Division of labor

In many bird species, males set up and defend breeding territories, and females build the nest, lay the eggs and incubate them — a division of labor that ensures the best possible outcome for their offspring.  In other species, both parents feed their chicks; in still others, just the female, or just the male takes responsibility for providing food to the incubating female as well as the chicks.  The latter is the case for the ospreys I have been observing at a local marsh.

osprey-at-the-nest-

Male osprey bringing a delicious fish to his mate who is incubating her eggs.  The fish are always headless — I wonder if he eats the head?  Does it have some particular nutritional value for him?

Males bring the sticks to the nest, the females arrange them, forming a large nest cup surrounded by a foot or two of sticks and even leafy material around the outside.  Female osprey perform almost all of the incubation, sitting on those 2-3 precious eggs for more than a month! (32-42 days), rarely getting a chance to fly off and spread their wings.  The male brings her food, but she might also get some of her daily energy requirement by metabolizing some of the protein in her inactive flight muscles.  (More about the implications of this in the next post.)

osprey and chicks-

While the chicks are young, they must still be brooded in the cold, shaded in the heat, and need their food diced up for them.

The female remains on the nest to protect them for at least another month, although the male might share some of this time with her.  Meanwhile, he is the chief food provider, bringing as much as 6 pounds of fish to his brood and his mate on a daily basis.

osprey with fish-

This fish still has its head…

Once the chicks are feathered out, grown almost to the size of the adults, and able to stand up and move around in the nest, the female takes some time off, and leaves their care to the male. Now he has to not only feed them, but guard them from potential marauding eagles or owls that might like a tasty osprey chick for dinner.  (An account of this predatory behavior is described here.)

osprey-

Dad is on duty, watching over the nest from a tree nearby.

At about two months of age, having exercised their wing muscles, and practiced “helicoptering” (hovering over the nest), osprey chicks may try a test flight to a nearby tree, where they hang out, still insisting that dad come feed them.

osprey nest and fledglings

The scene at the osprey nest currently — one chick still on the nest, and one in a nearby tree (highlighted brown and white spot). Dad was busy looking for fish, mom was never seen — this is when the chicks are vulnerable to predation.

osprey chick-

This chick was making some incessant begging calls, as the male flew by the nest in search of a fish.

The male flew right in, dropped and the fish, and the chick immediately started picking at it.  Notice the way it stretches out its wings to hide its food from view -- typical raptor feeding behavior.

The male flew right in, dropped the fish, and the chick immediately started picking at it.  So, now they are apparently able to feed themselves. Notice the way the youngster stretches out its wings to hide its food from view — typical raptor feeding behavior.

osprey nest, adult and fledgling-

Now the other chick is making begging calls — dad has to go and get a fish for that chick.

osprey-

Osprey are busy parents during June and July in Minnesota.  This female has finished molting, replacing worn and broken feathers, damaged during her long stint on the nest. Now she must exercise those atrophied wing muscles to get ready for migration.

2 thoughts on “Division of labor

    • Are these local nests? I hear that chicks have now fledged in many of the nests in the Twin Cities…look for them in trees nearby. They will be here for a few more weeks learning to fish.

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