April 2007: An Update
NEITHER OF OUR PAIRS OF OWLS is breeding this year, so after all that effort equipping nestboxes with cameras we'll have to wait until next year, 2008. But something fascinating has emerged about the main nestbox pair -- the parents of Owly and Sophie and of last year's two little bairns shown on the right.
The Nestbox owls
Several inspections of the nestbox earlier this year showed that Mrs Owl was almost certainly visiting it but for some reason was not laying. Careful examination of three nearby crows' nests showed that she wasn't using them either. By April 15th, her latest-ever laying date, I was becoming seriously worried that she might have lost her mate. Adults have a 25% chance of not making it through from one year to the next, and we've now been following this pair for four years. The only way of finding out was to spend a night out with listening gear, and that's what I did on the night of 24/25th. The tent is still pitched under the nestbox and I set up my dish microphone and camcorder, both trained on the nestbox to catch her if she came in -- I wanted at least to be sure it was her and not him who was visiting and making a "scrape" in the litter. The dish mic is a powerful beastie, and although it's trained on the box one can hear what's going on for hundreds of yards around. The camcorder has a supernightshot infrared setting that allows one to see quite well into the box.
Quite soon into the night, about 11.30 pm, I heard her calling in a place she often calls from when in the vicinity. Her mate answered from near a house about 150 yards directly behind me and about the same distance from her. But then I heard another owl that seemed to be with him, making a single call immediately after one of his hoots. It sounded like a female or possibly a young male. I heard the parents twice more during the night, at about one and a half hour intervals. They weren't nearby, and on the second of these occasions I again heard this third bird with the male. This time they were near another house several hundred yards from the first. Also, Mrs Owl was clearly moving around, so she wasn't on some nest I didn't know about.
Then finally, soon after dawn, two females briefly visited the nestbox area, kewicking (see mp3 below). In fact I only realised later, when I listened to the recording back at the house, that it was two females and not just Mrs Owl, as I had thought. So what's going on?
There are two plausible solutions. The obviously appealing explanation is that one of last year's fledglings is still going around with her parents! The other, more likely, alternative is that Mrs Owl is now sharing her mate with another female from outside the territory. This has been reported (e.g. Mikkola Owls of Europe p. 143,* and is known behaviour with Barn Owls). Parents allowing a previous season's fledgling to stay with them is, as far as I know, undocumented, so if this has happened here it is a fascinating development. It would be nice to think that the parents were so pleased to have bred successfully at last that they've allowed one of the fledglings to stay on. I shall keep an ear out during future visits to Kent and report any further findings.
Two females visit camp 300 kb mp3 @ 160 kb/s
Top: The two chicks born last year. They were the first chicks the parents raised successfully in four breeding attempts up to that time.
Middle: The first chick to fledge.
Bottom: The proud mother.
(Pics are not clickable. Larger versions are available in the Diary on pages 20-21)
* All we are told by Mikkola is that Scherzinger (1968) "found two Tawny Owl females nesting about 50 m apart and sharing the same male." ("Bermerkenswerte Paarbildung beim Waldkauz (Strix aluco)", Egretta 11, 56.) Other reports on the internet suggest that polygyny is not uncommon with Tawny Owls, though one has the problem with such web information that it may all be based on one source. See also "Comments by an expert" below.
The Pine Nest owls
As to the other pair, the Pine Nest pair, or the House Owls as we now call them, they are safe and well but have also decided not to breed this year. I have no idea why and there are no clues. Last year their nesting attempt failed because, we think, the eggs were infertile. However, we frequently hear them around as the female roosts within 50 yards of the house and the male some way further off. So with this pair too, who were provided with a nestbox this year, we have to wait until next year for further developments.
I asked a leading British expert on Tawny Owls what he made of this situation, and he kindly emailed with some useful information based on the study of ringed birds.
I think it’s most unlikely that the ‘extra’ female is from last year’s brood (do you know that a female was reared last year?). I know of no instances where young tawny owls have not dispersed from their natal territory by the autumn. Also it is most unusual for tawny owls to recruit [be taken back (ed.)] into their natal territory. We have only two examples in about 200 natal dispersal records – so about 1% of juveniles that survive to breed. In contrast, there are a few records in the literature of two females being associated with one breeding attempt, and I once had two males around a nest box with chicks. I suspect your food-supplies must be very low if your birds have failed to breed.
So, that appears to put paid to the idea that the female is one of their own offspring. It's difficult to argue with simple statistics! 200 is a fair-sized sample and quite enough to give a good idea of what does happen and what doesn't. It's a fact that there's a plentiful supply of tawnies in our area. In 2005 we recorded two adult females apparently keeping each other's company right next door to the nestbox owls' territory. This was in early June, and it's safe to assume they were adults as neither was making the type of call that recent fledglings would be making at that time of year. Not only that, in 2006 there were three tawny pairs on the other side of the nestbox owls' territory, so by last autumn there may well have been an unattached female who found her way to their patch and was accepted for some reason.
Anyway, what is beyond doubt is that there is a second female in the territory at the moment, and that she is moving around in the company of both resident owls with no objection from either. What I do not know, unfortunately, is when this situation began. Equally frustratingly, as we don't ring our owls there'll be no reliable way of establishing who the second female is. (Appearance might give a clue but would be quite unreliable as all our local owls are likely to be cousins of one degree or another!) The main interest, therefore, has to be whether the menage a trois will continue and, if it does, what will happen next spring when breeding time comes round once again.
But Barred Owls (Strix varia) may do it . . .
From the owner of the well-known OwlCam comes the interesting information that he is more or less certain that in 1999 his two owls, Ward and June, took a season's break from breeding because . . they had the previous year's two youngsters in tow! Well, more strictly, they didn't breed that year and four owls were heard in Ward and June's territory. He writes:
This was the one year when they skipped nesting and there were clearly four owls in their territory throughout most of the summer. For reasons explained in my 1999 account, I concluded that the two “extra” owls were the juveniles from the previous year. [A Barred Owl expert] told me that this sometimes happens with barred owls.
Further (earlier) thoughts and observations can be found on his website page here.
AS FAR AS I KNOW both our local pairs (nestbox and house owls) are alive and well. For one reason and another it hasn't been a good year for getting out with them, but in August, on one of the Perseid meteor shower nights, I did manage to spend a night out and had the great experience of having the female house owl shriek from a perch almost on top of me! Unfortunately I was still settling down from moving my own perch and my recording of her is ruined by fumbling noises with the mic. Drat! Her voice is so instantly recognisble there's no mistaking her. We quite often hear her mate from the house, so all is well with them. As to the other pair (nestbox), I think I heard them the same night -- owlwise it was rather quiet -- but I need to do another night out some time to check. Now it's autumn chances of hearing them should be better.
Over the summer the main nestbox got stuffed with leaves again by the local squirrel! We've emptied it since and it's ready for occupation by Mrs Owl. More alarmingly, some local brat investigated the site this summer, opening up my tent and cutting one of the pieces of brown garden string that tie the video cable to the beech trunk on its way to the ground. Luckily no further damage was done and things have been left alone since. But discovery of the site by some such moron has always been a worry. The nestbox is reachable by someone determined to do so and evidence that someone had climbed up would oblige us to move it. This would be a great pity as the current location is ideal.
I know roughly where the female house owl roosts during the day, but despite a couple of thorough searches it's been impossible to locate either her or any evidence (poo) that might give away where she hides up. We know she's somewhere there because we hear her when she becomes vocal at dusk! It's remarkably hard to sight tawnies during the day -- apart from nesting time we could count sightings of our two pairs on the fingers of one hand.
Last month (Sept) the company that owns a power distribution line that runs right through the wood sent in a team to clear the ground underneath it. It looks like they used a machine that literally eats trees and everything else! So now there's a 10-yard wide swathe of mashed-up brown litter-covered track running for 100s of yards, offering unprecedented access to new parts of the wood, some of which are otherwise impenetrable. But these power lines have always worried me as perching on one of the metal cross-bars would put a large bird like a tawny at great risk. With the cleared ground beneath, the bars offer a tempting hunting post. In some other countries power companies are now obliged to install safer setups on the tops of poles, but not here in the good old UK it seems. We need lots more dead birds before that'll ever happen. If you look up "bird electrocution" on Google you'll find some horrible things. I just don't want it to happen with our owls. It's the one big risk they face in their territory, which is otherwise pretty safe. (More on this hazard below.)
So, we're heading slowly but inexorably towards next spring and another owl nesting season. I want to make a third nestbox -- following the very nice design from Holland on this Nestbox section page -- to put up for a third pair living in the north of the wood. After the holiday from nesting taken by both our other pairs this year I want to maximise the chances we're going to see some babies in 2008!
There've been signs since the summer that the nestbox site has attracted the attentions of an, I would guess, young malefactor, and sometime shortly before Christmas a major effort was made to extract whatever was in the nestbox (a camera) by yanking hard on the video cable. Fortunately whoever it was got nothing, and the nestbox attachment held, but as these tamperings have shown growing determination over the months I became worried that the next obvious step was to climb up into the tree -- easily done by standing on a box to reach the lowest branch.
So, reluctantly, we decided to remove everything on the site and relocate nearer nesting time. We can't defend ourselves, or the owls, against this sort of thing other than by better concealment. Fortunately there's a site not far off that's much more concealable. And what this little boy, or boys, don't know is that our next-door neighbour in the woods -- the guy who keeps the guinea-fowl -- is a member of the county constabulary! As the nestbox will be going within sight of his big pen he'll be able to keep an eye on things when he's around.
Left and middle: The video cable had been pulled hard, breaking all the string that tied it to the beech trunk. Only some tough connectors stopped the camera being pulled out of the box. Right: Cable was pulled out of the ground all the way to the tent, which had been opened up to see what was inside.
Left: After three years in the beech the nestbox spends its last hour there -- on Boxing Day as it happens! Right: Safely back at base. We brought the tent in the next day.
More hazards for the owls
As if the depredations of the vandals weren't bad enough, I'm almost more concerned about another hazard that's been there all the time but which has been made much more risky for our owls because of scrub clearance beneath it. This is a transformer behind a house. It's at the edge of the wood and, for a bird, on a natural flight path into the wood. The scrub (thick heather and bracken, and in places sapling alder and birch) along the entire course of the distibution line through the wood has been cleared to the ground, so the poles and the transformer box now offer predators like owls tempting sites for perching while hunting.
Have a look at the transformer. It's terrifying. Nice flat top to perch on, and all an owl has to do is to stretch and touch the unprotected cable with a wing tip to receive a lethal 11,000 volt shock. There are now many, many recorded instances of birds being killed by these dangerous unprotected domestic transformers. The situation with the other poles carrying the lines isn't much better, with a metal cross-bar almost guaranteeing that a luckless owl wouldn't stand a chance. In the US they're well aware of the threat to raptors posed by unprotected transformers, and in many states steps are being taken to make them safer. But not here in good old blighty.
The owls whose lives are at risk are our magnificent nestbox pair, Sophie's mum and dad. Most of the year they hunt in the fields and don't come into the wood. But the transformer box is on a route into the woods that the male may take during nesting time, and who knows, he may be tempted to stop by to check its hunting potential. I'm wondering if a letter to the local electricity board will have any effect.
Unprotected transformer boxes, like this one for a nearby house, can be lethal to any medium to large bird that sees them as a useful perch. If a wing so much as brushes one of the offtake cables it's finis. For our owls the risk is greatly increased by the recent clearance of the ground along a strip 10 yards wide through the wood all along the distribution line, including underneath this transformer, opening up a tempting new area for hunting. For a largish bird the box also happens to be right on a convenient entry point into the wood.
And the owls themselves?
The house pair are fine -- I recorded them over Christmas, the female instantly recognisable from her excited way of kewicking. The main wood pair -- the nestbox pair -- I don't know. I haven't had the chance to go into their area at night since the autumn.
Today, starting back to London, I nearly had a bad shock. In the road just outside the house drive was a large bundle of darkish feathers. This is right next to where the house owls roost. Not until I was almost up to this pathetic bundle did I see it was a pheasant. Part of one wing was fanned, and I'd thought it was an owl's tail. My heart was absolutely in my mouth. I guess the owls have survived so long because there are tall thin oaks both sides of the road, and if they cross -- which they certainly do -- it is probably in the crowns 40 or so feet up.
They're back, so we have a new Tawny Owl Nesting Diary 2008.
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