08/09/2018
The
further away from the equator, the quicker tempo animals' lives tend to follow.
Birds at more northerly latitudes mature faster, start reproducing younger and
don't live as long, probably as a way of dealing with seasonal variation in
resources. A new study from The Auk: Ornithological Advances shows
for the first time that this pattern also plays out in feather development,
with northern birds completing their annual moult faster to keep up with the
demands of life far from the tropics.
Louisiana
State University's Ryan Terrill looked at museum specimens of four species with
ranges that span a wide swathe of latitude in both the Northern and Southern
Hemispheres. Slight differences in feather growth between day and night during
a bird's annual moult produce visible pairs of light-coloured bars, each pair
representing 24 hours' growth. Terrill could determine the rates at which
individual feathers grew by measuring their spacing. He found that in all four
species, individuals collected at higher latitudes had grown their feathers
faster.
Terrill
sees two potential explanations for this pattern, which aren't mutually
exclusive. First, where the availability of food changes with the seasons,
birds may need to moult faster so that they have the necessary resources.
Second, because birds at higher latitudes tend to be more invested in producing
offspring than in extending their own survival, faster production of
lower-quality feathers may be an acceptable trade-off.
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