SEASONAL CHANGES IN BODY‐WEIGHT OF OYSTERCATCHERS HAEMATOPUS OSTRALEGUS

• Published in: Ibis
• Main Author: Dare, P. J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1977
• Subjects: Iceland
• Online Access: http://dx.doi.org/10.1111/j.1474-919x.1977.tb02056.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1474-919X.1977.tb02056.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1474-919X.1977.tb02056.x

Summary The body‐weights of Oystercatchers Haematopus ostralegus wintering in Morecambe Bay, north‐west England, showed marked seasonal changes between late summer and late winter, with considerable differences apparent between adult and immature birds. An attempt is made to relate these changes to recorded seasonal variations in prey biomass and to the annual cycles of breeding, moult and migration of the Oystercatcher. The mean weight of females invariably exceeded the mean weight of males in samples collected on the same dates, regardless of age. Adults returned from northern breeding areas in very lean condition, with mean weights ranging from 526 g in males to 540 g in females. Mean weight then increased progressively, due mainly to fat deposition, to a peak in March (up to 662 g in males and 675 g in females) around the time of their main departures for breeding. Heaviest birds then exceeded 800 g. Birds migrating to Iceland in spring would need to be of above average weight in March to make the shortest crossing (850 km, 13 h), via Scotland, while Oystercatchers of 700 g and over could probably make a direct flight (1500 km, 25 h) from Morecambe Bay in favourable weather. Breeding weights of British Oystercatchers were similar to those of post‐breeders returning to Morecambe Bay in late August. The mean weights of first‐year Oystercatchers arriving in August were very low, 449 g in males and 478 g in females. Their weights, and those of second‐ and third‐year immatures, then rose rapidly in autumn, with some fat deposition, and reached mean values ranging between 551 g (males) and 597 g (females) by November‐December. Mean weight then fell by 10–17% from December to March returning close to or below the September levels, whereas adults gained a further 6% during these winter months. Summer and autumn weight gains, and the major moult of adults and older immatures, occurred when the biomass of their two staple mollusc preys, Mytilus edulis (mussel) and Cardium edule (cockle), was maximal. Winter loss in ...