Why don't these penguin species have three Eggs?
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by
gardenmaeve
moderator
"...seems to have 3 chicks. by asb2718 July 31 2016 7:48 AM
In the nest under discussion in this image, there seem to be two smaller chicks and a larger chick. Perhaps two chicks appear to be three or the larger chick is from a nearby nest. We don't know just looking at this image. Great close observation by @asb2718 !
Sometimes on Penguin Watch we think we see nests with three eggs or three chicks. While it is possible to observe such anomalies in the wild, it is a rare occurrence. That's a good thing, and here's why:
Timing is everything with penguins. It has been observed that second-try eggs (after the first nest in a season has failed), and eggs laid by first brood females tend to be smaller due to the relatively poor condition of the female. It takes at least a year of good feeding to eat enough to be in top condition for nesting. When food supplies are diminished nesting can be delayed or even skipped for a season.
When a female penguin is nesting as she is laying her two eggs, she is also fasting. As each of the two eggs is formed, she goes without food until the second egg is safely in the nest and her mate takes over the first extended brood turn. She has exhausted her reserves and must go feed. If she delays, she'll need to remain at sea longer to replenish her stored fat, which delays her return and makes it likely the male will be forced to abandon the nest and eggs so he can go feed. There is neither time within the very short nesting season, nor body stores for a third egg from that female.
Secondly, penguin brood patches are sized for one or two eggs. It would be very difficult to keep all three eggs under the brood patch safe from extreme weather and predatory birds. Think of the skuas and sheathbills and gulls trying to annoy the adults into exposing their eggs and young chicks. A third chick would cause all the chicks to be more vulnerable.
Third, studies have shown that a mated male and female catch and feed the same amount of food for one chick as they do for two. Think about that- it means one chick is fed what two chicks are usually fed. Imagine trying to feed three! When, rarely, three eggs are seen it is because two females have paired with the male at the nest site. I've found no observations of both females remaining at the nest, which would leave one male and one female trying to brood and hatch and feed all three chicks. Success is highly unlikely.
One chick gets more food, two chicks increase the chance of at least one growing to adulthood, three chicks are likely to threaten the well-being and survival of all three chicks while making it very difficult for adults to remain in viable physical condition. The success of next year's eggs will be influenced by the parents' condition in the current season.
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