Saturday, 22 September 2012

Black-head squeeze continues

The remarkable increase of breeding Black-headed Gulls in the Lee Valley has continued this year, nearly all of them nesting on rafts provided for Common Terns.  This year’s total amounted to 107 pairs spread across four sites, with good numbers of young birds fledged.   By contrast, the Common Terns have had a very poor year.  The total of 52 pairs is the lowest in the valley for some 30 years.  Not only that, but productivity has been equally poor.  But are these two stories linked?

Terns in general appear to have had a very mixed year, both between and within species.  The poor summer, with a high proportion of windy days preventing fishing and the downpours chilling eggs and chicks, has been a major problem.  In the valley, many terns failed to settle until very late this year, with limited success.  In general, productivity at inland colonies is frequently better than the average.  Common Terns nesting on freshwater sites have been shown to make shorter feeding forays than coastal birds, allowing for better colony protection as birds are away from the nest less. 

Although the Black-headed Gull is over ten times as numerous as the Common Tern as a breeding bird, both species have shown an interesting similarity in trend in distribution and abundance in recent decades.  Although there have been declines in the north and west of the UK, increases have taken place in inland areas of southern England, much linked to the spread of flooded gravel pits in river valleys.  In recent years, Black-headed Gulls have spread rapidly along the Thames valleys and its tributaries, in many cases nesting on rafts provided for Common Terns.  The reasons for the declines in the north are unclear but an increase in predation, particularly by Mink, and unfavourable land-use changes have been suggested as the cause.  

With the Black-heads increasing rapidly in recent years, the general feeling is that the terns are being squeezed out.  Despite this, all the local colonies had available space on the rafts.  In recent years, the delaying of the positioning of rafts has shown some limited benefits for the later nesting terns.  Perhaps the time has come to vary the design of the standard tern raft to better accommodate both species as they seem to have subtle differences in nest location.  Around the world you can find examples of a very different approach.  Look at the 22,000 m2 floating island designed for Caspian Terns in Oregon, USA for example (below).  Some trials next summer at a number of sites may begin to show the way.

Sunday, 9 September 2012

Rush conundrum


Phew!  A twitchable Baillon’s arrives at Rainham Marsh in a perfect viewing position.  Not unexpected, given the influx this summer (but I would guess this may be a Dutch bred bird). However, a relief after the necessary news blackout of territorial birds. At least the North London birding press should be able to report this one correctly without relying on various blogs and adding a dollop of speculation.  Journalists, pah!

I joined the assembled crowds at dawn on Saturday and marvelled at the ability of the little critter to find this particular little patch of suitable rushy habitat.  Having received some photos of Baillon’s Crake habitat in The Netherlands back in June, I noted the swamps of Flowering Rush and Bur-reed and initially thought they had sent me a picture of Rainham as a joke.  A quick e-mail to Rainham ensured they were crake surveying at night but to no avail.  Anyway, this shortish, open-structured wet vegetation appears to be just what they like.  Okay, I saw the ‘89 Sunderland bird but that clearly had a dodgy radar.

Now the conundrum.  The marvellously crakey rush habitat at Rainham does not favour the usual fare of waders and gulls.  In fact, management is being undertaken to significantly reduce the amount of rushy edges to the pools in favour of muddy margins suitable for White-tailed Plovers and the like.  Okay, the rushy habitat could be shunted away into a corner away from prime hide viewing, but then who would see the next crake?  A conundrum to be pondered and not to be rushed.  What would you do?
Above - Flowering Rush and botanists closely studying it.  Below - Baillon's Crake habitat in The Netherlands (Ruud van Beusekom) and at Rainham, snap!