Monday, 27 August 2012

Wknd 25-26 August

Large numbers of seabirds remain in the Forth, Dave mentioned "Masses of Auks, certainly in the thousands, on the sea between Gosford and Seafield" on Friday. I had estimated 850+ off Cockenzie that day, c. 60% Razorbill, many ads + young or groups of 10, 20 and even 50, some mixed with Guillemot. From the reports it seems the only counts in excess of 500 for feeding flocks in last 30 years or so were 2140+ Guillemot 19/8/04 (DA) and 580 Razorbill 29/8/07 (HEMD), both counted from Musselburgh.

This current concentration in the Forth may not be a coincidence given the recent influx of terns which presumably home in on good feeding and can rapidly move to better areas if needed? Consistent with this hypothesis there have also been great gatherings of gulls and Gannets at shoals offshore, along with Shags etc. I'm a novice at fish ID, and auks usually consume prey underwater, but in those brought up for chicks have noted what seem to be sandeels; have seen Shags/Cormorants eating pipefish, flatfish and probably sprats. One study* of Guillemot diet off western Scotland found a marked seasonal change:

"In April and June the diet was mainly or substantially composed of sandeels Ammodytidae (overwhelmingly the lesser sandeel...). In contrast, sandeels were absent in August and November. Diet was also considerably more diverse in the later part of the year, ... when various clupeids (sprats and herring) and gadids (whiting, poor cod, and cod) were the major components of the diet.

This pattern may partly explained by the biology of the prey species. Sandeels bury themselves in muddy or sandy substrates for much of the time during late summer/early autumn to late winter, and so become less available to Common Guillemots. Sprats are generally found offshore in spring and summer, becoming abundant closer to shore in late summer and autumn (Jones 1976). As a result, they become more available to Common Guillemots in later summer, at the same time that sandeels are becoming unavailable."

[Postscript: Bryan on LBN confirms the gulls and auks are indeed consuming sprats, he also comments on the "strange sound" we hear floating in from the sea of the combined begging calls of the many young auks, it is actually a magical noise and the first time I remember hearing this here!]

Other ad hoc sightings: 1260 Herring Gull (96 juv) on Seton Burn/shoals immediately offshore Friday early afternoon; 1 juv Arctic Tern on burn; 1 juv Puffin amongst 660 auks in Forth on Saturday; 23 Red-necked Grebe off Longniddry Bents on Sunday afternoon, roughly half still in summer plumage (one shown above, normally too far offshore!), 5+ more beyond Ferny Ness but poor visibility; ad Roseate Tern and ad Med Gull on rocks east of c/p 2, the latter was still there at dusk to roost (unringed); 110 Sandwich Tern in Seton roost Sunday, and a Common Sandpiper past, but no Meds :(

Only one atlas success with Woodpigeon nest found at Longniddry Bents.

Monday - still 3 Swift feeding over house amongst House Martins on a muggy still evening. 36 House Martins over the house a couple of weeks ago must have included birds from elsewhere in the village, seem to have done well this year and still entering nest on house opposite today (27 August).

* Halley et al (1995) "Seasonal and geographical variations in the diet of Common Guillemots Uria aalge off western Scotland", Seabird 17:12-20.

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