Role of Evolution in the Mating Behaviors of Birds: Home (or Nest) Security Assured

Since we’re on the topic of nesting, I thought I’d bring up another species which has some seriously intense nesting endeavors. Rhinoceros Hornbills are large birds which live in the tropics, and mate for life. This is most likely due to the fact that the females must invest a HUGE amount of trust in her chosen mate, as he will be the sole provider of food for both her and the chicks while they sit in their tree-hollow nest.

Male Rhinoceros Hornbill outside their chosen nest cavity.

And in case you think it’s just a matter of incubating eggs, think again. The females REALLY depend on males, because she is literally sealed inside of it. Once the birds find a mate, they begin to create a nest inside of tree hollows. Once the nest is created, both the male and female begin to form a wall across the opening out of mud, bits of food, and feces. They leave only a narrow slit in the middle, through which the males will pass food to the incubating mother. Who will remain sitting on that egg for 50 days until it hatches, then an additional 90 days thereafter before breaking out of the nest.

You can see the females beak sticking out of the opening, which will most likely be sealed further.

The chicks then re-seal the entrance themselves (with a little help from the parents) and again the process of passing food through a narrow slit begins until the chick is ready to emerge on its own. At that point it breaks free with some help from its parents.

Juvenile hornbill poking its head out of the nesting cavity.

There is absolutely no question as to the security from predators the chick and mother gain from this time intensive nesting behavior. The nest is kept clean through all this by continual removal of uneaten food and feces (when they’re not being used to re-create the nest seal). This nesting behavior must have, looking back, been able to evolve due to the presence of total monogamy in mating pairs, as no one male would be able to support 2 completely and utterly dependant families.

While incredibly interesting it is also a somewhat frightening concept to any woman when you think about being sealed into a small, dark enclosure with your child for months on end. Though you cannot doubt your safety is assured, as long as your husband comes back…