Furthermore, juveniles and subadults may

benefit from automimicry because they resemble adults in appearance. “
“Plumage constitutes a significant component of the somatic investment of birds. A detailed investigation of feathers and moult can help to uncover trade-offs involved in somatic investment decisions, the sources of some of the costs birds have to pay and the potential fitness consequences. We used micro-computed tomography imaging to study the second moment of area, a structural parameter that is one determinant of bending stiffness and the cortex volume of flight feather shafts of two sister taxa, the willow warbler Phylloscopus trochilus, a migratory species with two annual moults, and the chiffchaff Phylloscopus collybita, a migrant with one annual post-nuptial moult. Juvenile and adult willow warbler and chiffchaff feathers, all grown on the breeding Trametinib grounds, are structurally very similar to each other.

Willow warbler feathers grown during moult on the wintering grounds, however, have a significantly higher second moment of area and a significantly larger cortex volume than all the other feather types. We discuss the possibility that the seasonal variability of willow warbler Pirfenidone concentration feathers may be an adaptive structural reflection of a moult–migration strategy that has allowed this species to occupy large breeding and wintering ranges. Feathers make up c. 30% of the protein dry mass of a bird’s body (Murphy, 1996) and thus constitute a significant share of the total somatic investment. A detailed investigation of feathers and moult can therefore help to reveal the trade offs involved in somatic investment decisions, the sources of some of the costs birds have to pay during their annual cycle and the associated fitness consequences.

Plumage can reveal such costs and trade-offs in at least two ways. (1) Limited resources are invested in competing activities. Somatic costs are paid when resources devoted to, for example, reproduction are traded-off against demands of self-maintenance, that is, in the case of feathers moult. Thus, breeding–moult or moult–migration overlap MCE公司 may lead to lower energetic investment in feathers and hence, lower quality feathers. (2) High work load can directly affect the degradation of feathers through increased exposure to UV-B radiation (Bergman, 1982; Borgudd, 2003) and keratin-degrading bacteria (Burtt & Ichida, 1999), higher contact rates with abrasive vegetation and more cycles of bending during flapping flight (Weber et al., 2005). Recently, a number of mechanisms underlying trade-offs involved in moult have been investigated in some detail. Dawson et al.