Update from the field site at Stora Karlsö!
Stora Karlsö is home to several species of seabirds, chief amongst them common murres (Uria aalge) and razorbills (Alca torda). While extensive research and much data has been collected on the murres, the razorbills are less well studied. This field season Tom Evans and I set out to find out more about the foraging ecology of this enigmatic alcid. The deployment of both GPS and time-depth recorder (TDR) loggers on individuals not only allows us to see where and when the birds forage but also (through dive depth, wet/dry, and temperature data) allows us to construct time budgets. The expectation is that we will be able to say something about the ranges, duration, and dimension of their foraging trips. Not only does this increase information on the biology of the species, it can be compared with sympatrically breeding species and enhance our understanding of the Baltic ecosystem.
Left: Last time together for the time-depth recorders. Right: A GPS logger sealed with heat-shrink plastic, ready for deployment.
Part of the reason that razorbills are less extensively studied than other auks such as murres, is that they appear to be extremely sensitive to handling. At our colony we managed to catch individuals by hand at the nest (usually in a crevice or under a boulder), but the real challenge is re-capturing them. While our experience was no different than at other colonies, we now should have enough data from several years to perform analysis and begin to paint a picture of razorbill movement and foraging ecology in the Baltic.
|Razorbill registers its rage at researchers|
Preliminarily, it looks like the razorbills forage between 10-50km in every direction around Stora Karlsö (concentrating on the South) and dive up to 25m below the sea surface to catch sprat (Sprattus sprattus) and herring (Clupea harengus). Most foraging activity seems to take place during the evening and early morning. The common murres travel a similar distance but almost exclusively to the west with dive depths up to 80m. It is to be expected that closely-related sympatrically breeding seabirds with the same diet would seek to minimize interspecific competition by segregating in at least one aspect of their overlapping niche.
|Example of a 4-day GPS track of a breeding razorbill on Stora Karlsö 2015.|
And with one final cute picture, Tom and I bid farewell for this field season!
3-day old razorbill chick vocalizing on the Auk Lab at S. Karlsö.