Evidence of polygamy in the Tawny Frogmouth

An adult male Tawny Frogmouth sits second from the right between five fledglings. 

I recently found a brood of five fledgling Tawny Frogmouths Podargus strigoides that were being attended by one adult male and two adult females. The birds were first observed at the nest on 14 November 2024 and the birds were seen on several subsequent visits to the nest area (up to 29 Dec 2024). The nesting area was in dry sclerophyll forest on Black Mountain in the Australian Capital Territory (ACT). As far as I can determine, this is the first record of a brood of five Tawny Frogmouths.

The two adult female Tawny Frogmouths, perched on the same branch on 29 November. Female A is at the top of the branch, female B lower down on the same branch.

The observations were made while monitoring nests and broods as part of a long term study of Tawny Frogmouth breeding ecology (18 years). Six trios of breeding Tawny Frogmouths have been recorded previously in the study, although none with more than three fledglings (1x1, 2x2, 2x3, 1x failed). These records have not been published, I had planned to publish them in more context when all the data are collected. However, due to the interest in this new record, I decided to write a brief report that was published in the local bird club journal, Canberra Bird Notes 49(2) see here.  It is not known if one or both females laid the eggs in the nest in this instance. Given that frogmouths usually lay 1-3 eggs it appears that both females in this instance laid eggs and this was a polygamous relationship consisting of a breeding trio. In the article, I pondered whether this was the first record of a brood of five or of polygyny in any frogmouth species, or polygyny in any of the Caprimulgiformes. The records for the frogmouths seem to be the first of their kind, although there have been previous records of polygyny in nightjar species. 

          

Above left: Female A. She is overall more grey than female B. There is less rufous colouring around the face and less prominent streaks on the breast. 

Above right: Female B. She is overall more rufous, especially on the wing coverts and around the face. Her breast is more obviously streaked.

The breeding biology of the Caprimulgiformes is poorly known and they are generally thought to be monogamous (Cleere 2010). Polygyny has seemingly only been documented in four species, the Standard-winged Nightjar Macrodipteryx longipennis (Holyoak 2001), the Pennant-winged Nightjar M. vexillarius (Jackson 2004), the White-winged Nightjar Caprimulgus candicans (Pople 2003), and European Nightjar Caprimulgus europaeus (Odder Jensen 2013, Evens et al, 2024). The males of the first two species have exaggerated plumage differences from the females, such as elongated feathers, which they use for display in leks and so are considered to be polygynous. Male White-winged Nightjar also display in dispersed (exploded) leks (Frith 2024) and have been proved to mate with more than one female in a study using VHF radio tracking. The European Nightjar has only recently been proved to be polygynous in studies using GPS-telemetry.

A full report will be published on the breeding ecology of Tawny Frogmouths in the ACT when the study is completed and a separate publication will discuss polygyny in the species and other Caprimulgiformes.

The adult male frogmouth sits with four of the fledglings behind him, on 29 December. The other fledgling was with female A and female B was on a branch above them.

Cleere, N. & Nurney, D. (1998). Nightjars. – Pica Press, Sussex

Evens, R., Lathouwers, M., Creemers, J., Ulenaers, E., Eens, M., & Kempenaers, B. (2024). A Case of Facultative Polygyny in an Enigmatic Monogamous Species, the European Nightjar (Caprimulgus europaeus). Ecology and Evolution, 14(10): e70366.

Frith, C. B. (2024). Use and definitions of the terms arena, lek and court in describing avian courtship sites. Ibis.

Holyoak, D.T. (2001): Nightjars and their allies: The Caprimulgiformes. – Oxford University Press

Odder Jensen, N. (2013). A Case of Polyterritorial Polygyny in European Nightjar Caprimulgus europaeus. Dansk Ornitologisk Forenings Tidsskrift 107: 239–244.

Jackson, H. D. (2004). Courtship displays of the Pennant-winged Nightjar, Semeiophorus vexillarius. Ostrich 75: 1-4.

Pople, R. G. (2003). The ecology and conservation of the white-winged nightjar Caprimulgus candicans [Apollo - University of Cambridge Repository]. https://doi.org/10.17863/CAM.16393

 

Frogmouth chick rescue 

Following on from the last post on how frogmouth fledglings are vulnerable to becoming grounded and dying in tall grass, I found such a bird yesterday. I was monitoring the progress of some of my study birds and was expecting them to have fledged the night before. When I went to the nest site, I saw that they had indeed fledged. The nest was empty and the parents were perched on a branch in a neighbouring tree with one chick beside them. That raised alarm in me as I knew there had been two chicks ready to fledge only a few days prior. Usually, when there are two fledglings and they have split up, mum will sit beside one chick and dad with the other. But, there were both parents with only one chick. Where was the other. Unlike in the previous post, when one chick had probably grounded in wet tall grass and succumbed to hypothermia, in this case the grass was tall, but dry, so I reckoned that if a chick had grounded in the tall grass in the previous night, it could still be alive. So I searched for it, very, very slowly, and careful to look down into the grass before I moved my feet. I didn't want to step on it.

As the adults tend to sit with a chick each if they are separated, I thought the missing chick might be directly below where the rest of the family were perched. And yes, it was, and it was alive.

The grass was more than knee deep and thick, so the bird could not climb up, fly up on its weak wings, or even struggle through the dense growth. It would have died if I had not found it.

The fledgling had fluttered about twenty metres before grounding, not far from the nest branch which can be seen in the background.

And yes the chick was not only alive but perky, giving a ferocious sounding growl as I bent down to pick it up. It opened its big mouth wide and flashed its wings to appear powerful and more fearsome than it really was. 

Of course, once the fledgling began to react, its parenst both reacted to my interference. They both hooted aggressively and swooped over me. That is a big commitment for frogmouths as they only fly in daylight under extreme circumstances of danger. Here dad sits above me, watching my every move as I carefully picked up his still-dependent offspring.

The fledgling looked bigger than it actually was. Most of its growth so far had been in bone and feather development. There were only weak muscles beneath all that fluff.

I popped the bird onto a dead branch in the shade below where the family were perched. This is the best thing to do if anyone finds a frogmouth chick on the ground. The adults will be close by watching. Just because we might not see any adults, that does not mean there are none there. These are frogmouths, masters of disguise and they can be very difficult to see when perched motionless in a tree, which is what they do most the day.

The fledgling soon settled on its new perch and as I walked away it faded deeper and deeper into the mix of branches. I reckon it would have been safe and a parent would soon fly down to perch next to it for the rest of the day to defend it.

But how many other fledglings have died this year in the wet and windy we have had.

Tawny Frogmouth chicks:

vulnerable when fledging

Tawny Frogmouth chicks are now fledging in Canberra, and unfortunately there have been some heavy and prolonged rainstorms at the same time. This has caused some chicks to be grounded when they fly between trees and if they stay there, they can be vulnerable to predators such as cats and foxes - both introduced pest species. Every year, people find such grounded fledgling frogmouths and are tempted to take them home to save them. After all, they are the most Instagrammable bird in the world, with their fluffiness, big forward facing eyes and apparent sad mouth-line. See the scientific paper below that describes the relevant study:

Thommes, K. & Havn-Leichsenring, G. (2021). What Instagram can teach us about bird photography and color preferences. i-Perception, 12: 20416695211003585.

This chick was low to the ground, on a fallen branch, but its sibling had disappeared. It probably died during the heavy rain in the previous night after grounding in the tall grass and weeds that are growing all through the woods this year due to the rain. The birds cannot climb up out of tall wet grass and can quickly succumb to exposure. 

It is difficult for me to walk through the tall grass and weeds. It must be deadly for frogmouth fledglings. And I have seen this happen before.

Nevertheless, please do not pick these birds up and take them home. They are not pets. The best thing to do is place them on a nearby branch, up off the ground, as high as possible and walk away quietly, without drawing attention of any predatory birds that might be watching, such as ravens or currawongs. The chick's parents will be watching them, like the adult pair in the background of this picture.

And the chicks have a very good threat display, if they are attacked. Although even that pose makes them very Instagrammable. 

 A New Spring

By our calendar it is still winter in Canberra, but the wildlife have considered it spring for a couple of weeks now and they are showing the signs.

This Shingleback was sunning itself in a wood the other day, the first of two I saw that day and the fourth so far this Spring. They all lay perfectly motionless with their bodies spread wide to absorb the sun's heat.

This Golden-headed Cisticola popped up out of the grass as I passed through an ungrazed paddock overgrown with weeds. He gave a few alarm calls at my presence then dropped back down and disappeared into the grsss.

And the first Tawny Frogmouths have laid their eggs. The males are now incubating all day, for the next four weeks, remaining still to avoid detection by predators, such as Brown Goshawks, a pair of which were displaying over this birds nest wood. 

The frogmouths share incubation during the night, but during the day, this bird's partner will remain similarly still in her nearby roost all day, watching for predators - and watching me as I pass by.

Last frogmouth chicks of the year 

A very large Tawny Frogmouth chick lies in its nest next to its father. The nest was set on the end of a broken branch. The chick is almost fully feathered, enough to fly, and it left the nest that evening. This was the second last chick to fledge in the Canberra study area this year, that I know of. It is the adult male who guards the chicks during the day.

The nest was set right above a popular walking and vehicle track on the edge of suburban Canberra.

This was the last chick I know of to fledge in the area this year, last week, mid-December. This family also nested on the edge of suburbia, and frogmouths are not the only woodland wildlife to be found close to houses. This Bearded Dragon was basking on the trunk of a small tree, trying to warm up on a cloudy morning. The frogmouths are on a branch in the top left.

Their grey plumage is in the same soft tone as the grey dead branch they are perched on. Tricky to see in grey light.

One final shot of a frogmouth chick in 2021. Once they fledge they are still dependent on their parents for food as they are still only half-grown. The family will disperse through the woodland and the fledglings will leave their parents territory by the end of summer. 

 Wet and windy weather

As of today, 15th, there has been 104 mm of rain in the Canberra area in November. 48 mm fell in the previous four days with 30 mm on the wettest day, the 11th. And it has been very windy, with gusts of over 40 km/h each day, peaking at 65 km/h on the 14th. So these have been testing times for birds with chicks, like this Tawny Frogmouth who was covering two chicks during the rain. 

This other frogmouth had his chicks tight beneath him. One is right beneath his belly, its tail and wing tips are protruding towards the camera, and its sibling is tucked under his breast feathers, face to the camera. The chicks are at a difficult age to protect from the rain. Their flight feathers are well formed, but their bodies are still mostly downy. If the down becomes wet they can become chilled and die.

This chick's body was lying below another nest, where the adult was still brooding two chicks. It must have been too difficult to cover three large chicks adequately. This chick died when about 18 days old. They fledge at about 28 days.

And at another nest, this chick died while trying to hatch. Perhaps the adults were intent on covering its siblings and so sat tight through the rain and wind, possibly too tight, and the chick could not push the shell open. It had opened the shell, as can be seen by the crack line around the top, but never left the egg. So close. The chicks bill can be seen above the slug - whose presence is an indicator of how wet the weather was.

I found this Brown Goshawk chick lying freshly dead below a nest in the same wood as the last frogmouth nest. It was not yet stiff with rigor mortis, nor found by ants, and it had been very windy earlier in the morning. The chick had a partially filled crop, as can be seen by the bulge in its throat, so the adults had been providing enough food. Wind blow was the most likely cause of death. There was still at least one other chick in the nest and the adult female was in attendance, looking after it.

The goshawk nest was set at the end of a slim high branch and it was bouncing about in the still brisk wind. The female was quick to return and protect any chicks in the nest as soon as I left the area.

I found two hatched goshawk eggshells below a tree where the adults frequently perch. There were lots of droppings below, that indicated this. And the adult female would have taken the eggshells from the nest and dropped them there. In the above shot, the cup-shaped membrane of the bottom half of a shell indicates where the chick had cut its way around the egg, then lifted the lid and popped out.

This lid of a goshawk eggshell shows the chip marks where the chick had pecked with its egg-tooth to prise open the shell. The pattern is similar to that around the frogmouth eggshell.

Young birds are so vulnerable to the weather.

Frogmouth - The most Instagrammable bird 

Here they are, images of what has recently been recognised as the most Instagrammable bird - the Frogmouths. I have been studying them, especially these Tawny Frogmouths, for over fifteen years, I have never used Instagram, but I agree that they have a special aesthetic appeal.

I first saw the news of their status on the BBC News at: https://www.bbc.co.uk/news/science-environment-56946165  This was an article on a study by K. Thommes and G. Hayn-Leichsenring in the journal i-Perception. They assessed the most Likable bird images using the number of Likes each type of bird scored on Instagram and ranked them by Image Aesthetic Appeal. See the full articles by clicking the clinks. https://doi.org/10.1177%2F20416695211003585

This is an adult female who although wild, would sit on her perch quite happily as I walked about within a few metres of her. They are nocturnal birds, so they rest during the day, sitting quietly on the same perch all day. Not all birds sit so calmly and allow easy photography, but this certainly helps their appeal.

Then of course, there are the super cute fluffy youngsters. They always watch with big wide eyes, front-facing, which is rare in birds and adds an anthropocentric touch. And they have that seemingly down-turned mouth. People will press like to such an image.

Once established as a pair, the adults will often sit on a perch snuggled up close side by side. They fluff up their feathers to keep warm and bask in the sunshine. More anthropocentric association. Of course people press Like to such shots.

There is a catch of course. Most frogmouths do not sit openly posed for photographers, and most photographers are unlikely to see one. For most frogmouths adopt a branch-like pose when they see people approach. They stretch their necks up, draw their feathers in, and stay motionless with eyes closed. Well, they peep through their eyelids, to watch for danger. And isn't their camouflage wonderfully adapted for concealment. How many Likes would this image achieve?

Or who could not admire how such a pair of beautiful birds can bask in the sun in full view of people walking below, yet never be noticed. That is what I appreciate most about them.

For more information on these wonderful birds browse through the other pages that describe their behaviour here on this blog. See the links on the right.

With special thanks to Thommes and Hayn-Leichsenring for bringing one of my favourite birds into the limelight.

Thömmes, K., & Hayn-Leichsenring, G. (2021). What Instagram Can Teach Us About Bird Photography: The Most Photogenic Bird and Color Preferences. i-Perception, 12(2), 20416695211003585.

Tawny Frogmouths are busy

Many of the tawny frogmouth chicks I have been studying this year have fledged in the past two weeks, like these two above, flanked by their parents. The family were sitting in a tree about 30 m from their nest tree. All were sitting quietly in the partial shade. Mum adopted a defensive hiding pose, adopting a posture to resemble a broken branch. Dad sat quietly, he had seen me often before and probably recognised me as no threat. The chicks were curious.

The chicks, like so many frogmouth fledglings, were so curious of the observer that they never adopted a defensive pose. They stared down at me as if determining what I was, and whether I was a threat to them. They were probably trusting in their parents for guidance. But they simply sat quiet and didn't give any soft alarm calls. Did the chicks feel safe because their dad wasn't alrmed?

Dad maybe looked calm, but I am sure he was ready to react were I to make any wrong move towards them.

There are numerous frogmouth pairs that did not seem to breed earlier, in september, as usual. But I have seen several new nests and birds on eggs in the past week, at the same time as most are fledging. This might be because there was limited food over winter and not all birds were in condition to breed in spring. Now though, with most pairs rearing two chicks, and some pairs rearing three, and it has been a wet spring, it looks like there is abundant food. I found this frog below one nest, and if this is an example of the prey available, that is a substantial meal for a frogmouth chick.

And I found this centipede below another nest. The kinks in the animal's body indicate where a frogmouth had grabbed it. I wonder what they taste like?

Autumn Frogmouths

It's now late autumn in Canberra and the Tawny Frogmouths are settling into their winter roosts. Each pair seems to have a favourite perch where they will spend most of the winter days, although they will occassionally move to other perches nearby. They like to use dead branches on the northern side of a live tree where they can bask in the sunshine. And they settle close to the trunk, where they blend in well with the background tree structure.

The female is usually perched behind the male, closest to the trunk. He is larger than her, and females in most animal populations are the more important sex as they lay the eggs. This female is peeking over her partner's shoulder. He might appear to be asleep in the sunshine, but he will be watching me through almost closed eyelids.

Even from a more favourable aspect to see them against the sky, they are still well concealed. They match the form of the dead branch as well as the colours.

This is how they were when I found them, basking with heads tilted back, to catch maximum warmth from the sun. And that was how I left them.