Clutch Size Research Reveals Interesting New Insight

Anyone with an interest in birds may have spent at least a little time wondering why it is that some bird species lay only one egg while others lay up to ten eggs. The question certainly seems to have been plaguing biologists who have gone out of their way to come up with an answer.

The number of eggs laid by a bird is called the ‘clutch size‘. In a bid to understand why the clutch size of certain birds differ so much from other birds, biologists combined data on the clutch sizes of a whopping 5 290 species of birds from around the globe. The information covered not only the bird species and clutch size, but the biology of the bird and the environment specific to each of the species. The results of their findings were recently published in the journal PLos Biology.

The clutch sizes of both birds and reptiles has long been a subject of interest for biologists. Generally speaking, it seems that species which are short-lived or which have a low survival rate tend to lay more eggs, while those that live longer or have a higher survival rate will lay fewer eggs and spend more time nurturing their offspring. However what happens when one bird lays just one egg and another bird of a similar species lays ten? Why are there such huge discrepancies? It seems that some of the answers lie in the variations in a particular species’ environment, nutrition, health and risk of predation. The study was also able to make use of manuscripts dating back hundreds of years so as to gain insight into how environmental changes may have affected species over the years. The results show that increased environmental variation has caused birds to lay larger and larger clutches. Nest shape is another factor. Birds nesting in more open nests are more at risk from predators and so less eggs so that less eggs are at risk. In contrast, a cavity nester, such as a woodpecker, will have larger clutches since they are better protected. Season and location are another two factors that play a role. It seems that the research has helped the team to accomplish one of their main goals – that of accurately predicting the average clutch size for types of birds living and breeding in certain environments. This information could greatly aid conservation efforts and will no doubt prove to be most helpful in the future.