannot fathom how anyone could accuse anyone of denying this.

"Outdoor cats are huge killers of birds, probably hundreds of millions of birds annually in the US".

Yeah, so what. Cats, you know.


cRR Kampen said...

And no, I am not a climate revisionist.
I am, in fact, the sole inventor of this phrase.

Barton Paul Levenson said...

More from the Loss et al. 2013 study:

Loss SR, Will T, Marra PP 2013. The impact of free-ranging domestic cats on wildlife of the United States. Nature Communications 4, Article number: 1396.

Abstract: Anthropogenic threats, such as collisions with man-made structures, vehicles, poisoning and predation by domestic pets, combine to kill billions of wildlife annually. Free-ranging domestic cats have been introduced globally and have contributed to multiple wildlife extinctions on islands. The magnitude of mortality they cause in mainland areas remains speculative, with large-scale estimates based on non-systematic analyses and little consideration of scientific data. Here we conduct a systematic review and quantitatively estimate mortality caused by cats in the United States. We estimate that free-ranging domestic cats kill 1.3–4.0 billion birds and 6.3–22.3 billion mammals annually. Un-owned cats, as opposed to owned pets, cause the majority of this mortality. Our findings suggest that free-ranging cats cause substantially greater wildlife mortality than previously thought and are likely the single greatest source of anthropogenic mortality for US birds and mammals. Scientifically sound conservation and policy intervention is needed to reduce this impact.

...with ~69% of this mortality caused by un-owned cats. The predation estimate for un-owned cats was higher primarily due to predation rates by this group averaging three times greater than rates for owned cats.

USA: 84 +- 2.5 M owned, 50-80% hunting
60-100 M unowned, 80-100% hunting

Fraction of mortality for different bird species ranged from 0.160 to 0.001; no overall estimate was given. Note this means 84.0-99.9% of bird deaths are from other causes. This does not necessarily mean cat predation is negligible; consider the example of the bathtub with the faucet on and a hole in the side. A small difference in input can make a large difference over time, as with CO2.

Barton Paul Levenson said...

Hounsome M 2003. Lifespan of Birds--How long does a bird live? http://www.countrysideinfo.co.uk/bird_lifespan.htm, accessed 3/25/2016

Banding studies show 60% mortality of adult robins/y
survival = 1 - mortality
life expectancy = -1 / ln(survival)
So 1.1 y for adult robins.

"Most of our common small birds have similar survival rates and life expectancies. Adult survival rates are usually between 0.4 and 0.6 with first-year survival rates often being between 0.1 and 0.2 - so roughly a half of all the adult birds and nearly ALL the baby birds you see will be dead in a years time. It’s a sad thought, but this has to happen if the population is to remain roughly constant."



This is about the most useful data I've gotten so far. If we assume 1) global bird population is 300 billion, and the death rate is 50% per year, then 150 billion birds die every year. If cats kill 1.3-4.0 billion, this is 0.089-2.7% of the global death rate. This is small but perhaps non-trivial. Thus it would likely help to restrain cat predation, so trap-neuter-return for feral cats, and restricting outside hunting by pet cats, are probably good policy goals.

cRR Kampen said...

"This does not necessarily mean cat predation is negligible.." - certainly not. Just as the human contribution to the globe's CO2 production, while only comprising a couple percent, is far from negligable. In this case, its effects are far from negligable too, as we all know here.
Whether the hole or the faucet is the larger still remains to be seen wrt cats and birds.

But actually I have grown quite content with this highly informative topic and discussion. Cats kills birds, well ibd.

Brian said...

I'll add that cats don't need to be causing extinctions to be a problem. I doubt they are except on islands and in rare cases. They are still reducing the population density and diversity of wildlife, as seen in the original link at this post.

Also they can be bad without making things worse. I doubt there is a negative trend in a typical suburban tract, but the point is there could be significantly more birds, lizards, frogs etc. if there weren't so many cats hunting.

One idea that might help - now that we can figure out which cats hunt and which ones don't, it should be possible to breed cats for the non-hunting trait.

Because I like repeating myself, I'll just say again - habitat loss is the big problem. Also trap and neuter is fine, but return is the problem (and even more so, the constant feeding that people do).

cRR Kampen said...

".. but the point is there could be significantly more birds, lizards, frogs etc. if there weren't so many cats hunting."

True, this could well be.
It looks hard to verify against other environmental pressures, plus the fact that cats have been around in our growing societies for centuries so the question becomes whether they have or have not simply become part of the humanity-made ecological systems (as they are often not or not yet on islands).