When analyzing eye size in different bird species in relation to their lifestyle as brood parasites, hosts or non-host birds, Ausprey found that brood parasites had larger eyes than host birds – beyond the difference expected as a result of their larger body size – and that birds with larger eyes relative to their overall body mass were less likely to have their nests parasitized. “By collecting more light, large eyes improve a bird’s visual acuity, its ability to resolve an image in dim conditions and at long distances.” “Having larger eyes is similar to having a bigger camera lens,” Ausprey said. In a recently published study, for example, he found that birds with larger eyes were more likely to forage on insects or other prey that would require farsightedness, while those with smaller eyes tended to eat nectar or seeds that could be detected up close. Ausprey and his colleagues digitized Ritland’s data and explored the implications of eye size on a variety of traits.
To study the relationship between eye size and brood parasitism, the researchers turned to data collected in the 1970s by Stanley Ritland, a student at the University of Chicago who measured the eyeballs of more than 4,000 species of birds in museum collections. “What we did not know before this study was whether their eyes are adapted to egg rejection.” They also can see into the ultraviolet range,” Hauber said. They have four color receptors instead of our three. “Birds have much better vision overall than we do as humans. The failure of some host birds to recognize foreign eggs in their own nests is somewhat perplexing, said Mark Hauber, a professor of evolution, ecology and behavior at the University of Illinois Urbana-Champaign, who co-led the new research with Ian Ausprey, a recent doctoral graduate at the University of Florida department of biology and the Florida Museum of Natural History. This allows them to devote their parenting efforts solely to their own offspring. These birds will pierce or grasp the egg and eject it, abandon the parasitized nest or – in some cases – enshrine the parasite’s egg by building a new nest on top of the old one. Some bird species targeted by brood parasites can recognize a foreign egg. If host birds fail to recognize eggs that are not their own, brood parasites can produce more offspring than would be possible if they simply raised their own. The hosts’ own young suffer as a result of competition with the alien birds. Eye size likely plays a role in the contest between avian brood parasites – birds that lay their eggs in the nests of other species – and their hosts, who sometimes detect the foreign eggs and eject or abandon them, scientists report in the journal Biology Letters.īrood parasites succeed by offloading the job of parenting to other species. Image: The common cuckoo lays its eggs in the nests of other bird species, burdening these hosts with the task of raising its young.
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