In the field, bird researchers regularly encounter raptor pellets, which are regurgitated clumps of indigestible animal material such as fur, feather, and bones. However, where multiple species of similar-sized raptors occur, it can be hard to tell which species produced a pellet based on the pellet’s appearance alone. After field seasons spent on two Nova Scotian islands collecting raptor pellets as part of a study on predation on seabirds, one sample of pellets raised our eyebrows. The pellets we collected from an island known to host Great Horned Owls were small, about half the size of a computer mouse; those we collected from another island were huge — easily four times the size. We speculated about what could have disgorged such a monstrosity. Could it have been a Snowy Owl? Probably not, given the similar size of the two owls. An eagle? Seemed more likely, but how could we know for sure? Thus, we became interested in developing a way to identify bird species producing pellets based on residual environmental DNA (eDNA). We suspected DNA in pellets could come from a bird’s digestive tract cells, leaving behind a genetic signature in the field telling us “Who puked?”
Saturday, May 14, is World Migratory Bird Day! As our way of celebrating birds’ amazing migratory feats, we put together this round-up of migration-related papers published in The Wilson Journal of Ornithology last year. When you’re done exploring them, go check out the official World Migratory Bird Day website, which has lots of information and activities related to this year’s theme, the impacts of light pollution on migrating birds!
Over the course of many field seasons at a colony of several thousand Glaucous-winged Gulls at Protection Island National Wildlife Refuge, Washington, I noticed large accumulations of broken eggshell littering a few of the nesting territories. I watched the owners of these territories invade the territories of fellow residents, grab an egg, fly the egg back to their own territories, and eat the contents. Eggshell fragments from the stolen eggs accumulated on the territories of these egg cannibals.
Bird banders take standard measurements on all birds they process as they build their datasets, some of which require banders to use their breath to blow gently to part a bird’s feathers. One of the most universal of these measurements is an inspection of the fat layer visible under the skin, which gives information about things like migratory readiness and refueling performance. Depending on the season, banders may also need to part feathers to check for breeding condition (whether the bird has a brood patch or cloacal protuberance), the level of skull development (which aids in ageing), and any sign of molt activity.