Blue-headed Wagtail (Motacilla flava) Science Article 3
Timing of pre-migratory fattening among Yellow Wagtails Motacilla flava wintering in Nigeria pre-1980 is compared with that in the period 2004-2006 to determine whether this has been affected by trends towards earlier spring phenology in Europe over the same period. Wagtails wintering in northern Nigeria showed later fattening, in central Nigeria similar timing, and in southern Nigeria earlier fattening, than comparable pre-1980 populations. Later fattening in the north may be related to environmental degradation and difficulties faced by such populations in advancing migration date because of the proximity of the moulting period. Consistency of timing in central Nigeria may be related to the regular arrival of drought-breaking rain at this latitude around the start of April, and earlier fattening in the southerly winterers may reflect a general lack of constraint for such populations, which gain weight in wet season conditions, several weeks after the end of moult. Since southern winterers breed furthest north, advancement of spring arrival time should therefore be more pronounced among populations breeding in northern Europe.
Christopher Paul Bell, J Ornithol (2007) 148 (Suppl 2):S495-S499