Question

Brown headed cowbird babies are raised by birds that are not their biological parents and are, in fact, different species than them. They beg for food with a huge gaping mouth, and the adoptive parents feed more food to the cowbird baby than to their own genetic offspring. We wonder: why do they do this? Which of the following represents an ultimate explanation of this behavioral interaction?

Answer 1

Adoptive bird parents feed cowbird chicks more due to the innate behavior of responding to exaggerated begging signals, such as gaping mouths, which triggers a strong feeding response. This form of brood parasitism takes advantage of the host parents' instincts to feed their young and increase overall reproductive success.

Step-by-step explanation:

Brown-headed cowbirds demonstrate a behavior known as brood parasitism, where they lay their eggs in the nests of birds of different species. This leads to the adoptive parents raising cowbird chicks alongside their own. The ultimate explanation for why adoptive bird parents might feed a cowbird chick more than their own offspring relates to the instincts and innate behaviors of feeding. Cowbird chicks typically have large gaping mouths and engage in exaggerated begging behaviors, which can instinctively trigger a stronger feeding response from the adoptive parents. These responses are innate, just like the behavior of mother gulls feeding their chicks when they peck at a red spot on the beak, as seen in Figure 8.2.3. Additionally, protecting and raising offspring, demonstrated by various behaviors in different species such as the killdeer's distraction technique, is essential to the survival of the species, as noted in the discussion about caring for the young.

From an ultimate perspective, the behaviors of the adoptive parents can be seen as a result of natural selection favoring traits that increase the chances of survival of offspring – even if the offspring are not their own genetically. As such, the exaggerated begging of cowbird chicks exploits these parental instincts. Over time, the host parents' ability to distinguish between their chicks and brood parasites may have been insufficiently advantageous to evolve, possibly because brood parasitism was not frequent enough to impact the reproductive success of the host species. Meanwhile, for cowbirds, brood parasitism frees them from the duties of raising their young, allowing them to reproduce more often.