Well it's almost that time of year now when the Whimbrel return!
Eight years ago, during 2004, the Lower Derwent Valley Whimbrel project started, it was based around the spring passage staging site at Wheldrake Ings. The site has been known as a spring staging site for the species since the early 1980's with a peak of up to 100-150 birds around the first week in May, building up from the first bird in mid April to the last bird in mid May. Birds appear on the LDV NNR at dusk to roost, but prior to 2004 we had no idea about anything else that these birds were up to. Whilst there had been quite a bit of research on the small British breeding population of Whimbrel in Northern Scotland over the years, there has been very little work on spring staging sites such as these except some work in the 1970's on a roost that no longer exists on Steart Island, Somerset.
Whimbrel - Wheldrake Ings - 09/05/05
Below are some of the questions we wanted to try and answer:
- Where do the birds go during the day
- How many birds are involved in the spring staging site
- How much turnover is there and how long do individual birds spend at the roost
- How important are such spring staging sites to those birds that migrate using this strategy
- How much weight do the birds gain
- What are the energetics involved
- Which races/breeding populations do birds using this site belong to
In an attempt to answer some of these questions, since 2004 a total of 100 Whimbrel have been caught and colour-ringed at the Lower Derwent Valley NNR spring roost. Several birds have been radio-tracked and four have been fitted with satellite trackers.
Whimbrel with colour-rings - 27/04/07
Whimbrel fitted with radio tag - 25/04/05
Whimbrel fitted with satellite tag - 27/04/07
From this work we have now established that:
- Birds tend to feed locally to the roost site, often within 2-3 km, on semi-improved grassland but perhaps (and most significantly) on one specific soil type.
- Individual birds tend to spend 8-10 days at the roost, at which time they almost double their body weight (arriving at about 300-350g and leaving 550-600g - 8 days later!).
- They are very site specific - often returning year after year to the exact same roost site and the exact same feeding fields nearby. Not only that but they appear to do so with amazing regularity, often turning up on the same date every year - keep watching our blog updates over the coming weeks to follow this years Whimbrel story. The first birds of the spring roost have usually (for the last five years) appeared on 16th April (next Monday), although Dave had what was almost certainly 4 passage birds at the site at dawn on Tuesday of last week (11th).
- Birds appear at the roost (best viewed from Swantail Hide) around sunset (7.45 to 8.25 pm) - smaller numbers of birds may be found during the day when they move onto Wheldrake or Bank Island (occasionally North Duffield) for a drink and wash, although this is more frequent towards the end of the passage period.
Please do keep an eye out and let us have ANY colour-ringed records, don't assume we have seen the birds or someone else has reported them - its usually not the case!
Colour-ringed Whimbrel - Wheldrake - 09/05/05
