Southward migration and fuel deposition of Red Knots Calidris canutus.

We compared the differences between spring and autumn in migration speed, fuelling rates and fuel loads of migrating Red Knots Calidris canutus. As a basis we used ringing data from Ottenby Bird Observatory, southeastern Sweden, collected 1948-2003, with morphometrical data from 1990-2003. Numbers ringed varied between 0 and 301 per year (average 56). Morphometrics, recoveries and recaptures of ringed birds indicated that most birds belonged to the Afro-Siberian subspecies C. c. canutus, possibly mixed with some Nearctic Red Knots C. c. islandica. Median trapping dates were 5 August (adults) and 31 August (juveniles). Mean body masses were low and almost equal for adults (111.8 g) and juveniles (111.4 g). The mean estimated fuel loads were 13-14% of lean body mass (LBM). In juveniles fuel loads increased with date. Among the few birds stopping over for longer than one day (2% of adults, 14% of juveniles), adult birds stayed on average 2.5 days and juveniles 3.4 days, with an overall average fuel deposition rate of 2.8% of LBM d-1. The autumn migration speed was estimated from ringing recoveries at 86 km d-1, which equals the speed of spring migration calculated from published information. The observed fuelling rate was as high as that of Red Knots at major spring stopover sites. We conclude that migration in autumn is as fast as in spring, although the generally small fuel loads indicate that migration is carried out in much smaller steps.

Helseth A., Lindstrom A. & Stervander M., ARDEA 93 (2): 213-224.