The penguins are now on their way back home to the colony after having had a
restful few weeks off the coast of Brazil. Back home in the colony the weather
is still very cold, but hopefully it should start getting a bit warmer soon.
Here in the southern hemisphere we are now into our spring, and the days are
gradually getting longer. In the winter the days are very short here, and it
gets dark by about 5pm, but now the days are getting longer and it now gets dark
at about 7pm. In mid-summer it does not get dark until about 11pm, and even then
it never gets really dark.
The colony is virtually deserted during the winter. There are no penguins at
all, just seagulls and sealions. I attach a photo of the sealions which live
nearby. The sealions live here all the year round, and do not migrate like the
penguins. The penguins escape the short gloomy days by spending the winter off
the coast of Brazil, but now they are on their way back home.
Life was very easy for Promises off the coast of Brazil. Adult penguins very
rarely go hungry because it is easy for penguins to catch enough food to feed
themselves. Adult penguins don’t need a lot of food, and with no responsibilities
they are free to travel wherever they want in search of the best fish. However
that all changes when they get back home to the colony, and are forced to fish
within easy reach of their nest.
It takes several weeks for Promises to travel the 5000 kilometres from Brazil
back to the colony. It is about the same distance as New York to London – a long
journey for a small penguin. We expect them to arrive back home later this month.
Most of the nests have been damaged and eroded by the wind and rain during the
winter, so the first task for Promises will be to rebuild the nest and make it
suitable for the eggs. Once the nest is repaired the female penguins will lay
two eggs. The eggs are very large compared to the size of the penguin, so they
are laid one egg at a time. The second egg is laid about four days after the
Penguins never lay more than two eggs, and some species only lay one. Larger
penguins, like Emperor and King penguins only lay one egg, because the chicks
grow so large that the parents would not be able to catch enough food to feed
more than one chick. Most other penguins lay two eggs, but some have strategies
that mimic one egg.
Rockhopper and Macaroni penguins lay two eggs, but the eggs are different sizes.
One egg is a normal size for a penguin, whilst the other egg is very small and
does not hatch. The theory is that Rockhopper and Macaroni penguins find it better
to raise one healthy chick, rather than try sharing food between two chicks and
end up with two weak chicks. So over millions of years natural selection has
favoured pairs that had one infertile egg, to the point where the second egg
has now become so small that it is no longer viable. This is a strategy of ‘slow
but sure’ in which food resources are used to ensure the survival of one healthy
Other penguins, like Gentoo penguins, lay two equally sized eggs a few days apart,
but despite the fact that the eggs are laid a few days apart, the chicks hatch
together. As a result both chicks are born equal in size and both have the same
chance to compete for food with their sibling. Both chicks squabble to get fed
by the parents, but since both are the same size, both chicks get equal amounts
of food. This is an opportunistic strategy that allows these penguins to increase
their population rapidly during good years, but it can occasionally lead to total
breeding failure in bad years.
Magellanic penguins, such as Promises, also lay their two eggs a few days apart,
but unlike Gentoo penguins, the chicks also hatch a few days apart. This is a
more flexible breeding strategy which lies between the two extremes. This breeding
strategy produces one chick that is smaller than the other at the time of birth,
so the smaller chick only gets fed when food is plentiful, and the larger sibling
has been fed. This reduces the chances of total breeding failure if food is in
short supply, by ensuring one healthy chick instead of two weak ones.
However that doesn’t mean that you should worry about Promises in the future.
Here in our colony food is in good supply, even during difficult years. When
food is in good supply, both chicks get well fed and grow quickly. Within just
two weeks both chicks increase their weight 5 times and the tiny size difference
at birth disappears completely, resulting in two healthy chicks of equal size.
We expect Promises to arrive home at the nest later this month. The egg-laying
should then begin in late October or in early November. As soon as the eggs have
been laid I will send you a new photo of Promises in the nest.
Best wishes, Mike