29C SUMMER RINGING AT WOOLSTON EYES 2012

by Michael Miles

 

Only those of us who have spent the last six months buried in a box will have failed to notice that it has been a rotten summer. The fifty odd species of birds regularly monitored by the ringers at Woolston have differing strategies for survival and passing on their genes and the impact of the poor weather has varied depending on the strategy employed.

 

In the period from April through September the team at Woolston ringed 3,064 new birds compared with 4,206 in the corresponding period of 2011, a decrease of 27%. Ringing effort year on year was broadly constant although a few sessions were lost to rain or high winds. The habitat this year has not changed significantly from 2011 but the success of the application for Higher Level Stewardship funding for No. 3 Bed and the Loop of No. 4 Bed means that major changes will be taking place over the next three months as contractors move in. We expect some disruption to our ringing in the short term but like everyone else with Woolston's best interests at heart, we are excited by the potential to reinstate a healthy wet phragmites bed with extensive interconnected pools on No. 3 Bed.

 

The reduction of 1,142 in new birds ringed is concentrated in two areas. We ringed 324 fewer hirundines. The majority of hirundines ringed at Woolston are caught in the small roost that forms on No. 3 Bed in the autumn. This year the roost was normally around 300 birds, a similar size as in 2011 but high winds reduced the opportunities to set nets in the exposed sites in the phragmites. As has become the norm, we had a couple of "near misses" with a Hobby hunting the roost.

 

The other group of birds where catches were significantly reduced was the warblers. We ringed 1,424 warblers of nine species compared with 2,130, also of nine species, in 2011. Excluding hirundines, warblers accounted for only 48% of new birds ringed as against 57% in 2011. The two worst affected species were Sedge Warbler where catches were down 58% and Whitethroat down 52%. Reed Warblers were not much better with 43% fewer birds ringed. All of these species winter south of the Sahara. In contrast, two species that winter around the Mediterranean fared rather less poorly with Blackcap down 26% and Chiffchaff 16%. In addition, Reed Buntings, which nest in the phragmites but do not undergo a long distance migration were down 21%.

 

For a number of good reasons we do not move around in the reed beds at Woolston and accordingly we do not monitor the performance of individual nests. I have "cribbed" the following from a ringing colleague who monitors a population of Reed Warblers in Suffolk and I believe it can be applied equally to Woolston's trans Saharan migrants.

 

"Winter was extremely dry in the wintering areas and survival was probably impacted. During northward migration there were severe storms around the Mediterranean that caused casuakties and held up migration. Fewer adults returned and first broods were lost in heavy rainfall. Dead females were found on nests containing dead eggs or chicks. Second breeding attempts were washed away by rising water levels. Only at the third attempt did some pairs successfully fledge young". It could be added that some of the young that did fledge showed signs of poor nutrition in the form of "fault bars" in their feathers where they have grown poorly as a result of inadequate food supply. These birds will have undertaken migration with poor quality flight feathers thereby reducing their chance of successfully completing the journey.

 

All of this adds up to a "perfect storm" of adverse effects for these species and we await the return of adults in 2013 with some concern.

 

It is tempting to suggest that in broad empirical terms there is a "weather" effect that has reduced breeding success by about 25% and, for long distance migrants, a "winter and migration survival" effect of about a further 25%. In contrast the resident insectivores have, for the most part, had a reasonable breeding season. Wrens, Dunnocks and Robins were caught in similar numbers to 2011. Blackbird catches were down a little from 65 to 53 but we ringed 46 new Song Thrushes compared to just 20 in 2011. The wet weather has been good for slugs and snails that these thrushes depend on whereas the first part of 2011 was exceptionally dry and first broods suffered.

 

The resident tit species had a fair breeding season in line with 2011. In particular productivity of Blue Tits and Great Tits in the nest boxes on No. 3 Bed was good. This was not in line with national trends and it would be interesting to know why. It seems unlikely that our birds are dependent on the small green defoliating caterpillars to feed to their chicks because we do not see many of them on the bed. It would be interesting to know what insects are fed to the chicks and I am in discussions with the British Trust for Ornithology with a view to having some faecal samples analysed.

 

Amongst the seedeaters, 167 new Greenfinches were ringed, a reduction of 20% from 208 in 2011 and Chaffinches were down 37% from 115 to 72. By September these birds are coming to the feeders or on the ground in the sacrificial crop. If breeding was delayed for any reason they will be later arriving at Woolston so these changes may reflect timing as much as abudance. There was a large reduction in catches of Lesser Redpolls but this species is irruptive and catches at Woolston vary sharply from year to year.

 

It is good to end on a cheerful note by reporting that Woolston's two flagship passerines both had reasonable breeding seasons. The 30 new Willow Tits ringed compares with 35 in 2011 and the 149 new Bullfinches with 158 in 2011.

 

Away from the core species, an increase in trapping effort produced a Mallard, two Water Rails and five Moorhens. Three Sparrowhawks captures was an improvement over none in 2011 but with this species it is more a case of luck when they "stick" in a net rather than changes in population. A handsome adult male Kestrel was a pleasant surprise on No. 3 Bed and the first there for over ten years.

 

Finally in what was probably the most unusual ringing event of the summer Kieran Foster used a flick net to capture 33 low flying Swifts on May 20th. These are the first Swifts ringed at Woolston since 2008 and this is the third highest annual total in 33 years of ringing at Woolston.

 

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