Frogmouth Fledglings

two weeks and two months out of their nests



This pair of frogmouth fledglings have been out of their nest for two weeks, so as they were in the nest for four weeks, they are now six weeks old.

It is now January and most of the young frogmouths have left their nests, all those in my study areas have. When they do so, they become more obvious to people out walking and I am frequently asked how I can tell the age of the fledglings. So, here is a brief guide to the telling young and old frogmouths apart, using birds of known age.


This is the same pair seen in their family group. Mum is up top and dad is next to the chicks on the far right. He is slightly larger than the adult female and she has red on her wing coverts. Although the fledglings are well feathered, they are still only about half the adult size and weight.


The chick on the left is probably a male because it has grey coverts on its wings, the other one, in the middle, is probably a female as it has red/pink colouring on its coverts. Both can fly quite easily between trees as their wing and tail feathers are well developed, although their tails are not fully grown. Both chicks still have much fluffy down feathers around their heads and bellies, this is probably the best indicator that they are still young birds. The adults' body feathers lie smoothly against their bodies, except one stray feather on the male's upper wing which it is in the process of moulting out.


In a neighbouring territory, the fledglings have now been out of their nest for two months (so they are three months old) and they look much more like adult birds. In the above photo, the bird in the fore is a fledgling, that behind is its father. The bulges of stray downy feathers on the young bird's flanks catch the light as they stick up from the body. Those on the adult male lie flat and the under-tail coverts are longer and well streaked.


As most people view frogmouths from below, it is perhaps best to focus on what can be seen from below to guide aging these birds. And tails are the most obvious feature from that angle. The adult's tail on the left is long and smoothly edged. The youngster's tail on the right is shorter and ragged. The individual feathers are smooth, but they are of different lengths as they grow. When scrutinised, the young birds tail feathers look very smooth-tipped, the adult's tail fathers are usually frayed and chipped with wear as the bird has had most of them for a year or more. They will have pairs of fresher feathers within the mix as new ones are grown in replacement of those moulted out, but it is difficult to see that detail in the field.

In another month, they will be almost indistinguishable, but there are ways to tell.

Metamorphosing into chrysalides 


A Tailed Emperor Charaxes sempronius Caterpillar curls up in preparation for metamorphosing into a chrysalis - the final stage before it then metamorphoses into an adult butterfly. (See the previous posts for further details on my watch of these caterpillars)


I counted seven caterpillars on the host food plant, a Persian Silk Tree, and as I watching them over the days, I noticed that the first had disappeared a few days ago. So I traced the branches, looking for any wanderers. I first found one crawling swiftly along a branch, heading away from the leaves where it had grown, and probably where its egg had been laid. I measured its pace and was surprised that it was travelling at 20 m per hour. Not bad for a 6 cm long caterpillar. This is probably the most vulnerable stage in its life as it was exposed, with no camouflage while on the bare branches and predatory birds could easily spot it if I could. I found three, and one was still feeding, so where were the other three. Had they found a secluded spot or had they been eaten?


Once they had selected a suitable spot to settle, they fixed themselves by the a specialised hooked organ, called a cremaster at their tail end, to a silk pad they prepare on a branch. Then they hung down on it, and kept wriggling in a curled position to begin with.

Hours later, they let themselves go and hung down straight. This is when they begin to metamorphose.


However - all three of the ones I could find changed into their chrysalides overnight. I set up a slow-motion camera on two of them, but that only worked in daylight. By morning the chrysalides were almost fully formed. The shot above was taken late in the evening. The shot below, of the same animal, was taken next morning. The leaves of the tree close up at night and open by day.


The chrysalis forms inside the old skin of the caterpillar, and when ready, it breaks through the back of the skin. The old skin is then wriggled up to the tail end where it dries and is shaken off. All is complete. I shall now wait about two weeks and try to capture the emergence of one of the butterflies from a chrysalis in slow-motion time-lapse.