Birds Prefer Acacias over Oaks
Cattle pastures in the tropics are surprisingly attractive to birds. The scattered oak and acacia trees provide insect food and cover despite the grazing underneath.
The acacia trees are the star of the show. Birds, particularly migratory birds, are much more often found in the acacia trees than the oak trees. The attractiveness of the acacias is easy to explain. There are three to four times as many insects in them than there are on oak trees.
Why are there more insects in acacias? It appears that acacias have geared their defenses against leaf-munching mammals. They have thorny spines and chemicals in their leaves that are distasteful to large herbivores. Oaks, on the other hand, have a variety of chemical defenses designed to thwart insects.
Oak trees do have more large insects than acacias. Resident birds, which are quite a bit larger than migratory birds and have broods to feed, favor large insects. Many resident birds will nest throughout the year.
For migratory birds, a lack of competition and abundant food make the acacia a favored tree.
This article summarizes the information in this scientific paper:
Greenberg, Russell S. and Bichier, Peter 2005. Determinants of tree species preference of birds in oak-acacia woodlands of Central America. Journal of Tropical Ecology, 21: 57-66.