NOORDHUIS R (1989) Patterns of primary moult: ecophysiological adaptations. LIMOSA 62 (1): 35-45.

This review paper summarizes the various patterns of primary moult and discusses their function. Some new ideas concerning the functional aspects of moult patterns are presented. In general, replacement of flight feathers proceeds in a regular sequence. Within a species or species group all individuals basically follow the same pattern, but between species or species groups considerable differences can exist, especially in the sequence of replacement of the secondaries. Patterns of moult are now believed to be highly adaptive. Flight feathers will be replaced in a sequence that gives the growing feathers maximal protection and affects the power of flight as little as possible. Primary moult usually follows an outward or descendant order; a small number of species show (partly) an inward or ascendant moult. It is suggested that descendant replacement is the easiest way to prevent a growing primary from being bent upward by lift forces during flight. In strictly ascendant moulting species a shedded primary will leave the still growing fresh primary underneath unprotected, as a result of which it possibly can be damaged at its vulnerable base. This problem can be solved by moulting odd and even primaries in separate series, as occurs in the partly alternating (transilient) ascendant moult of cuckoos and parrots. Secondaries are believed to be less affected by aerodynamic forces operating during flight, due to their smaller size and denser spacing. The timing and sequence of their replacement (in most cases largely ascendant) is likely to be influenced by the aerodymanic and energetic demands of the primary moult. The duration of replacement of all flight feathers is linked to the wing loading of the species concerned. In general, larger birds have larger wiJ;1g-loadings and thus must replace their flight feathers more slowly if the ability of flight is not to be lost. This results in stepwise moult (StafJelmauser) in the largest species, where a new moult cycle starts before the preceding one has been completed. A number of species which are less dependent on flight (mainly aquatic, often diving species) shed their flight feathers simultaneously, shortening the period of inconvenience to only a few weeks. In many cases large migrants are not able to complete primary moult within the period between the breeding season and the autumn migration. In most of these cases moult is interrupted just prior to migration (suspended moult). Since the time available between breeding and migration changes with latitude, considerable differences in timing and duration of moult can occur between populations ofone species. The highly adaptive flexibility of the process of feather replacement is again evident in this case.

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