The Accipiter - Research September 2005

Research - September 2005

These important occasional special features will focus on the work our residential students do with and for us. The owls have been examined, released, and are now being monitored. Here is the story so far ...

Tawny Owl release programme report

Seven of the Owls in the Pre-Release Flight Aviary

The tawny owls were ready and waiting for us in their foster aviaries when we arrived at the Conservancy, blissfully unaware of the rigours they faced in the weeks ahead. We were eager to begin, and plunged into a hectic first few days. The immediate task was to capture all our charges and determine whether they were fit to be released. In total 16 were deemed suitable for release and were fitted with British Trust of Ornithology (BTO) rings. They were also weighed and had their wing lengths measured to determine their sex. At this point 5 of the owls were boxed up ready for release that night in Chawton Park Wood near Winchester, and to farmland near Kingsclere north of Basingstoke, while the other 11 went into the pre-release flight aviary.

Transmitter Attached to the Deck Feathers

After a couple of days we brought all 11 owls into our hospital to have their transmitters attached. We formed a conveyor belt each holding 1 or 2 tawny owls, which waited patiently for the attachment of their tail-mounted transmitter. During this process they had their photos taken for our records and for displaying to the public. We also gave each owl a name, choosing the theme of naturalists and people associated with animals - so for example 'Saba' (Saba Douglas-Hamilton) and 'Packham' (Chris Packham).

They were caught for the third and final time on the day of their release, and we checked that their transmitters were securely fitted. Two were found on the floor of the pre-release flight aviary and were firmly reattached with plenty of glue. The owls were boxed up for release into local woodlands and in the evening four were taken to Sarson Wood, three to Amport Wood, two to Gollard Copse and two to Furzedown Wood.


Owls being released at Gollard Copse (1.1MB)	Owls being released at Sarson Wood 1 (2.5MB)	Owls being released at Sarson Wood 2 (2.7MB)	Owls released at Sarson Wood (2.1MB)

Our initiation into the use of the telemetry had been good fun, with two of us hiding transmitters around the park for the other two to search out.

Practicing Telemetry in Reg's Meadow

In the woods however, locating the owls initially seemed like looking for a needle in a haystack - too many trees to choose from. The first day of tracking was a long one, although by the end we felt fairly confident we'd found all the owls, if somewhat imprecisely. The next day we were slightly faster, and the day after that we even had time for lunch back at the Conservancy. The worries we had about our inaccuracy with the telemetry were heightened by the concern that we wouldn't find the bodies of any owls that may have died very soon after their release. We were told to expect a high mortality rate and so kept our eyes apprehensively peeled for small tawny owl corpses as we scrambled through the woodland under-storey.

By the second week our tracking had improved considerably, and we were confidently striding towards roost sites to record the exact location with the GPS (Global Positioning Systems). We found that hardly any of the owls had moved far from the release sites by this time, and although we were pleased to have them close and presumably alive, there was always the slight concern that the owls may not be exploring and dispersing in the search for a territory in the way their nature dictates. We knew the tawny owls had, at most, a week's fat reserves from the day we'd released them, and that if their instincts had failed to kick in strongly enough for them to begin hunting for their meals, we could expect to find quite a few bodies from about day 7, perished as a result of starvation. But we found none, and grew more sure of our owls' vitality as we rarely tracked one bird to exactly the same spot two days running - they were nearly always at least a few trees away from their previous roost sites. Every night we plot the location of each bird on a fresh map, using grid references from the GPS, and these maps allow us to see the subtle or occasionally more epic movements of every owl.

While this is a simple enough system when the owl is found in an accessible part of the woodland we have permission to enter, some difficulty arises when an owl decides to roost either in a heavily vegetated area, or else in trees in other private property. This problem was in part responsible for the delay in finding the first (and so far only) fatality. Bellamy (A11), was found dead in the grounds of a property on the east edge of Amport Wood on 10th August, but may have died up to 10 days previous. It was therefore not possible to determine the cause of death, but it is most likely that she died of starvation. Smoke inhalation from a nearby bonfire was also suggested as a possible cause.

Bellamy (A11)

Bellamy's death was rather upsetting, as we'd allowed ourselves to become quite optimistic about our owls' survival following the success of the first twelve days or so. After this, we were scouring the ground anxiously again in all the woods, convinced there may be more undiscovered bodies wrongly diagnosed as being alive. But the next few days revealed no more fatalities, and in fact our optimism was renewed when we began to catch regular glimpses of the birds. At first this was usually just a fleeting glance at an owl hurriedly fluttering away through the treetops, causing great excitement for us. This began to happen more often, and made us wary of disturbing the owls too much. We subsequently grew much quieter and more cautious in our tracking, and were rewarded with sightings of our tawny owls roosting in the woods.

The first owl spotted was Darwin (A04) in a woodland corridor north of Amport Wood, on 11th August. Surprisingly, she sat very low in a sparse young tree, allowing for a close look and even a few photos to be taken.

Darwin (A04)

Seen Roosting in a Hazel Tree North of Amport Wood Since then we have seen several of the released owls, and managed to get photos of some for our display boards. We have been consistently surprised by how often the owls have been perched not much higher than head height within trees that offer little cover, and that they will tolerate us coming so close. Is this a sign of apathy from illness or starvation? This is something we need to consider, although their continued persistence some time after being sighted suggests not. Another possibility is that the owls have lost a degree of their fear towards humans following their early experiences of being near people, or even just that in their stillness and silence they feel reasonably assured of their safety. Continued sightings of our birds have helped to affirm that they are alive, as there can always be a margin of error with our tracking.

Despite only one confirmed death, 'missing signals' further reduced our quota of owls to track. Less than two weeks after the release, signals for Attenborough (A08) and Durrell (A10) disappeared.

Oddie (A01)

We spent many mornings thereafter driving around the whole area searching for the escapees, but to no avail. It is impossible to say whether the missing signals are a result of the owls dispersing a long way, or damaged transmitters. Either way, we may never be able to confirm these owls' survival. Additionally, the transmitter for Oddie (A01), a grey-morph, was found on the ground near Foxwood Lodge in Sarson Wood on 22nd August, so this owl's fate may also never be known. We have assumed that this transmitter was naturally dislodged, rather than removed during a struggle with a predator, as there were no feathers or flesh attached. A sad sort of poignancy surrounded the discovery of this transmitter (although Ashley was delighted as this was the only transmitter he hadn't personally attached!). Oddie was alone in the wild, free of her observers, and we would never know what became of her. She was the most distinctive of the bunch, with her pretty grey face.

Currently we have 7 owls still going strong, which we consider a success. Anything could happen in our last week of tracking, so there will be a full update as well as a review of our findings in the next article.

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