Got the not-so blues

For blue-footed boobies, foot colour is a big deal -- such a big deal, in fact, that females lose their enthusiasm for laying healthy eggs when their mates feet lose their blue brilliance.

Blue-footed boobies, who live on the Galapagos Islands and the eastern Pacific coastline, tend to lead monogamous lifestyles. Each year, females usually lay 2 eggs, of equal size, about 4 days apart. Roxana Torres and colleagues let females lay the first egg, and then used a non-toxic marker to make their partners' feet look duller, suggesting the partners were unhealthy. Consequently, they found, second eggs were layed later and were considerably smaller than expected.

This finding meets with predictions: if females want the best for their babies, then they should vary how much energy they invest into producing offspring depending on how well they suspect their offspring will survive. If the males are unhealthy -- or in the case of blue-footed boobies, are less blue -- then the offspring may have a harder time surviving. Moreover, if the female blue-footed boobies invest more attention to the older egg, then at least one offspring is likely to survive. Perhaps there is something to putting all your eggs in one basket after all.

Presumably, the fact that the second egg is smaller than the first and comes later than expected (making it altogether less likely to succeed) is not the consequence of a decision on the part of the lady bird, but is rather an involuntary response. Do such responses occur in humans too? Is it possible that women coupled with unhealthy (or even seemingly unhealthy) men don't invest as much in as-yet unborn offspring as they could -- unconsciously of course?