Friday 11 October 2019

2019 - an overview of Blaenduad and some thoughts on Willow Warblers

I made a couple of casual visits to the Blaenduad plantation in 2018 and considered that it might be a good area to carry out some nest recording in future years. I requested permission to carry out study work at the site and my first visit in 2019 revealed my lack of experience with conifer plantations. Off the main rides, a ‘secret’ maze of drainage channels existed and within 30 minutes I had ended up viewing the landscape from the perspective of beetles, ants and the like. I located a Willow Warbler nest site under construction but soon realised that a broken ankle or worse was also a potential outcome of such off-piste adventures. One sunny morning, I estimated around 50 male Willow Warblers were holding territory.  A further visit to locate a Stonechat nest ended without a fall but also without success. On the next visit I wasn’t surprised to find a newly fledged party of Stonechats and a male Common Whitethroat courting a female, slightly too early for nest construction but they would surely do so. Tree Pipits were displaying (how do they sing with food in their beaks) as the plantation gradually started to come alive.  During some of my initial visits, mist nets were erected in locations where pairs of birds were thought to be holding territory and after three visits, I had ringed 35 birds of 13 species with Willow Warbler, Chiffchaff and Common Whitethroat being the most numerous.

The season progressed and I started to get more familiar with the site. I watched how birds flew around the site and adapted the positioning of mist nets to suit. Nets that would seem quite avoidable still caught birds. The following four visits saw a further 59 birds ringed including 14 Willow Warbler, 2 Chiffchaff and 4 Common Whitethroat. I also worked out when the midges started biting in the morning and by what time they would finish.

By the end of June, 20 different species had been ringed along with a further 92 individuals. The Willow Warbler total increased by another 34 birds and surely the midge season would end soon.

July arrived and the Willow Warbler total quickly increased… a further 209 birds! This mass of birds was largely within the first three weeks of the month as nests were vacated. August arrived and only 16 new birds were ringed. The final Willow Warbler to be ringed was on the 2nd of September. July was very productive and the diversity of juvenile species ringed at the site was hopefully a good indication of successful breeding in the immediate vicinity. The way the Willow Warblers rapidly disappeared was an indication that the site may not be attractive to birds on passage. This idea was reinforced by the similar post breeding departure of Blackcaps.

September saw large numbers of Meadow Pipit invade the site and good numbers of Goldcrest and Chiffchaff continued throughout the month, the latter being contrary to what I had expected considering what happened with the Willow Warblers and Blackcaps. Reed Bunting numbers gradually increased which might have indicated some sort of passage or perhaps the heather or similar plants were producing seeds resulting in an influx from the surrounding areas. Lesser Redpolls also appeared in significant numbers with some juvenile birds still having no red forehead well into the month but there was nothing to say that these birds were from the locality.

It is not possible to draw too many conclusions from one season of ringing at a site. 1070 new birds of 29 species were ringed over the five-month trial period and that alone generates enough interest for me to want to ring the site again next year and beyond. Blaenduad is a plantation; trees grow and so a CES is out of the question. Sitka Spruce are fast growing trees and the site will rapidly change and will in time become less attractive to such a diversity of birds while becoming more attractive to individual species.

Blaenduad has yielded significant numbers of both Willow Warbler and Common Whitethroat. It will be interesting to see what return rate there is to the site next spring. For Willow Warbler there could be enough individuals to create a RAS. I hadn’t considered Common Whitethroat to be a particularly common bird around northern Carmarthenshire as most hedgerows do not appear that suitable? Perhaps I haven’t got that correct or maybe the scrub at Blaenduad provides an equally good alternative.

With a significantly large catch of Willow Warblers, it has been possible to plot the wing length of adult birds and juvenile birds. The first of the graphs below shows two distinct peaks but at the same time a potential overlap between sexes. The second graph introduces first year birds.

The two peaks in the juvenile wing lengths reflect the adult peaks but offset by about -2mm. The magnitude of the right had peak in the ‘first year bird’ line is probably a bias introduced by playing sound lures (ie more males trapped). At present I don’t have enough data to look in detail at body mass comparisons against wing lengths. Many of the spring females were in various stages of egg production/laying and male birds may have been on the light side due to energies expended during territory defence. However, it has made me wonder if first year birds are forced to adopt a different autumn migration strategy if, as a result of shorter wing length, they have a higher wing loading.