Brent Goose Breeding Success
This autumn (2005), the arrival of Brent Goose seemed to be a couple of weeks later than expected and the reason why may now be clear. This year seems to have been a bumper breeding season for the birds and it is conceivable that the presence of so many young birds may have slowed down the migrating parties. The Brent Goose that spend the winter on the south coast breed on the Siberian tundra around the Taymyr Peninsular, so conditions during the Arctic summer must have been extremely favourable.
It wasn't until mid-October that reasonable numbers arrived on Stanpit, but it quickly became apparent that the percentage of young birds was much higher than normal. One could normally expect perhaps 10-15% of a winter gaggle to be young birds, but this season figures of up to 40% are being recorded. An apparent family party of two adults and 5 young has also been observed.
A family of four - November 2005 Stephen North
Identification of young birds is fairly straightforward, with the most obvious fieldmarks being the pale tipped wing coverts, which show as 3 or 4 diagonal bars on the folded wing. The photograph below illustrates this perfectly.
Youngster on left and adult on right - November 2005 Alan Hayden
While a ratio of 40% is being regularly recorded in Christchurch, this is in a sample of only 100 or 200 birds. The main south coast sites are actually turning in figures of around 30% on sample sizes of greater than 2000, so this is likely to be a more accurate figure.
|Langstone Harbour:||c30% of 6095 birds|
|Portsmouth Harbour:||28.6% of 297 birds|
|Keyhaven:||33.4% of 2139 birds|
Jason Crook, Ornithological Consultant, Langstone Harbour, where many thousands of Brent Goose winter, considers this to be the best year since 1991, a period that saw a 31% ratio. Although 1999 was also high with around 24%. Jason also writes. "It is also only the third time since 1991 that annual productivity has clearly exceeded the (estimated) annual rate of mortality. Hopefully it will go some way to halt their downward trend in numbers and re-structure an otherwise ageing population."
Although, during the second half of December, the winter population at Stanpit fell from a peak of 216 in November to around 100 or so, the ratio of young has not been affected and remains around 40-45%. It will be interesting to continue to monitor the presence of young birds through the remainder of the winter. If you are counting Brent Goose in the harbour, please do try to make a note of the respective numbers of adults and young.
Thanks to Jason Crook, Brian Fellows and Bob Chapman for the data from other sites.
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