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Thursday 23rd October, 2014

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Research And Rehabilitation Telemetry

Thanks to the legacy of Pat Hoad, we have been able to purchase some telemetry equipment this year. Many of you may be more familiar with the term radio tracking and will have seen wildlife programmes on TV where collars containing a radio transmitter are attached to elephants or big cats and their movements followed using a radio receiver. With birds there are 4 types of tags used. They are: necklace, back pack – a Kevlar harness with a tag attached, a tail mounted tag which is attached to a tail feather on the bird or a leg mounted tag.

Hunting Area
Photo courtesy Sue Thurley

Here at the Trust we often receive birds that are hungry or concussed and after a spell in our wildlife hospital they are ready to be returned back to the wild. We now have a specially designed soft release aviary which is installed at release sites and the rehabilitated birds are kept in this aviary for about a week before final release.

Earlier in the season a barn owl was brought in underweight and weak. Once fit and healthy and ready for release, we wanted to find out how effective our rehabilitation techniques were. We were curious to know whether the owl would disperse as soon as it was released or stay in the vicinity of the release site. We decided to use a leg mounted tag as recommended by Biotrack.

The longevity of battery life was forfeited for a stronger signal from the tag which had a battery life of approximately 5 weeks and was fitted to the leg of the bird whilst still in the soft release aviary to monitor any effects on the bird.

Soft relase site
Photo courtesy Sue Thurley

After a week on a warm still night with only the midges and a night vision scope for company, I returned to the aviary to release the owl. Carefully I removed half of the roof of the aviary trying not to startle the owl. Then I waited.....and waited ....... and waited.........

Our owl didn’t seem at all bothered about freedom! Finally at around 1.00 am I went home to get some sleep.

The next morning, worried that something may have happened to the owl in the early hours, I rushed to the release site at about 8.30 am and to my relief the aviary was completely empty. Now the fun really would begin!

The principles of telemetry are that a tag attached to the bird or animal emits a signal of a specific frequency and this signal is picked up by a radio receiver. By using a large aerial and the receiver, it should be possible to pick up the signal and work out which direction the tag is in. Sometimes it is necessary to take a bearing of the signal using a compass and then move to another spot to take another bearing. Where the two lines cross is the location of the tag.

Telemetry Tag
Photo courtesy Sue Thurley

The strength of the signal can be reduced or lost completely if there are objects between the tag and the receiver. The signal can also be reflected by objects. It was not uncommon for me to wander in completely the opposite direction to our owl as the signal was being reflected by trees or buildings. Radio waves can sometimes be diffracted by impenetrable objects causing the signal to be slightly off line and they can also be polarised.

I tracked the owl every day for 2 weeks and then every other day for a further 2 weeks. Sometimes it was necessary to seek higher ground to get a better signal and other times I had to avoid being followed by cows that seemed to have a disconcerting curiosity for myself and the aerial.

This barn owl didn’t travel far. On leaving the aviary it roosted in an old ash tree and after a few days took up residence in an old barn nearby. It was a fantastic opportunity to study its behaviour and to see it quartering over open fields, hunting for prey. Many of the fields near the release site are used for keeping horses while others are cut for hay. Due to the less intensive grazing regimes in the area there was sufficient habitat for the owl to hunt. However once some of the fields were cut for hay the barn owl moved to roost in some trees nearer to the uncut grassland.

Although the owl never returned to the soft release aviary to take any food left out, it seems to have managed to successfully hunt in the wild once again and has recently been seen quartering at dusk in the same area as it was released.

Sue Thurley

Thanks to Tony Greenhow of Ulverston for allowing us to use his land for the location of our soft release aviary and local businesses, Alan Myerscough, Ford Dealer, Ulverston and Edmundson Electrical, Electrical Wholesalers, Barrow-in-Furness for their help in transporting it.

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The World Owl Trust is a member of the British and Irish Association of Zoos and Aquariums (BIAZA) and the European Association of Zoos and Aquariums (EAZA). The Trust relies on a dedicated membership, visitors, donations and legacies.
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