Due to reproductive isolation, a new species of weaver bird is evolving. Is it likely to use a social or solitary nesting strategy?

Question

A.  It depends on whether it lives in the forest or the open savanna.
B.  It depends on whether it lives in near water or near the desert.
C.  It depends on how many similar species it is competing with.
D.  It depends on how many eggs it lays.

Answer 1

A.  It depends on whether it lives in the forest or the open savanna.


African weaver birds, which construct nests from vegetation, provide an excellent example of the relationship between ecology and social organization. Their roughly 90 species can be divided according to the type of social group they form. One group  of  species  lives  in  the  forest  and  builds  camouflaged, solitary nests. Males and females are monogamous; they forage for insects to feed their young. The second group of species nests in colonies in trees on the savanna. They are polygynous and feed in flocks on seeds.  The  feeding  and  nesting  habits  of  these  two  groups  of species are correlated with their mating systems. In the forest, insects are hard to find, and both parents must cooperate in feeding the young. The camouflaged nests do not call the attention of predators to their brood. On the open savanna, building a  hidden  nest  is  not  an  option.  Rather,  savanna-dwelling weaver birds protect their young from predators by nesting in trees, which are not very abundant. This shortage of safe nest sites means that birds must nest together in colonies. Because seeds  occur  abundantly,  a  female  can  acquire  all  the  food needed  to  rear  young  without  a  male’s  help.  The  male,  free from the duties of parenting, spends his time courting many females—a polygynous mating system.