Zur Mauser des Grossgefieders beim Seeadler (Haliaeetus albicilla) in Schleswig-Holstein

Abstract

Flight feather moult of White-tailed Eagle (Haliaeetus albicilla)in Schleswig-Holstein, GermanyBetween 1955 and 2000 feathers moulted by White-tailed Eagles were collected systematically in the breeding territories in Schleswig-Holstein, Germany. 581 tail feathers and 382 primaries from a maximum of 22 nest sites (1999) and more than 300 secondaries (81 collected between 1960 and 1970) were considered. Moulting process of primaries and secondaries is serially continuous, with several moult waves proceeding simultaneously through separate moult units in each wing. Tail feathers were moulted in sequence of 1-6-3-4-2-5 and showed a predominantly transilient alternation. Although tail and flight feathers could be moulted in any month between April and October, there was a strong tendency for them to be moulted between May and August. The plumage characteristics of 18 dead eagles of known age were also examined. Up to and including the 4th moult (in the 5th calendar year), tail moult was almost complete each year. Adults generally moulted their tail feathers over a 2-year period with an annual moult rate of 53 %. Serial moult of primaries in immature eagles normally was completed within a range of 2 rarely 3 years (annual rate = 49 %). Primary moult in adults took place over 3 (occasionally 4) years. Annual rate for flight feathers of adults (in the 5th moult and later) was 46 %. In Schleswig-Holstein the annual rates for tail and flight feathers were on average higher than those in Finland and Sweden, probably because moulting season there is shorter than it is in Schleswig-Holstein because of the different amplitudes of the photo-period in the two regions on different latitudes. Moult patterns were modelled to demonstrate the influence of breeding status, weather conditions and food availability on annual rate. According to this model females showed a higher annual moult rate of primaries and tail feathers in years without breeding success. Tail and flight feathers were moulted on average 1.5 months later in years with breeding success than in years without. Sex specific differences are seen only in annual moult rate of primaries under specific conditions. Moulting activity is higher in warm and dry summers than in cold and wet summers. This was confirmed by the examination of the plumage of dead birds.

Experimental evidence that a large raptor can detect and replace heavily damaged flight feathers long before their scheduled moult dates

“…Many species of large birds (e.g. Thus, large birds that fly while moulting often carry some heavily worn feathers in their wings and tails (Struwe-Juhl & Schmidt 2003, Rohwer et al 2011. However, many other large birds must maintain the ability to fly while moulting, with the result that they use their flight feathers for two or more years before replacing them (Edelstam 1984, Pyle 2005.…”