Tuesday, 5 May 2015

Wheatear RAS is on

Most adult wheatears that make it back return to the exact territory that they bred in during the previous season
This is the third season of the wheatear adult survival study (RAS) at Mynydd Preseli and it is very much hoped to get the sample of colour-ringed adults up to 50 this year. This is something that was the aim in 2013 and 2014 but annual totals of only 26 and 30 respectively were achieved. Rather than admit failure though, this underachievement has been classified as an essential learning-through-experience part of the project. The open habitat means mistnets are unsuitable so the birds are caught for colour-ringing in spring traps baited with mealworms.

A few things learnt:

Although some wheatears are caught readily, they very quickly become trap shy and if they witness another individual being caught they become highly suspicious of the traps and become very difficult to catch. During the egg-laying and incubation period the males usually mate-guard the females by following them about whenever they are off the nest, so it is difficult to find a time when females are on their own. Whilst females are on the nest, the males tend to sing and generally loaf around, so they don't spend much time feeding. They are only attracted to the bait when they need it, so on nice warm sunny days when they are often well fed, they ignore it.

If the nest is full of hungry chicks then both adults are much more likely to be tempted by the bait and this is when most birds are caught. However in 2013 the very cold weather in May meant that there were lots of nest failures, and those that were successful had small broods (e.g. brood sizes of 1 and 2 were frequent instead of the usual 4 to 7). The weather subsequently turned warm and dry and this left many pairs not that desperate for the bait.

Once the young fledge, the adults seem to switch from feeding them soft prey to adult insects and aren't fussed about eating mealworms, so they have to be caught before they fledge young. In 2014 the season was surprisingly early and about 50% of pairs had fledged young by the time of the first visit on 24th May.

The secret of catching all the adults lies in timing the catching effort to coincide with feeding nestlings, so regular reccy visits from late April onward are essential to keep a finger on the pulse of what each pair is up to.

Some of the colours fade whilst the birds are are in their sunny African wintering grounds. Red, in particular, fades to a sort of pinky-orange within a year making it almost impossible to tell from orange with certainty. Light blue seems to get much paler and can appear white. Luckily all the ambiguous combinations were not applied to the same sex, so all birds are still uniquely marked.

red over grey in May 2013

The same bird a year later

In 2014, 12 out of the 26 marked in 2013 returned (46%), and so far in 2015, 12 out of 30 have been confirmed, though not all territories have been checked so the figure will almost certainly rise.

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