Gas gun starts spring sprint

 

After a long cold late winter, spring finally arrived in a wave of migrants, with interesting reports of breeding birds now arriving thick and fast.  Spring also usually means a flurry of site visits for the Grumpy Ecologist and this year has been no different; from East Anglia to the Insh Marshes and across to Wales.   The Nene Washes are always a highlight in the spring.  Reports of a gas gun keeping Cambridgeshire residents awake at night were tracked down to an over enthusiastic booming Bittern in a fenland drain.  The breeding success of waders on the washes has been poor for the past three years, due variously to drought or flood.  Fingers are crossed for a good breeding season this year.  The cold and wet winter has left many wet grasslands in good condition; short swards with a lack of winter growth and brimming pools and ditches.

The trip to the Nene provided evidence of the seasonal changeover.  While 800 islandica Black-tailed Godwits huddled together around the pools, 30+ pairs of limosa noisily ‘wickered’ and chased around the fields.  Snipe chipped and drummed over a feeding flock of Dunlin, Ruff and Ringed Plover. Garganey zipped past the last few Whooper Swans.

Over at Ynys-hir, an early morning visit coincided with an arrival of Wood Warblers, trilling through the woodlands.  Pied Flycatchers and Redstarts were already in good numbers. All three species, typical of these West Atlantic Oakwoods, were seen well from the Ynys-hir canopy hide but the highlight was a Goshawk gliding and twisting through the still bare trees with its entourage of squawking crows marking its passage.  Wood Warblers have declined by 60% in a little over a decade (BBS data), and over a longer period have disappeared from many eastern and southern haunts, yet the reason for this decline is still unclear.  Potential causes include changes in woodland structure, increased predation and a phenological mis-match between egg hatch and the peak of caterpillar emergence. Studies in Wales have failed to point the finger at any of these and indeed have shown that the timing of Wood Warbler breeding can track the annual variation in caterpillar emergence.  Perhaps the answer lies in Africa.

Of crakes and cranes

Fens-bred Crane, view of the washland at Lakenheath (is that a Great White Egret?)

The success of Lakenheath Fen is remarkable. A review of this year’s figures shows two pairs of Cranes rearing one chick, five Bittern nests, 120 pairs of Bearded Tits and 13 pairs of Marsh Harrier (as well as Garganey, Golden Oriole, Spotted Crake, Nightingale and Hobby of course). Just one species, Fen Ragwort, has been re-introduced to the site since it was created (unless you include Reed). But it is not faring well, and this prompted much discussion of the pro’s and con’s of such action.

Re-introductions always seem to be controversial. Take the return of Cranes to Somerset as an example. Now that the small East Anglian population has broken out of its original Broads homeland, and increased its productivity, it is clearly 'on the move'. One key criterion for determining if a species should be re-introduced, or not, is whether it is likely to return 'under its own steam' and Cranes are highly likely to get to Somerset under the current expansion (wandering birds already have). There can be no ecological reason for re-introducing them to the south-west.

On the other hand, it is unlikely that Corncrakes will have returned naturally to the Nene Washes. Although it is great to hear multiple ‘crekking’ crakes at the Washes, the ongoing re-introduction scheme has to resolve many difficulties, not least that Corncrakes are long-distance migrants and are somewhat difficult to observe. Captive-bred Corncrake chicks have been released at the Nene Washes since 2002, with an estimated 21 ‘crekking’ males in 2010. Birds are now breeding in the wild and returning. However, the population is not considered to be self-sustaining as yet due to the low number of returning wild-bred males. The return rate of the ringed, released males is estimated to be around 20%, similar to the return rate estimated for wild Scottish chicks in their first year. Released birds have now been re-captured up to four years after their release – the longest recorded re-capture period for a UK Corncrake. So, adult winter mortality does not seem to be a problem. One potential problem is low breeding success on the Washes, possibly due to habitat issues, and this is currently being investigated.

In deciding whether the ‘driver’ for site management is the habitat or the associated species, few would disagree that overall, the habitat approach is the best. However, understanding the requirements of key species is essential, and ‘tweaking’ where necessary can enhance their fortunes. The example of the recovery of Bitterns in recent years is clear. At the Nene Washes, there are several key species, so which way do you ‘tweak’? Black-tailed Godwits must be a priority, as the site holds the majority of the UK breeding population. However, what might be seen as ideal wet grassland habitat management for the Washes and its waders, may not deliver enough ideal habitat for the Corncrake, which brings us back to a second key criterion for re-introduction schemes – is there enough suitable habitat for the species?

Crex crex

It seems bizarre to have a crekking Corncrake 2 metres from the car adjacent to a busy road. This was just one of 8 calling birds at the Nene Washes this evening. Three were clearly audible at once from the road just outside Whittlesey. With a possible 12 males back this year, the re-introduction programme is progressing but still short of the target sustainable population. I listened to one bird for 30 minutes, glimpsing its shape in the dark, as it called incessantly from the trackside grass and nettles. Earlier, a Spotted Crake had briefly ‘whipped’ in the wet sedgey fields managed specifically for it. Result!
The continuing cool weather is keeping the Snipe subdued, but the number seen clearly hinted at the importance of this site. The fields look in good condition, held back by the weather but full of waders. Around 10-15 pairs of Black-tailed Godwits revealed themselves, at least one with chicks. The supporting cast included several pairs of Wigeon, a Whooper Swan, a dozen Little Egrets, 2 Hobbies and 4 drake Garganey. The Garganey sat together on a pool by daylight but after dark made their presence felt more obviously, their rattling calls coming from all directions as they flew up and down the washes.