Black-and-White Owls

During my peregrinations in Tikal National Park (Guatemala), I was fortunate enough to spend a good deal of time studying a beautiful and little-known species, the Black-and-White Owl (Strix nigrolineata). In fact, my colleagues (Craig Flatten and Normandy Bonilla) and I were the first to document a nest of this species. Each nest (we eventually found four) was an epiphyte (that is, either a bromeliad or orchid) high in a tree, and all nest trees were in or near bajas (the seasonally flooded lowland forests). On those epiphytes, only a single egg was laid, and to my knowledge this remains the only owl species documented to have such a low reproductive effort.

A number of other interesting natural history facts came out of that study. These owls eat lots of insects, especially the large scarab beetles abundant in those forests. But the mammalian component of their diet is almost exclusively bats, and we believe that their large home range size (relative to other owls of their size, and as we determined through radio-telemetry) was required in order to encompass a sufficient number of the fruit trees most attractive to a variety of bats. Another anecdotal observation was that the one pair we observed in three consecutive seasons exhibited astonishing regularity in their nesting--they laid their single egg on the same date (or within a day either way) each of those years.

In the photo above, you can observe the size difference between the male and female. As in most owls, it's the female that is larger. Since in most other families of birds it is the male that is larger (if any size difference exists), the situation in owls (and other birds of prey) is termed "reversed sexual size dimorphism." In this tropical species--and the other one that we studied (and which I'll post about some other time)--this size difference is greater than almost any species from temperate or boreal zones to the north. This finding, in turn, is contrary to the predictions of many of the theories attempting to explain the adaptive advantage of reversed sexual size dimorphism in owls.