Sunday, 26 April 2015

Tawny Frogmouths in their winter roosts

A Tawny Frogmouth roost-tree in open woodland
It's now late autumn and migrant birds such as the yellow-faced honeyeaters are flying over the house and general area on their annual migration to the northern and coastal forests. While other birds like the tawny frogmouths are settling down in the local woods for the winter. The frogmouths stay in their breeding territories over the winter, probably because they are a valuable resource and worth defending. And in the bird world, occupiers usually win over any intruder. So to keep warm in the cooler months, during the day they settle on a favourite perch where they can catch the winter sun.

A Tawny Frogmouth sits quietly in her roost

I know most of the local birds' perches and  most days they will be in one of perhaps two or three, for they have sussed that those branches offer shelter from predators and exposure to the sun. Exposure to the sun is important to them, for the morning sun warms them up. Also, these birds can go into torpor for part of the day to conserve energy. And that is not their only two strategies for enduring the winter, they also build up body fat. The female I found dead last week was carrying 88 grams of fat, approximately 16% of her weight, and her stomach was full of beetles and large moths. The contents formed 8% of her weight. She had been feeding hard catching the last of the autumn insects before the lean times ahead in the cold nights. (I acknowledge Gil Pfitzner of CSIRO for this information as he was the one who prepared her skin for the national collection and took these measurements).

This bird is several years old - I know her by the pattern of her bib,
and she knows me because she has seen me so often over the years
The more we look at birds, or any other wildlife, the more we can learn about how well adapted each species is for its own niche. As for the tawny frogmouths, they have so many adaptations, they continue to fascinate me. No doubt they will have more that I don't know of - just what is the purpose of those bristles above their eyes and bill?

Here she has closed her eyelids, almost. She is still peeping through a slit and even if she closed her eyes further, she could watch me through tiny gaps between her eyelids. For her eyelids have rippled edges allowing her to see out, but not for a predator to see her eyes. Frogmouths are very well adapted for concealment, right down to their eyelids, and surveillance at the same time. Eyes can be a big betrayer of camouflage. This bird hasn't gone into full defensive pose as she is familiar with me and does not feel under threat. She is just basking in the sun - with a little caution.

1 comment:

  1. " I know her by the pattern of her bib" - does this mean the patterning is maintained from moult to moult? And how much is the patterning perturbed by the lie of the feathers between preenings? I've often wondered about these questions in relation to other birds as well where there is less patterning but perhaps some potentially identifying plumage characteristics.