It is often the case that sexual dimorphism in
animals leaves the males more colourful and with extra appendages that are used
to impress females. However this is not the case in socially monogamous birds, such
as the Blue-footed Booby, Sula nebouxii.
Both male and female Blue-footed Booby’s both have
brightly coloured blue feet used during courtship. The reasons behind the
females having ornamental structures like the males have seldom been documented.
In this case it is in the interest of both the females and males to have nice
blue feet.
A study has found that the bluer and brighter a
females feet, the more attractive she is to the males. Through an experiment of
temporarily changing females feet to a duller shade of blue, scientists found
that they received less intra- and extrapair courtship than the control
females. They concluded that the blue colour of the feet is favoured by sexual
selection through male preference.
In a similar study, the opposite was tested.
Scientists found that the brightness of the males feet colour was related to
the overall health of the bird. When deprived of food for 48hrs, the blue
colour became duller as an indication of its ill health. This study also found
that this had an influence on how much reproductive investment the female put
in. After the first egg was laid, the
male responsible was taken and his feet were temporarily modified to appear
duller and less attractive. In response females decreased the size of their
second egg as their partner appeared to be in ill condition. They concluded
that female Blue-footed Booby’s continually evaluate the health of their
partners to determine the amount of their reproductive investment.
References
Torres
R & Velando A. (2005). Male preference for female foot colour in the
socially monogamous blue-footed booby, Sula
nebouxii. Animal Behaviour, 69(1), 59-65.
Velando
A, Beamonte-Barrientos R & Torres R. (2006). Pigment-based skin colour in
the blue-footed booby: an honest signal of current condition used by females to
adjust reproductive investment. Oecologia, 149(3), 535-542.
This was very interesting! I had heard about the blue-footed booby before and they are interesting. I knew that their blue foots were correlated to their health, but I didn't realize it was associated with reproduction this much.
ReplyDeleteAnother awesome video! Blue-footed booby birds are quite fascinating. I love the courtship displays both sexes show! What kind of foods do these birds eat? Do you know how the pigmentation of the feet is made/works? Great blog!
ReplyDeleteHey Tasmin. As far as I can tell they just eat fish. For the study they were fed (or not fed) Atlantic Bonito. The colours in their feet are a result of carotenoids being deposited in the integuments and that these are derived from the animals diet as they cannot manufacture them themselves. As some of the carotenoids are antioxidants then I guess it makes sense that a dull foot colour would signal ill health.
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