Mysterious death of two owls

Here is a fascinating article from the Bognor Regis Observer about the death of two Tawny Owls that has me pretty much baffled. It was written by Richard Williamson. My own comments and suggestions follow the article.

Click the Bognor Regis Observer mast to see the original article on the Observer's website. For convenience it is reproduced below.

Bleak winter

Published Date: 03 December 2009

<< What could have killed these two tawny owls found dead in the wood around my home? My wife is holding one that was just barely alive, while the other lies dead beside her. The first we knew of the incident was when a reader approached me in Waitrose and said that during an early morning walk past my house she had seen two owls next to the path, lying quite still. There appeared to be no wounds or damage.

Reaching the spot an hour later, we were quite puzzled by what we saw.

Both birds were lying on the bank facing one another, almost touching. They were in perfect condition, with not a feather ruffled. Their eyes were still bright black when lids were peeled back. They had no wounds, no broken bones, no apparent sickness of any kind. In cases of poisoning for example, birds may vent abnormally and have dishevelled feathers around the vent. One was dead, but one still alive, though unconscious.

When Anne placed her finger under its beak it nibbled the skin gently. Within the hour it was cold. You can always tell if a bird has been shot with a shotgun since wing feathers will have broken shafts. Even the barbs on the shafts will show fracture, while somewhere amongst the feathers you will see the odd wound or patch of blood. The birds had not been trapped in a cage because their faces and wings were quite perfect, the feathers unbroken anywhere.

Why were the birds together? This suggested that two males had been having a fight. In autumn they are very busy claiming new territories. Summer young are trying to fit into available space and that may be limited. But their enormous talons and hooked beaks had not been used in anger recently. The RSPB were unable to help really. As poisoning did not seem to be the cause, nor other human malpractice, this could not be considered a wildlife incident when the police would need to be involved.

Anyway, why would the birds be so close together if they had suffered poison? They would be off into corners by themselves. Years ago I used to take dead bodies of animals to a laboratory in Surrey for post mortems. There usually had to be large scale incidents of several specimens together to make the work worthwhile. Even so, I did have one or two roe deer tested, when the autopsy showed that they could have died from any combination of up to 50 pesticides present in the carcass. I am talking of the situation 25 years ago when pesticides were far less controlled than today.

So the two dead owls near my home remain a mystery. My wife, who suspects the unexpected ulterior motive every time, thinks these two birds were somehow destroyed by a human, and dumped on the side of a public way for whatever reason they might have had. Is there anybody out there who knows what happened and can give a clue with anonymity? Meanwhile, another reader from Lordington has just reported finding a perfectly pristine adult tawny owl near her home. She could find no mark on the bird. Are there any others?

The tawny owls in this wood have not declined: the same birds which call every night are still calling here, which does suggest that our two casualties have been imported for some obscure reason. In the past summer, populations of small wood mice and also yellow-necked mice have crashed. For the first time here in 40 years the yellow-necks have not been thumping about at night over the bedroom ceiling. All has gone very quiet suddenly. Owls may have a bleak winter ahead, but starvation does not seem the cause of these two deaths. >>

Comments

This really is most mysterious — yet there must be some reason why the owls were found as they were. The problem is that all we have are observations by someone who is clearly a competent and experienced observer but no analysis by a veterinary bird specialist or lab. Let’s consider some points.

First, were the birds dumped?

Initially I thought this was the most likely. But on the basis of the evidence the answer must be no. It would be almost impossible to carry two Tawny Owls — whether in a bag or not — without causing feather disarray and damage that would be quite evident. Also, if these were two captive birds that someone did not want, they would show signs of feather damage at the tips of the primaries and tail feathers characteristic of owls kept in a mesh cage. So we have to assume they were wild birds.

The next problem — no missing local owls

We have to take Richard Williamson's word for this when he says “the same birds which call every night are still calling here". Without a local map showing owl territories near the house and where the owl bodies were found it is impossible to judge, but if these owls were intruders into the territory of a resident pair within earshot of the house it’s unlikely he wouldn’t have known about them — through the noisy squabbles that would have resulted. Conversely the possibility cannot be ruled out that the dead pair were local residents who were displaced by another couple who took advantage of the local pair’s declining health and moved in. In either case there would be no net change in the number of local owls.

The problem with these explanations is that there’s little evidence that settled pairs change territory like that. They tend to stay where they are.

So who were these owls?

How then do we explain two local owls who kept each other’s company but whose presence had gone undetected? The most plausible explanation I can think of is that they were two yearling females who were still going around together. They could have been born to a local pair or they could have come in from outside. As females, they may be tolerated on established owl pairs’ territories and they can go undetected by humans as they don’t use the piercing kewick call but a quieter version of the hoot that doesn’t carry far. They also may not call often — presumably because they don't feel “at home”. Unfortunately we have no information on the sex of these birds.

Death in the same place at the same time?

First, I have no problem with the owls being found together. Tawny Owls, including young female pairs, are very companionable and I wouldn’t see that necessarily changing in whatever brought this situation about.

So we have to account for the fact that they died within hours of each other.

A fight? Extremely unlikely. I’d rule this out on the basis of the evidence of absence of physical damage given by Williamson.

Shooting? Again, no on the basis of the evidence.

Some other physical cause? For example collision with each other or with a branch. We have to consider this, but again it can be dismissed because of the plumage condition and lack of blood around the beaks, which might be expected in a case of lethal collision. However broken bones in the body are much more difficult to assess, unlike say wing or leg bones.

Starvation? No real evidence given, but it’s unlikely that two owls would have starved to death at more or less exactly the same time. It’s also unlikely that they would be found in a location and position giving such evident signs of distress like the two owls here.

Poisoning? Here there are two possibilities: plant and human agents. Plant matter would include poisonous fruits, like deadly nightshade or mushroom; human-set poisons are mainly the rodenticides (Wikipedia: general article; brodifacoum; American Bird Conservancy page on brodifacoum poisoning in birds; Owl Pages article on ingestion of brodifacoum by owls) and organophosphates, which are known to affect birds generally and raptors specifically.

Ingestion of poisonous plant matter cannot be ruled out as some owls, including tawnies, do eat fruits and leaves (YouTube videos: Great Horned Owl; Tawny Owl). Mushroom poisons are numerous and produce a wide range of symptoms, often but not always including vomiting and diarrhoea. In any case I wouldn't expect evidence of diarrhoea around the vent as owls are designed to eject even very liquid wastes cleanly — and I can assure you that they frequently do!

Ingestion of rodenticides can be direct (consumption of pellets) or secondary (by consuming poisoned rodents or carcasses). Secondary poisoning has the problem that it’s less likely that the two owls would die at the same time than if poisoning was by direct consumption. It can’t be ruled out of course that these two owls consumed some other poisonous agent that they found.

The attraction of the poison explanation is that it can account for the nearly simultaneous deaths of the two owls, their otherwise good condition, and the evidence of distress — the very unusual situation in which they were found, so close together on the ground.

Finally, illness

Again, two lines here: parasite infestation or some viral infection. I’m not qualified to comment on these except to say that if it was one common parasite infestation (a throat parasite that can be picked up from Wood Pigeons) there would have been evidence of starvation. Obviously a viral infection is plausible because it offers an explanation for the nearly simultaneous death of two birds that were going around together and, once more, the evidence of distress. One might, of course, expect the deaths of other local owls in this case.

Afterthought . . .

Despite what I have written, I do find this picture of two owls lying down to die side by side on the bank by a public footpath very odd indeed and just too unlikely. The "cause" that comes overwhelmingly to mind is that they were in fact placed in that position by someone. For the reasons I have given I would still rule out the possibility that these were two captive owls someone wanted to dispose of, so all I can suggest is that an earlier passer-by walking along the footpath, perhaps with a dog, found the dying owls further back in the wood and laid them on the bank, possibly in the hope that someone else — like Richard — would come by and be able to do something for them.

Comments welcome. Mail to raham [at] btinternet [dot] com

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