Let's talk about birds

It’s that most wonderful time of year when the word “nutcracker” enters into conversations again, and mostly because of the title character in a fanciful holiday ballet. In the story, the Nutcracker is not a bird, but there are birds that are nutcrackers.



In fact, there are two birds, both members of the crow family, named nutcracker. The Clark’s nutcracker is found throughout the high mountains of western North America; the spotted nutcracker lives in the mountains of Eurasia, including the Himalayas. Both of these birds feed primarily on pine “nuts,” the hard seeds found inside pine cones. Their long, strong bills enable them to extract the seeds from in between the stiff scales of pine cones.

Other avian nutcrackers are the macaws, large members of the parrot family. The birds’ name, macaw, comes from an indigenous South American word for palm nut. Macaws are among the few animals capable of cracking very hard-shelled palm nuts to feed on the high-energy oily nut meats inside. Their formidable nut-cracking ability is thanks to their very tall, stout, hooked beaks and their strong jaw muscles, which enable them to exert a maximum bite force of up to 2,000 pounds per square inch — 10 times that of a human and twice that of a snapping turtle. Only crocodiles can bite as hard as a macaw, but they don’t like nuts.

At this time of year, people often put out bowls of nuts in the shell for holiday gatherings. It is nearly impossible for anybody to crack them with their bare hands or teeth, though, so if we want the nuts to be more than just decoration, we will make sure there is a mechanical nut cracker and nut pick nearby. But, if our guests were large macaws, they could easily help themselves, exerting the bite force needed for cracking even the hardest nutshell, and then using their nimble feet and pointed beak to deftly extract every little bit of nut meat.

From starving chicks come fat birds

Dr Andrews, of the Newcastle University Centre for Behaviour and Evolution said: "Building up body fat reserves as a safeguard against times of potential future famine is an evolved survival mechanism. What we have shown is that birds that had struggled against larger brothers or sisters for food early on were keener on finding food and tended to overeat when they became adults".



To ensure that some birds were disadvantaged by experiencing greater competition, smaller starling chicks were placed in a brood with significantly larger hatchlings. These chicks had to work harder than their siblings to be fed, spending more energy on calling to their parents for food and jostling to the best feeding position.

Dr Andrews explains: "The smallest chicks were bottom of the heap and had a tougher time because they would have had to beg hardest for food."
These disadvantaged chicks were compared with birds that were placed in broods with significantly smaller chicks. After ten days, disadvantaged and advantaged chicks all lived together in relative luxury so that it was only their 'chickhoods' that differed.

Birds that had a tougher start spent more time searching for hidden crumbs despite the ready availability of alternative sources and ate more of the freely available crumb when they accessed it. The birds that had an easier start, having been the largest in the nest, opted instead to take the easy pickings in moderation.
The scientists suspect that the birds with a tougher start, the disadvantaged starlings, were behaving as if they were worried food might run out suggesting that they have a 'memory of hunger' from when they were small which drives them to overeat when presented with freely available food.