After having had several successful catches in the vicinity of the Discovery Hut, four of us ventured down to Colyford Common to ring in the 'crop field', which hasn't been used for crops in quite some time & is now actually a scrubby field. We set six nets, and had a hot, tiring but successful morning, catching 55 birds of 16 species.
As is usual for this time of the year, the bulk of the catch consisted of juvenile birds, and most of the few adults we did catch were undergoing a main moult including wings & tail (moult code M). Much discussion was had during the morning regarding the age & moult code of various birds.
All Blackcaps in their original nest-grown plumage have brown heads, and only gain their black caps (males) & chestnut caps (females) during their post-juvenile moult. It can sometimes be difficult to determine if the brown cap is that of a bird in completely juvenile plumage before moulting has begun (age code 3J, moult code J), or a female.
The bird shown below was determined to be a 3J J ie hatched this year and as yet to start its post-juvenile moult. The very pointed tail, with growth bars that lined up (not really visible in the photo) strongly suggest this is a young bird, and the bare belly is very pink & smooth, again suggesting a juvenile bird.
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| Blackcap with no active moult....female or 3J J? |
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| Completely bare belly....3J J or adult with brood patch? |
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| Very pointed tail...a juvenile feature (although there is a lot of overlap) |
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| Female Blackcap (age code 3J, moult code P) |
We caught 13 House Sparrows, a bird that we seldom catch around the Discovery Hut. House Sparrows are one of only a few species in the UK in which both the adults & juveniles both undergo a full moult as a post-breeding or post-juvenile moult respectively. This can make aging tricky as the usual premise, that a bird undergoing a main moult of wings & tail is an adult, doesn't apply. However, looking at the wear of the feathers & the presence of a brood patch can help. An adult House Sparrow would have grown its wing feathers last year & they would therefore be more worn & tatty than a bird hatched this year which has only had a few months of wear. Of the 13 House Sparrows caught, only one was an adult.
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| Adult female House Sparrow (age code 4) |
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| Wing of adult House Sparrow |
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| Feathering-over brood patch of adult House Sparrow |
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| Juvenile House Sparrow (age code 3) |
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| Wing of juvenile House Sparrow showing less worn old Primaries |
This Blackbird was undergoing its post-juvenile moult:
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| Juvenile Blackbird |
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| Growing feathers are black, showing that this is a male. |
This Blue Tit was also undergoing its post-juvenile moult:
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| 3J P Blue Tit (juvenile undergoing post-juvenile moult) |
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| Moult contrast between replaced Greater Coverts & juvenile Primary Coverts |
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| Moult limit in tail between old greenish juvenile feathers & new blue central feathers |
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| Juvenile Garden Warbler (age code 3) |
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| The Team |
Ringed | |
Blackbird | 2 |
Blackcap | 2 |
Blue Tit | 6 |
Cetti’s Warbler | 1 |
Chiffchaff | 3 |
Dunnock | 5 |
Garden Warbler | 1 |
Goldfinch | 2 |
Great Tit | 3 |
Greenfinch | 1 |
House Sparrow | 13 |
Reed Bunting | 1 |
Reed Warbler | 3 |
Robin | 1 |
WillowWarbler | 7 |
Wren | 4 |
55 |
