Sunday, 12 February 2012

Ringing again at Manor Farm Country Park

The weather conditions this morning looked ideal for ringing so I headed to Manor Farm for my first ringing session for a while. Once again it was freezing cold, and as I drove to the farm the temperature gauge in my car registered minus five!!! I am so glad I hadn't set the nets the night before as they would have been frozen solid. 

I was hoping that the cold weather would have brought in loads of thrushes, but in fact the frozen conditions had probably had the opposite effect and forced birds to move on. There were a handful of Redwing and Fieldfare present, single Grey and Pied Wagtails and not much else. But having made the effort I persevered and eventually ended with a total of 33 birds, including Blue Tit, Dunnock, Robin, Song Thrush, House Sparrow, Goldfinch and Greenfinch. The low number of birds around gave me the opportunity to concentrate on those that were caught, and it was just as well as in the end some interesting subjects were captured.

The first interesting bird was a Robin. The moult strategy in this species is typical of many European passerines, with adults undergoing a complete moult post breeding, whereas juveniles undergo a partial post juvenile moult. It is therefore usually possible to see an obvious break in the greater coverts between retained juvenile and moulted adult feathers in juvenile birds. But it is important not to be fooled by the variation in thorns present on the greater coverts (see below), which could be considered to be indicative of a moult limit. The example below seems to show an obvious break, but examining the ground colour of the feathers and the length and shape tells a different story.

Adult Robin

Referring to other features also pointed to something different; the broad and rounded tail feathers indicated an adult bird, and the all dark inside of the upper mandible the same. Luckily, this bird was a re-trap that had originally been ringed in November 2010 as a juvenile, and therefore it was possible to correctly age it as an adult...a very interesting lesson for the trainees present!

Adult Robin

Another species that always promotes discussion when trying to age it is the Dunnock, and today there was no shortage of them to discuss. According to Svensson (1992)(Identification Guide to European Passerines), ageing is possible in the autumn by way of eye colour and the paleness of the base of the lower mandible, whereas Jenni and Winkler (1988) (Moult and Ageing of European Passerines) suggest that the prominence and colour shade of light tips to the greater coverts and inner tertials is useful. Svensson is extremely cautious of this feature suggesting that the variation in different individuals is such that this feature should only be used by experts in the species. Two of the birds captured today illustrated perfectly why Svensson is skeptical of this feature.

Juvenile Dunnock Wing

This species again has a moult strategy which involves adults undergoing a complete post breeding moult, whereas juveniles undergo a partial juvenile moult, and therefore it may be possible to see a break in the greater coverts. The image above illustrates strongly pale tipped greater coverts, but what appears to be an obvious break where two darker and smaller tipped inner greater coverts are present. In addition the tail (below) is pointed and is heavily abraded, again  indicating a juvenile bird.

Juvenile Dunnock Tail

By contrast, the image below illustrates greater coverts that are not pale tipped and with no obvious break to indicate a moult limit...

Juvenile Dunnock Wing

                                               ......whereas the tail of this bird shows an obvious fault bar, a feature typical of a juvenile bird, and again the tail feathers are pointed and abraded.

Juvenile Dunnock Tail

As it happens both of these birds were again re-traps that were originally ringed as juveniles in the summer of 2011, and therefore are both first winter birds.

Adult Blue Tit

The session ended with another interesting record, this time a longevity record for the site, in the form of an adult Blue Tit. This bird was initially ringed on 11th July 2006, 5 years and 216 days previously; surprisingly the national longevity record for this species is 9 years, 9 months and 2 amazing age for such a small bird!

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