Dead baby birds: why here, why now?


Here is a mystery I'd really like to know the answer to. On the way to school this morning, Will discovered a dead baby bird. Here it is: the photo (which I took on my phone) is atrocious, so there's little point in showing it at larger size. Clearly, this is an altricial, nidicolous passerine chick, probably of a Blackbird Turdus merula. The question is: how does an altricial nestling like this - barely able to walk in its own nest, least of all out of it - get to be dead in the middle of the pavement? No, it didn't fall out of its nest, because there were no overhanging trees or bushes where a nest might be.

The idea that a predator - like a corvid or domestic cat - pulled it out of the nest and then dropped it is, of course, possible, and there are certainly magpies, carrion crows and cats in the area. However, over the years I've seen dead passerine nestlings out in the open - on pavements, roads and such - on so many occasions that I've wondered if something else might be going on. Surely predators can't be dropping their spoils on such regular occasions? We know that cuckoldry is common in passerines like starlings, and that some species (like House sparrows Passer domesticus and Barn swallows Hirundo rustica) sometimes practise infanticide (e.g., Møller 1988, Hansson et al. 1997, Veiga 1990, 2003, 2004). Incidentally, while typically associated with males, infanticide is commonly practised by females in some species, like the House sparrow, and also in those most evil of mammals, rodents and primates. In species with polygynous males, females might practise infanticide so that the male ends up allocating more of his time towards the infanticidal individual's brood. Clever.

But perhaps most interesting is the fact that some passerines destroy the eggs, nestlings and even nests of other birds: this is mostly an intraspecific behaviour, but - in cavity-nesting wrens, at least - members of some species will even destroy the families and nests of other species (Belles-Isles & Picman 1986 and references within). It's generally thought that this behaviour reduces competition for resources, and that makes sense. How do these passerines kill the eggs and nestlings of other birds? Eggs are broken open by pecking, but I'm not sure what's done with nestlings. Are they smacked on the head, or just pulled out of the nest? Once this happens, the nestlings would die quickly from exposure. And is this sort of behaviour more widespread in passerines than indicated by the literature? Might it occur intraspecifically within species like the Blackbird, for example? We already know that these birds are fiercely territorial and hence in constant competition with their neighbours, so it doesn't seem much of a stretch to imagine that the birds might kill the nestlings of their competitors if the chance arises. However, you'd think that this sort of thing would have been observed in such a well-studied species: if it is, I can't find a mention of it in the literature.

Incidentally, I did once keep and skeletonise a dead passerine nestling I found on the pavement. Unfortunately it's not with me here, but at Portsmouth University, so no photo.

Refs - -

Belles-Isles, J.-C. & Picman, J. 1986. House wren nest-destroying behaviour. The Condor 88, 190-193.

Hansson, B., Bensch, S. & Hasselquist, D. 1997. Infanticide in great reed warblers: secondary females destroy eggs of primary females. Animal Behaviour 54, 297-304.

Møller, A. P. 1988. Infanticidal and anti-infanticidal strategies in the swallow Hirundo rustica. Behavioural Ecology and Social Biology 22, 365-371.

Veiga, J. P. 1990. Infanticide by male and female house sparrows. Animal Behaviour 39, 496-502.

- . 2003. Infanticide by male house sparrows: gaining time or manipulating females? Proceedings of the Royal Society B 270 (Suppl 1), S87-S89.

- . 2004. Replacement female house sparrows regularly commit infanticide: gaining time or signaling status? Behavioral Ecology 15, 219-222.

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I would have assumed a parent would remove a dead chick from the nest in the same way they remove eggshells, to be dumped at some distance from the nest?

By DunkTheBiscuit (not verified) on 01 May 2009 #permalink

Given the extreme territoriality of some of these passerine species I wonder if human activity could be causing an increase in intraspecific and/or interspecific infanticide as appropriate habitat and prime territory become harder and harder to find.

Apparently, introduced house sparrows are very bad news for native songbirds in North America; adults will enter nestboxes occupied by other species of bird, and destroy the eggs and nestlings. If there is an adult bird inside the nestbox, then the sparrows will possibly kill the other bird, and might even build their nests on top of the carcass of the original occupant.

Yeah, this is documented in the Belles-Isles & Picman (1986) reference cited above. I had forgotten about removal of deceased young by the parents: that looks like a pretty viable answer.

This reminds me of the fact that, some weeks ago, I visited Blijdorp Zoo in Rotterdam (as I regularly do). The zoo has this large central pond with pavement and animal housing near it and no large trees to speak of.

Anyways, laying among its margin, surrounded by the pond's wildfowl lay a young dead heron (presumably a Blue Heron). It was still, fairly small (about half adult size) and naked except for retrices. Now, I assumed this poor fellow had been either chucked out of the nest, fallen or taken by a predator. The strange thing however, is that the nearest heron rookery is a few miles away. I've never seen any herons nesting in the zoo itself. At the time I was quite confused as to how the nestling had gotten there.

Could it have been taken out of the nest by another heron and then left to die near the pond? Are herons capable of carrying such a 'halfling' for such a distance? I must say the nestling was not very damaged; eventhough some gulls had started to peck at it. Any thoughts?

I did once keep and skeletonise a dead passerine nestling I found on the pavement.

Just how do you skeletonize juvenile animals? I once tried to skeletonize a baby turtle, but the skeleton broke into so many goddamned little pieces (because it was still growing) that I couldn't do anything with them. Of course, *I* couldn't do anything with them because I had absolutely no clue where each part should go... do you actually take the time to reconstruct every single bone?

Or maybe birds' bones just don't grow like turtle and mammal bones?

I used Black ants Lasius niger to deflesh the passerine: they aren't big enough or voracious enough to disarticulate the bones, and the whole skeleton was left intact and fully articulated. I'll publish a photo of the specimen when I get one.

I'm not a scientist, just an occasional reader, and know little about bird behaviour except what I witness in my suburban back garden. This year we seem to have about five blackbirds in competition for the food put out and the males (sometimes 3)have been extremely aggressive with mid-air noisy fights at times. I think you might have something in the 'murdering of babies to keep their food source' theory, Darren.

OR, I did see a large crow with a juvenile in its beak one year being harried by a brave parent blackbird. The fully feathered youngster was saved. In shock it rolled down my extension roof and scuttled away at speed into trees.

By Sandra Naish (not verified) on 01 May 2009 #permalink

My sister's dog used to find (live) baby starlings in the bushes all the time and carried them back to us. With no idea where the nest was, we'd have to leave them on the ground near a tree and hope for the best. I'm sure not all of them made it - perhaps the parents tried to carry it back to the nest and just couldn't manage?
I've known housecats to do something similar, since many of them kill prey more by accident than design. Possibly it played with the "toy" until it stopped moving and being interesting, then left it. Lord knows my cats leave their toys in bizarre places.
Obviously that doesn't account for all of them, but certainly some.

By Omphaloskepsis (not verified) on 01 May 2009 #permalink

A friend of mine living in rural Eastern Massachusetts had live naked baby swifts (Chaetura pelagica) fall down into her empty fireplace. Even though we knew exactly where the nest was, we could hardly replace them, so we just euthanized them.

I'm not saying it amounts to anything but it is interesting to take it from the other end.

What is special about pavement? In the picture it is dark but generally it is warmed by the sun.

What does warmth have to do with it? We are talking about The first of May so warmth might, depending on the latitude, be a precious thing. Warm days and cool nights are common.

Who or what benefits from this warmth?
If a chick were to fall or be pushed from its nest it might seek out the warmth as the temperature fall. Where it gets stepped on, run over or lunched.

If an animal wished to eat a chick but wasn't gifted with teeth suitable for tearing into it, or just liked its bird a bit softer, it might want the meat to age. A warm bit of pavement might serve to speed the process. Alligators commonly store their catch underwater to tenderize it.

Stories end up like this:
1)Chick falls out of nest and seeks warmth of pavement. 2)Animal places chick on pavement to speed aging.

3) Humans just aren't very observant so we notice dead chicks on flat surfaces but fail to observe the dead chicks in the grass or otherwise obscured by foliage.

This may be magnified by the lower level of biological clean up that goes on on hard surfaces. Places where crows, vultures and other large animals risk being run over if they try to feed. Which might mean the carcass stays relatively intact and easier to spot longer. This may run counter to #2.

Given recent posts and comments about bird fights, competition, etc., I thought you all might find this interesting.

Observed a pair of Western Scrub-jays Aphelocoma coerulescens fighting outside my office window in Olympia, Washington, today. I suspect it might have been over access to the bird feeder we have hung there. Tactics observed included beating with the wings, feather pulling, stabbing the opposing bird in the chest with the bill, and clamping the bill down on the opponent's foot. Two additional individuals (the mates of the birds involved in the fight?) repeatedly flew back and forth to the site of the battle, making a lot of noise. The loser apparently conceded by lying on his back with his wings outstretched.

A. coerulescens is a relatively recent immigrant to the Puget Sound region from Oregon and extreme southwest Washington. Based on personal observation, their population in the downtown Olympia area appears to have grown hugely over the last ten years or so; I wonder if competition for suitable nesting sites is increasing.

Perhaps the chick fell out of the nest and in an (obviously doomed) attempt to get back, it drug itself into the middle of the pavement and died of exhaustion?

By Pete Buchholz (not verified) on 01 May 2009 #permalink

Why did the chicken cross the road?
To beat the egg. Thus solving the riddle,
"Which came first, the chicken or the egg?".

No idea about blackbirds though, perhaps a well-fed over-active cat?

A bird at the stage shown in the photo would not have been able to crawl any sigificant distance, so despite some of the suggestions I can't belive it played any part in getting itself to the middle of the pavement.

When very young birds are found dead 'in the open' not near to any obvious nest I would suggest that a combination of removal of young that died 'of natural causes' by parents and being taken by domestic cats and dogs that are not hungry and therefore leave them uneaten, explain most instances.

I recall my brother's spaniel findng a blackbird nest in one of the hedges in my garden and killing the young without eating all of them, just dropping them some distance from the nest. It all happened to quickly for us to stop, and though I know spaniels can be good climbers I would not have thought he could have reached them in the hedge, but he did. After that I did wonder what proportion of the bird deaths blamed on cats and corvids actually are caused by domestic dogs.

By Mark Lees (not verified) on 02 May 2009 #permalink

I have no special idea. Removal of dead young by parents is possible.

Other may be that local cats treat baby birds as playthings. House cats are terrible creatures, apparently 1/3 of well fed house cats hunt and kill purely for pleasure. So, some can rob the nest but not eat chicks.

BTW - side topic.

House cat in Britain is very important but unstudied predator. When you count number of domestic cats and how much a cat must eat, it turns that cats are important ecologically. They eat more prey than eg. owls or most birds of prey, even if many cats don't hunt at all. But this animal is very poorly studied. There is a empty study area here. So, forget hypothetical escaped big cats, small cats in British countryside are worth studying for a zoologist.

In N. Am., we have a related species, Turdus migratorius, commonly called a Robin (not the UK species, of course), and it's not uncommon to find nestlings on the ground (I've seen it twice, once in a forest and once on the Alaska Highway [?!]). Apparently they fall out, and the parents continue to care for them. From your picture, I'd guess that this happened, and that the nesting wandered onto a paved section of road and either died of the cold (at night) or the heat (during the day).

A while back some bluetits set themselves up in a nest box in our garden. A magpie was showing a lot of interest but the nest was quite difficult to get at. Some time later we found six dead chicks on the ground under the box. Naturally we blamed the magpie, but couldn't understand why having gone to the trouble of pulling them out it hadn't eaten them ....

@previous users
This chick is clearly too young to survive outside the nest.

It is common that chicks of songbirds leave the nest 1-2 days before being able to fly, and parents tend them, but chicks are then feathered birds with only wing and tail feathers not fully grown.

Response to Jerzy on domestic cat predation: there are at least a few studies that look at the impact of domestic cats on wild fauna, and as you say all find that domestic cats have a significant impact, even on animals not typically considered much affected by cats (like bats: cats are responsible for more bat deaths than all other causes of mortality put together, and the annual 'bat catch' outnumbers the total populations of some British bat species). If you google 'domestic cat predation' you'll see what I mean. Here in Britain some of the most revealing studies have been...

Woods, M. 2001. What the cat brought in. BBC Wildlife 19 (2), 30-32.

- ., McDonald, R. A. & Harris, S. 2003. Predation of wildlife by domestic cats Felis catus in Great Britain. Mammal Review 33, 174-188.

Wierdly, I was talking with one of the Regents Park (London) gardeners today about the large number of dead baby birds that appear from this time of year into the summer (their smell, along with the similar scent of Sorbus bushes, often waylays you when taking a pleasant walk...)

Anyway, he said that most of the hedgerow passerines there are predated by Magpies or Grey Squirrels, and they often leave items when interrupted or when squabbles escalate into the kind of fights where the cause is forgotten. Either this, or the already mentioned parents removing fatalities, seems the most likely reason for an unconsumed dead 'un to be left on the tarmac.

Surprised squirrels were omitted from the suggested potential predators here, though - they're very destructive of native British fauna...

By David Callahan (not verified) on 02 May 2009 #permalink

Where I live, south of Austin, TX, the most common snake appears to be the rough green snake. These are a small, bright green, largely arborial snake. I've seen them in trees and bushes a number of times, and a couple of times on the ground in transit. I've also found two dead on the asphalt driveway a little distance from any trees or brush. Both were upside down and appeared uninjured, just dead.

On a small animal like a baby bird, you might do a clear and stain preparation. It is easy and cheap and produces an informative and attractive specimen. I should be able to give you a reference, but am having a senior moment and can only remember the first name of one of the authors.

By Jim Thomerson (not verified) on 02 May 2009 #permalink

David Callahan wrote...

Surprised squirrels were omitted from the suggested potential predators here, though - they're very destructive of native British fauna...

The bird was not found in an area surrounded by woodland where diverse wildlife occurs: it was at the side of a busy road, flanked only by suburban gardens. There are no grey squirrels in the area. As for the impact of squirrels on British birds, you should see the Tet Zoo article here.


But this animal is very poorly studied.

I don't know what your criteria for "poorly studied" are, but there have been a number of UK studies on domestic (i.e., not feral) cat predation. Apart from those mentioned by Darren, there are also, for example, Mead (1982), Churcher & Lawton (1987), Carss (1995), and Baker et al. (2005).


all [of those studies] find that domestic cats have a significant impact

True - and false.

True when it comes to rodents and other small terrestrial mammals: on their populations, domestic cats may indeed have a locally significant impact.

But (probably) false when it comes to birds - which is what we're talking about here. For birds, the actual hard evidence is much more equivocal. For example, Mead (1982) says (p. 186) that "there is no clear evidence of cats threatening to harm the overall population level of any particular [bird] species". Churcher & Lawton (1987) found that for only one bird species, the house sparrow Passer domesticus, was there any indication of a significant cat-caused negative impact on population size. Baker et al. (2005), on the other hand, suggest that cat predation may have a negative impact on house sparrow, dunnock Prunella modularis and robin Erithacus rubecula populations, but probably not on the populations of other British garden bird species.

Thus, it seems that the commonly held idea that domestic cats are extremely harmful to bird populations is, at least in most cases, rather less than entirely justified.

As for bats...

cats are responsible for more bat deaths than all other causes of mortality put together, and the annual 'bat catch' outnumbers the total populations of some British bat species

Darren, where does that information come from? In the Woods et al. (2003) paper that you cite*, relatively few bats are recorded as cat prey (30 to be precise: 22 unidentified bats, four unidentified pipistrelles, and four long-eared bats Plecotus auritus out of a total of 14,371 prey items).

* I don't have access to BBC Wildlife magazine, alas.


Baker, P.J., Bentley, A.J., Ansell, R.J. & Harris, S. 2005. Impact of predation by domestic cats Felis catus in an urban area. Mammal Review 35, 302-312.

Carss, D.N. 1995. Prey brought home by two domestic cats (Felis catus) in northern Scotland. Journal of Zoology, London 237, 678-686.

Churcher, P.B. & Lawton, J.H. 1987. Predation by domestic cats in an English village. Journal of Zoology, London 212, 439-455.

Mead, C.J. 1982. Ringed birds killed by cats. Mammal Review 12, 183-186.

When saying that cats have a significant impact, I meant on fauna as a while, not on birds specificaly (I was responding to Jerzy's comment that the house cat is indeed ecologically significant).

As for bats, my assertion came from Altringham (2003): citing a Mammal Society survey of 1997 in which cats were estimated (by extrapolation from a sample of 1000 cats) to kill a minimum of 230,000 British bats each year, he concluded 'If these 1,000 cats are typical, and there is no reason to believe they are not, cats kill more bats than all other natural predators combined. They are one of the biggest causes of bat mortality in Britain, perhaps the biggest' (p. 139). The number of bat deaths reported in the survey was a minimum because the survey only counted prey that cats brought into the house, and ignored what they ate or left outside.

Ref - -

Altringham, J. D. 2003. British Bats. HarperCollins, London.

my assertion came from Altringham (2003): citing a Mammal Society survey of 1997 in which cats were estimated (by extrapolation from a sample of 1000 cats) to kill a minimum of 230,000 British bats each year

Hmm. Give or take a few ten thousand, the numbers seem to add up (if one assumes that the total British cat population was about seven million in 1997). Is cat predation skewed towards those bat species that roost in buildings, as one might expect? And how reliable are British bat species population estimates?

(Sorry for going off-topic with these questions, but I don't have access to that book by Altringham either.)

Last year, I found a lot of baby birds outside our office. They were at least ten Carduelis chloris (verderon is the local name, a sparrow-like bird) and that never happened again. As our building is full of external holes ideal for nesting, I think it is possible some epidemic happened and parents pushed dead bodies outside.

That, and the fact that our workplace is an Evil place where living things come to die :)

The British domestic cat population is about 7.5 million. The bat species most affected are the pipistrelles and long-eared bats that roost in/close to human habitations, but other species are affected too. As for bat population estimates, I assume that what's in the modern literature is reasonably accurate, but you'd need to ask a specialist. The National Bat Habitat Survey (early 1990s), National Bat Monitoring Programme (1995-2000), and the fact that bats are relatively visible and accessible during hibernation might mean that population estimates for British bats are more accurate than for most other small mammals.

Thanks, Darren!


verderon is the local name, a sparrow-like bird

The English name of Carduelis chloris is 'greenfinch'. But, like other true finches (Fringillidae), it doesn't nest in cavities.

More off-topic bat'n'cat stuff; those who only care for archosaurs - extant or extinct - need read no more of this post.

I took a look at the National Bat Monitoring Programme's Annual Report for 2004 (which can be found here) and found some numbers to play with. This report provides population estimates for 11 of the UK's 17 bat species. All in all, there were an estimated total of 4,870,000 individuals of these eleven bat species in England, Wales, Scotland, and Northern Ireland (though the figures for NI may be slightly overestimated) in 2004.

In other words, if there are 7,500,000 cats in the UK, there are roughly 1.5 cats for each bat.

If domestic cats in the UK kill an estimated 230,000 bats annually, they remove slightly less than 5% of the total bat population. (Here I'm assuming that cat predation is more or less evenly spread across all these different bat species.)

Whether that predation rate is significant or not is another matter. Bats reproduce more slowly than similar-sized birds or non-flying mammals. But, OTOH, the bats' overall annual mortality rates are also much lower (they have few other important predators, etc.). So, while I'm admittedly going slightly out on a limb here, based on these data I'd hazard the guess that domestic cat predation on bats in the UK, on the whole, does not significantly affect bat populations.

I lack the expertise to properly evaluate your argument, but one thing comes to mind: there are 16 or so bat species in the UK, and many persist only in small, isolated populations. In fact, ALL British bat species - with the exception of the two commonest pipistrelles - have total populations less than 230,000 (a few examples: Serotine - 15,000, Bechstein's bat - 1500, Lesser horseshoe bat - 17,000, Grey long-eared bat - less than 1000). Granted, domestic cats mostly kill the more abundant species, but they also kill members of those less abundant species. And in species with small populations, this could well be significant: I don't know if we know the answer. Cat predation is likely to be just one of several factors involved in the decline, and extinction, of British bat populations.

I suppose "Grey long-eared" was followed by "<", which was interpreted as HTML and got eaten, together with everything that followed it?

By David MarjanoviÄ (not verified) on 04 May 2009 #permalink


In fact, ALL British bat species - with the exception of the two commonest pipistrelles - have total populations less than 230,000

According to the report I linked to, the estimated UK population size of Daubenton's bat Myotis daubentoni is 560,000, and that of brown long-eared bat Plecotus auritus is 245,000. As for the estimated population sizes of the pipistrelles: common pipistrelle Pipistrellus pipistrellus, 2,430,000; soprano pipistrelle P. pygmaeus, 1,300,000.

the decline, and extinction, of British bat populations

Decline and extinction? The tone of the 2004 report is rather more optimistic, at least as far as the overall trends for those 11 monitored species are concerned. Some UK bat species* even seem to be increasing. The report's summary says: "Although monitoring is still in its early stage, significant upward trends have already been identified and it is pleasing that no significant downward trends are in evidence" (p. 47). Only one bat species, the greater mouse-eared bat Myotis myotis seems to have become recently extinct in the UK (although a resident individual has been present at a hibernation site in southern England since 2002).

* Lesser horseshoe bat Rhinolophus hipposideros, Daubenton's bat, Natterer's bat Myotis nattereri, and common pipistrelle.

Wait, what was this post originally about again? Oh yes, dead passerine chicks on the ground. I have found them too, on a few occasions. But as they were under large trees, I just assumed that they had happened to fall down and thought no more of it. It never occurred to me, before reading this post, that there was something that needed explaining. As for what have been proposed here so far as general explanations of this phenomenon, I kind of like the 'ejected by cuckoo' hypothesis (even though it wouldn't apply to the case that Darren's posted about here).

In Alberta, Canada I have found two dead baby birds in the front yard
and two in the back yard in the last week.
They are dead and are being dropped by adult birds.
Sorry I do not know enough to tell you if the birds are the same species.

I found some birdfs that found out of a tree but the tree is too high to put back so i put them in a bucket and feed them worms their mother still feeds them what should i do?

By bird savers (not verified) on 01 Jun 2009 #permalink

If the parents are visiting the babies, you should be able to now let things alone, but - if possible - re-position the bucket so that it's partially concealed (and hence the babies are safer from predators and not exposed to the elements), and so that the babies can get out if they want to.

Check the nest for a cowbird chick.

By Jackson Landers (not verified) on 11 Jun 2009 #permalink

Can anyone tell me why a bird would let her 3 baby birds left to die? Yet keep returning to the nest after they are already dead?
This nest was in one of my hanging plants. The mother bird kept feeding the babies, but yesterday when I went to check on them all three of the babies were dead. This morning she kept flying into the nest and back out chirping loudly.
Should I remove the nest?

By Amy Nichols (not verified) on 16 Jun 2009 #permalink

My cats will find and play with dead birds or animals, move them some distance, and then lose interest. Fairly often they bring them into the houseâsee "What the cat dragged in" for a few examples. (They have a cat door.) So you can't count on a precise location.

Incidentally, they also bring in lightweight toys, earthworms, and lengths of weather-stripping.

As to interspecific aggression, Jack Miner (a Canadian naturalist who started the first bird-banding program here) noted seeing a sparrow attack and kill bluebird nestlings and take over the nesting cavity.