Penguins don’t put all their eggs in one basket

Phillip Island’s little penguins – also known as fairy penguins – exercise a distinct strategy of “resource allocation” in their egg-laying practices, a new report reveals.

The birds lay two almost identical eggs but each has a different nutrient composition, the study by researchers from Spain’s Doñana National Park, Environment Canada and Phillip Island Nature Parks discovers.

Phillip Island Nature Parks writes:

It has long been understood that seabirds are sensitive to the fluctuations in the available food supply in the marine system, and they produce less eggs than other birds. Shearwaters lay only one egg, while many penguins lay two. Some species even lay one normal-sized egg and one tiny egg, as a bit of insurance in case the first egg fails.

The same considerations are behind the penguins’ strategy.

Over 12 seasons, data was gathered from the breeding population here on the Summerland Peninsula, in Victoria, Australia. The scientists measured, weighed the eggs and checked nests. Analysis of the stable isotope levels of blood and plasma samples showed that  the first egg received greater nutrient levels, using resources gained from the female’s steady increase in body weight well before egg-laying.

The second egg was formed with resources gained by the female just before laying, which resulted in significantly lower levels of nutrients. This gave the chick in the first egg a much better chance of fledging successfully, but nevertheless, provided a back-up.

This strategy was even more obvious in older penguins that had produced several clutches of eggs in previous breeding seasons.

The study published in the Journal of Experimental Marine Biology and Ecology.