Saturday, 28 January 2012

Opportunistic crows

 ResearchBlogging.orgCorvids are omnivorous birds and display a very flexible and opportunistic feeding behaviour: they will exploit coastal resources when near beaches, will actively search for nests in the spring looking for eggs or chicks, will take advantage of human scraps, feed on roadkill or other carrion, or look for worms and other invertebrates on fields and woodland floor. They show a remarkable inventiveness regarding looking for food, leading in some species to an understanding of the manufacture and use of tools. Rooks are able to add stones to a beaker with a little water where food is floating until the water level rises enough for them to reach the food. Caledonian Crows craft tools - including hooks - from leaves and twigs and use then to fish out grubs from trunks. Other species, like Jays, have extraordinarily precise spatial memory, which allows them to cache food surplus for use later.
  In general, corvids are dexterous birds. They have excellent foot-beak coordination and often use their feet when feeding, to hold down a piece of food so that they can pick bits with their beaks, as the Carrion Crow above. In experimental set ups, Ravens are able to reach meat tied to a a long string by alternatively pulling with their beaks and stepping on the loops of the string with their foot.
Their catholic food preferences and ingenuity have undoubtedly allowed them to adapt to living near people, and some crows species, like the Carrion Crow are common in towns, cities and agricultural land.
 Carrion Crows and a Greater Black-Backed gull feeding on a dead seal pup and afterbirths on a Grey Seal colony
I saw this Carrion Crow flying with a Woodpigeon's egg on its beak. It landed and quickly opened it up and ate the contents 
The predated egg shell
Carrion crow searching for a nest while a blackbird gave alarm calls nearby
Crow feeding on a chick 
Rooks and Carrion Crow feeding on a beach
A short video of a pair of Carrion Crows feeding on the leaf litter

More information
Bird, C., & Emery, N. (2009). Rooks Use Stones to Raise the Water Level to Reach a Floating Worm Current Biology, 19 (16), 1410-1414 DOI: 10.1016/j.cub.2009.07.033

Hunt, G., & Gray, R. (2004). The crafting of hook tools by wild New Caledonian crows Proceedings of the Royal Society B: Biological Sciences, 271 (Suppl_3) DOI: 10.1098/rsbl.2003.0085

Heinrich, B., & Bugnyar, T. (2005). Testing Problem Solving in Ravens: String-Pulling to Reach Food Ethology, 111 (10), 962-976 DOI: 10.1111/j.1439-0310.2005.01133.x

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