20.02.2020 - Owls and the BTO Owl Project

Speaker: Dr Hugh Hanmer
Reporter: Cath Robinson
One of the benefits of the BTO being based in Norfolk is that we seem to have a limitless number of speakers for our club! Tonight, we had a full house to hear Dr Hugh Hanmer who among his many responsibilities has been coordinator of the Project Owl scheme. He started off explaining some of the charm of owls with their appearance; massive eye sockets; amazingly flexible necks; adapted wing feathers which help deaden flight noise, but he thought as there was very little space left in the skulls for brains maybe not so wise! ​

But as he emphasised throughout the evening, they are very difficult to study because of their behaviour. As they are mainly crepuscular or nocturnal then the traditional surveys which depend on daylight sightings are not very accurate (so all estimates come with a health warning) and in fact, may not be representative as for some owls, daylight sightings may not be a sign of healthy behaviour. So, as well the breeding bird survey, the BTO is dependent on periodic dedicated surveys. He then went through our British Owls, giving a general background to what was known (or indeed not known) about each, based on what surveys had shown. Tawny Owls are our most widespread and numerous, with an estimate of 50,000 pairs but declining. They’re fairly static (a ring recovery in Iceland was a keepsake from someone’s binoculars!) Nest surveys show a fledgling rate increasing over time and adult longevity is stable, but as (daylight) surveys have suggested they are in decline, there must be issues restricting the juvenile population reaching breeding age. Why? Little Owls are not native, and I got the impression that he wasn’t as concerned about their fate! Certainly, there didn’t seem to be anything in the owl project plan about them. Another static owl, estimated pairs are 3,600 (in 2016) and declining. Again, fledging rate is increasing and adult survival rate is stable. Why the decline? Maybe a reduction of prey? Short-eared Owl estimates 600-2000 pairs and declining. There is an influx in October and November with a drop off at the end of spring. They are clearly mobile with the furthest ring recovery in Russia. But we know very little. Long-eared Owls estimate 1800-6000 pairs but we really have no idea. They are probably grossly under recorded. There is a peak in recording in February and October and inward migration in Autumn seems to be mainly females. Some European countries have winter roosts of dozens; in the UK it’s more like 6. They are mobile the furthest ring recovery again in Russia. Barn owl. A Conservation Success Story! Yeah! This species has gone from amber to green and the population has gone from 4000 pairs to maybe 14000. We have lots of data about them partly because of their use of nesting boxes. They have had an increase in fledging success, stable survival rate and can double brood, so if there is a slump they can recover well. In the second half he focussed more on the gaps in our knowledge and how we were going about trying to tackle them. Project Owl is about using science and communications to get greater engagement of volunteers thereby getting better data and focussing on priority projects. For the Tawny Owl, the plan was to get better data encouraging more volunteers to provide it. (And some of us club members were some of those volunteers.) So more dedicated surveys (last done in 1989 and 2005): The first was a structured survey of targeted survey squares to compare back to the older ones. Volunteers were asked to record “detected or not “between mid-August and mid- October 2018 on at least 2 occasions for 10 minute listening periods within 2 hours of sunset, which would be peak vocal activity. There were 2900 tetrads and 2120 volunteers, an impressive turnout. It looks like there maybe a 10% occupancy decline since the last survey but they are still very common. Norfolk records are similar to the rest of the country with 56% of squares being occupied. The second survey was a calling survey which was overwinter 2018/19 and there was a big publicity campaign to get more volunteers to become involved and participate. There were about 9500 surveyors and 85% heard an owl. The very best time to hear one is on a warm cloudless brightly moonlit evening around dusk near a tree/woodland. Hugh promised us a report on both surveys in the next BTO news.
Technology-wise, we also learnt of the use of Passive Integrated Transponders (PIT) tags so you can follow tagged birds as they fly past the scanner. This is especially useful for getting information on males which are otherwise more elusive than females. But, of course, these are expensive. With the Short-eared Owl, as they are hard to survey, the plan was to look at habitat use and movement to see what they need. Direct observation is cheap but not very effective; VHF radio telemetry still requires volunteer time and is a bit expensive; and (solar powered) GPS satellite tags are very expensive (£3K each plus) but give great data. Tracking shows that the birds spend most of their time on grassland (rather than heathland) but roam further at night. Non-breeding times have shown huge movements; one mid-Scottish female roamed around central Scotland her first year then bred, left the male to fledge the chicks, went to Norway, attempted to breed there, then went to Ireland, then to Dartmoor, then to Norfolk, then back to Norway, and then stopped recording maybe caught in a storm. One tagged on Aran went to Morocco. Long eared owls: The plan here was just to encourage recording. There was insufficient funding for a survey and while it would seem ideal to do a track on them, GPS solar powered won’t help for a nocturnal bird. Hugh had no answer to how to find one: just look and be lucky! Your best chance might be to hear the chicks “squeaky gate” calls in the summer. Hugh ended by re-emphasising the number of gaps in our knowledge on population sizes and trends; on demographic gaps on habitat usage; and a plea to us to submit records ideally on BTO Birdtrack but anyway to County Recorders. Many thanks to him for such an entertaining presentation.