Hey there, Z.I. fans! I have decided to study in Puerto Rico for a while, but never fear — I am working hard to bring you a special three-month Puerto Rican edition of “Zoological Investigations”! It seems logical to write the first article about one of the birds I’ve come here to see, the smooth-billed ani (Crotophaga ani).
Smooth-billed anis are resident breeders in southern Florida, the Caribbean, Central and South America. Smooth-billed anis are members of the cuckoo family, Cuculidae. They share the sub-family Crotophaginae with three other species: groove-billed anis (C. sulcirostris), greater anis (C. major) and guira cuckoos (Guira guira).
Most cuckoos are brood parasites, birds that don’t bother to build a nest and raise their own young, but instead lay eggs in the nest of a host species. Brood parasites rely on host parents to raise their chicks, either because the host species cannot recognize the parasitic eggs and chicks as different from their own, or because the parasite hangs around for a while to monitor, threaten and terrorize the hosts. In the latter case, if the host rejects the parasitic egg, the real parent will trash the host nest, forcing the host to start a brand new nest. This can cause the host to lose an entire breeding season, meaning it will produce no offspring of its own; in this case the host often tolerates the parasitic eggs and raises the young.
The crotophagids are not brood parasites. Some species form simple monogamous pairs, build a nest and raise their young just like any Good Book-abiding Christian would. Smooth-billed anis, however, are more like communists.
C. ani come together in groups of socially monogamous pairs of anywhere from two to 17 individuals. This upper range is an odd number because unpaired individuals sometimes join a group and help at the nest, or try to sneak in extra-pair copulations. Adulterers!
During the breeding season, which in Puerto Rico coincides with the wet season and greatest invertebrate (food) abundance, from about September to January, ani groups choose a nest tree, commonly Mesquite (Prosopis pallida) or Rólon (Pithecellobium dulce), and help to build a communal nest of branches and twigs lined with green leaves. All females of a group lay their eggs in the communal nest and everybody helps to incubate the eggs and later to feed and raise the chicks. While at first glance this system appears peaceful and utopian, in fact it is quite the opposite.
Since the ani groups are formed from monogamous pairs, each pair and indeed each individual is clandestinely trying to maximize its own reproductive output. When a female comes to lay her eggs in the nest, she will assess the other eggs present and often will bury all the eggs she finds before laying her own. Anis also toss eggs directly out of the nest; both activities kill the other birds’ eggs.
What is going on here? What is the benefit of living in a group if you are going to fight one another and kill each others’ babies? How can you stand to sit next to your tree-mate and preen them after they have just destroyed your eggs? How do the anis know when to draw the line, leave everyone’s eggs alone, and just all incubate the eggs to make some babies hatch already? What are the advantages to communal living in this system that allow this behaviour to be maintained?
These are just a few of the questions being studied in smooth-billed anis today by professor James S. Quinn and some of his students at McMaster University in Hamilton, Ontario. This fall, Quinn and myself are attempting to test whether smooth-billed anis recognize and associate egg colour with egg age, as newly laid eggs are white while older eggs are blue.
Yesterday, I shook hands with a cactus.
Stay tuned for the next “Zoological Investigations” article, which will feature another exciting Puerto Rican species!