Bad parenting could give zebra finches the evolutionary edge

William Feeney, The Conversation

Species must reproduce to survive, and animals have found unique ways of achieving this. For some, including us, it seems as though producing a few offspring that require extended care is the best strategy. For others, such as many coral reef fishes, many offspring that require little care appears better suited.

Brood parasitism is among the most bizarre breeding strategies in nature. A brood parasite, such as a cuckoo, manipulates another individual into raising its young. Hosts do all they can to stop brood parasites from successfully reproducing, because they usually harm their own young. Brood parasites fight back, and the two species can become locked in a coevolutionary arms race.

Despite these troubles, not having to build a nest, incubate eggs or care for offspring allows brood parasites to produce more eggs than they would otherwise. This can make brood parasitism viable through evolutionary time.

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How tree sparrows recognize foreign eggs in their nests

Many birds have reason to worry that the eggs in their nest might not be their own: birds often deposit eggs into other nests and it is not easy for parents to tell their eggs from others. Researchers at the University of Veterinary Medicine, Vienna have discovered that tree sparrows can recognise eggs deposited by other tree sparrows but do not always reject them. The results are published in the online journal Plos One.

Building a nest, laying and incubating eggs and taking care of a hungry brood are very demanding on birds´ energy budgets, so it is obviously in their interests to ensure that the young they are caring for are their own. Brood parasitism sometimes makes this a difficult proposition: strangers – either of their own kind or of another species – might want a free ride and deposit their eggs into ready-made nests. 

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