11 December 2006

Where do all the dead birds go?

In each issue, the British science magazine the New Scientist publishes questions submitted by its readers along with answers, also provided by readers, to previously published questions. I have posted my own answers to a couple of those questions here and here. Unless I missed it, the New Scientist still hasn't published an answer to the tripe question.

In the 25 Nov-1 Dec issue (No. 2579), a reader asked: "There are billions of birds worldwide, so why is it that you rarely, if ever, see a dead one?"

Well, I have seen many dead birds. In fact, I had a series of posts on the “afterlife” of one gray catbird (here, here and here). Once, I even found by the side of a busy road a large dead hawk that had apparently been struck by a vehicle. One summer several years ago, I explored a small Mediterranean island where gulls nested and where there were tens of dead juvenile gulls.

But, yes, one would think that with all those birds flying around, the dead ones would be coming down like rain. The reason why we don't see more dead birds is that dead birds, and in general all dead animals, get eaten very quickly. This is especially true in neighborhoods near forests. We have had our garbage can raided by raccoons and opossums on probably more occasions than we are aware of. With such scavengers prowling the neighborhoods nightly, the sun would never rise on a dead bird on a suburban yard.

For the same reason, one's chances of encountering a dead bird is even less in the woods. The only dead animals I have encountered in the woods were deer. They take longer to disappear, because they are so much larger than any other animal in forests around here. Incidentally, deer carcasses are more common alongside roads than in forests, because the scavengers have less access to them outside the forests.

Also, many birds are migratory. Many of those that die while flying at high altitudes may fall onto mountain tops or into oceans or forests.


Anonymous said...

I read a book in which it is written that jays (and many) sensed their time and moved to cracks,or other secure places.

To me it is evident that the rate of birds dying off-ground is much scarcer.

In Aladağlar, in S Turkey, ca 80 pelicans are found frozen at ultimate heights of the range.


Snail said...

Talk about synchronicity! I've just starting writing a post on this very subject and wandered over to Snail's Tales for a bit of a break. (And I haven't seen New Scientist for ages, so I can't blame that.)

Roger B. said...

Before they covered the building with nets, thousands of starlings used to roost on Sheffield town hall (giving rise to the nickname 'Starlingrad').

I'm told that foxes could regularly be seen patrolling the street below, cleaning up the birds which 'fell off the perch' during the night.

arshad said...

Liked your post !

John said...

Carcasses disappear pretty quickly in the city, too. We have rats, cats, raccoons, and crows; if they don't get them, the sanitation crews will. Even so I have seen plenty of dead birds, both large and small. Just the other day I saw a flattened ex-pigeon.

A lot of smaller birds may fall into bushes and thickets where they are not easily noticeable except by scavengers. Many weak birds are probably subject to predation before dying of disease or old age.

Nuthatch said...

I'd also add that if a bird is injured or sick, they are so vulnerable to predators that they usually retreat to heavy cover, and so die out of the way of most humans.

Most people, I think, are just not tuned into this kind of thing. When West Nile virus arrived in our region and was getting tons of press, people found all kinds of dead birds that were not victims of the virus - they were just cued into them by all the publicity.

Anonymous said...

Another note: many dies crashing to (reflecting) window glasses, either unseen or accepted as a conspecific male rival.

By the way, there is also a paper in Deinsea about a crash victim mallard getting attention by an alive male (single report of such a case). Animals and their attitudes to death are quite varying.


Neil said...

I agree that the premise is a bit off, I counted about half a dozen road-killed owls on a recent 200 mile interstate trip.

All the mechanisms mentioned above seem pretty applicable.

Another mechanism for the apparent disparity: the reason we notice the abundance of living birds is that they move around through the air, often congregate in large numbers and are rather conspicuous.

Of course, dead birds don't fly or flock and are harder to notice. This would seem to explain why no-one seems to be puzzled by the fact that they don't see more dead mice/insects/lizards or of other equally abundant but less noticable fare we share habitat with.

Rudko said...

Please never throw your apple cores or banana peels or any other edible foods out the car windows, it leads to many dead raptors.

I used to think throwing edibles out the car window was fine, not really littering since something would eat it. However, something does it, mice, which in turn brings the raptors, owls, hawks, etc. which often are killed by autos when they swoop down to take the mice.


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