Wednesday, 22 April 2009

The Straits of Beddington

Something rather strange is happening with Common Buzzards and the farm. I saw 15 today with 6 in the air at one time. In the last three days alone there have been probably 40+ birds. To put this in perspective in 2006 there were only 36 records all year, in 1996 only two records all year and between 1990 and the beginning of time there were only five records. April is prime time for Buzzards at Beddington with 23% of records from this month (another 23% in September meaning that half the sightings are in April and September) suggesting a passage of birds this time of year. Interestingly the first ever record was on April 13th 1946.
There have also been five Red Kites over the last three days.
This kind of raptor migration is rather interesting as it is not really being seen anywhere else in our immediate region. We have been discussing what is going on and have come up with the following reasons to explain it:
1) A passage of long range migrants moving north- following the Wandle valley and drawn towards Beddington by the circling large gulls over the tip (however not all birds are going north)
2) Local birds from the surrounding hinterland on exploration movements for breeding areas- moving around in somewhat large circular movements creating repeat counts
3) Local birds checking out the rubbish tip- attracted by the carrion but being driven off by crows and gulls- perhaps they neuro-automatically keep coming back being attracted in by the circling large gulls in the thermals and/or the scent of decaying organic matter.
4) Because of the recession there are daily groups of birders (everyday is a Sunday nowadays) watching the skies increasing the incidence of sightings further. Also we are a further 50 meters higher with a panoramic view- thanks to the completed landfill mounds- (maybe these mounds generate thermals?).
5) The large gulls and crow population on the farm act as an 'alarm' system by mobbing the raptors- elsewhere this factor is absent reducing the likelihood of detecting a high passing raptor
6) Graham from Holmethorpe informs us that Buzzards visible over the North Downs tend to gain a great height before heading north and tend to be invisible when they cross the valley at Holemthorpe- thus supporting the idea that Buzzards are migrating at height across a broad front but are only visible at Beddington becuase something attracts them lower.
Link to Graham's blog on searching for high raptors:


Chris Dunn said...

Re: Reason 4)
Wouldn't be interesting to see if there were similar upswings in records during the recessions of 1980-82 and 1991-92. Maybe there's a hitherto overlooked correlation between 'firsts' and recessions! Get those old reports out ;-)

Peter Alfrey said...

That would be a great paper- 'The correlation between the economic cycle, unemployment and vagrants':-)

Steve Gale said...

When I was a regular at Beddington (1974 - 1987) large raptors were very rare indeed. We didn't have the observer coverage that you do today, but the settled team of birders that were around then wouldn't have missed buzzards, harriers or kites. Of course, back then there was no tip, lake or large concentration of corvids and gulls. The Brian Milne,Bob Scott and Ken Osborne eras were also virtually raptorless if my memory is correct.

Peter Alfrey said...

Absolutely. The increase in records is not totally due to observer coverage (although birding method may contribute to some degree). Raptor populations are increasing and maybe a migration route has formed becuase of habitat changes (lake, tip etc):

Pre 1990 records of Honey Buzzard (One), Red Kite (Two), Marsh Harrier (Six), Buzzard (Five) and Osprey (one).

1990-2006 records of Honey Buzzard (17), Red Kite (17), Marsh Harrier (56), Buzzard (116) and Osprey (19).

It is very interesting and is a very welcomed development. Brilliant to see.