Wednesday, May 7, 2014

The First Females

Several females have now made it back.  There are currently at least 3, but there could be more waiting in the wings.  Only one of these females has previously bred at the field site.  In general, fewer known females return to the field site each year.  In comparison, a larger chunk of males are previously banded and the first males to make it back from migration are general ones that have previously bred at Lux, possibly because they know where they're going.  Of the 11 males that have been identified so far, 9 have bred in previous years.  Offspring that return are also more likely to be males.

In mammals, females are more likely to stay in their natal groups while males are usually the sex that disperses.  Birds show the reverse pattern, with males being more likely to stay in their natal areas and females disperse.  These patterns, known as sex-biased dispersal, serve a useful biological purpose.  If one sex disperses farther than the other, it's less likely that siblings or other close relatives will meet as breeding adults and try to mate.  This reduces inbreeding and it's genetic consequences.  The patterns I've been seeing with the house wrens might be a reflection of this wider behavioral tendency.

First female caught this season at territory A7.  She was actually born at Lux Arbor in 2012 in a different portion of the study site.  She appears to have paired with the male at A7 and sings in response to simulated intruders, despite the fact they haven't started a nest yet.  

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