Month: May 2023

[All these photos and videos were taken last week at Gardens in the Wild in Framingham, Massachussets, the home of the New England Wildflower Society. Highly recommended! and the frogs are used to people, so they are much less skittish than they are around me in Maine. ]

The American Bullfrog, Lithobates catesbeianus, is a substantial chap. He can weigh up to 0.5Kg, more than 1lb. The bullfrog male’s mating call is low in pitch, with a frequency around 200-300Hz, and can be heard for up to one kilometer. Here is a recording (made in Maine a year or two ago.)

These calls are very very loud, and yet they call with their mouths closed. How do they do it?

When the male calls, he fills his bright yellow throat pouches with air. Each call lasts approximately 0.5 seconds: I have slowed down this video so you see this more clearly:

I had always thought that was why his calls were so loud.

But it turns out that is wrong. The inflated pouches are used as a sort of air reservoir so that air can be recycled to the lungs across the vocal folds where the sound is actually produced. Some sound is indeed then transmitted to the world through these pouches, but that is not the main source. The male has a greatly enlarged tympanum (ear-drum), the round patch behind the eye, as you can see in the photo.

It is this which hugely amplifies the sound energy, being responsible for some 98% of the energy actually transmitted. (Purgue 1997). Its resonating frequencies match those of the calls, so effectively it acts as a drum. (Purgue says you can see the eardrum move, but even when I slow my videos right down I can’t detect this!).

Even if I can’t see the eardrums move, what I can see is the whole body vibrations that are transmitted to the water: look at those ripples radiating outward as the frog calls.

Note also how much smaller the female’s ear-drum is: hers is used just to transmit sound to her inner ear, like ours.

There is always something new to learn: who knew that ear-drums could be a two-way sound system. They even look just like a high-end stereo speaker!

PS More on the generation of the initial sounds: (Ryan and Guerra 2014) ” In most frogs, air is expelled by contracting trunk muscles surrounding the lungs, which pushes the air through the larynx .. The incoming air causes the vibration of the vocal cords and the larynx itself. The air then enters the buccal cavity and passes through the vocal slits to inflate the vocal sac. One of the most conspicuous and near-universal traits of male frogs is the vocal sac. Its main function is to recycle air from the lungs to the vocal sac and back again. The vocal sac also radiates sound.”

PPS The kettle-drums used in classical music are more formally called timpani, essentially the plural of the same word as an ear-drum, tympanum. Hence my title.

PPPS It took about 250 photos to get those two still shots of the 0.5 second period when the vocal sac is inflated!

Although The Gambia was a bird-focussed trip, rules are made to be broken.

Nature tends to be symmetrical: creatures have two hands, four feet, six legs, eight tentacles etc. West African Fiddler crabs, for example, have eight legs and two front pincers, and the females look the same on both sides, unsurprisingly.

BUT, the males are in no way even-handed: one claw is huge and one is tiny. Here is a typical male Afruca tangeri, abut 50mm (2″) wide and 25mm (1″) long, feeding in the tidal mudflats of the mangrove swamps:

The tiny claw is used to delicately select minute portions of food, and the huge claw is used to fight other males:

but also to attract the female, who goes for a nice big claw (and also for the most impressive claw-waving dance.)

Their Portuguese name is ‘boca-cava-terra‘, meaning “mouth-dig-earth”. The small claw is used for feeding, finding food in the mud, and then carrying it to the mouth:

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They filter through the muddy mouthful, and then drool out the unwanted residue; their mouth is just below where the two white markings converge:

I took a video of them feeding, all the while keeping their stalked eyes on the other guy. (Notice how the left-hand one occasionally uses his smaller pincer t0 knock off the accumulated debris from his chin.)

The male population is roughly 50:50 left-clawed vs. right-clawed, and depending on their relative claw placement they seem to have techniques for fighting face-to-face or side-by-side. This video shows a different species in combat:

The local Green Monkeys forage for these crabs. Here is a youngster, who came away from the mud-flats empty-handed:

PS Imagine if we used our left arm only for fighting, and our right hand only for eating. Sounds awkward? In fact there are indeed human cultures in which only the right hand is used for food, so we are not as distinct from the fiddler crab as you might imagine.

PPS Now that I think about it, crabs are ornery in other ways too. Most of the world’s creatures navigate the world forwards, but crabs famously scuttle along sideways. I wonder if their brains are just wired differently?

[This is my last kingfisher post from the Gambia. I’m going to give you a break from birds for a little while now, I think. That’s the plan, anyway!]

The Striped Kingfisher, Halcyon chelicuti, is a mere 17cm long. It is another woodland kingfisher.

It swoops down to the ground from around 3m high, to catch insects, with an 80% success rate.

The Malachite Kingfisher, Corythornis cristatus, is a proper kingfisher: it actually fishes, from perches around 2 feet above the water, and prefers shallow water only a few inches deep..

The tiniest of all, at 13cm, it is exquisitely plumaged, a tiny flash of iridescent blue in the mangrove roots:

[A little late for US Mother’s Day, which was two days ago, but worth suspending my kingfisher posts for.]

I slammed on my brakes, because out on the grass in front of a nearby house was a mother red fox with four cubs. No camera, and my beagle quivering with excitement in the truck. So I drove home (5 minutes away), dumped the dog and grabbed the camera.

She was very relaxed, but vigilant:

The cubs were skittish, and scattered when I stopped the truck. They only emerged one at a time:

There was a large rock partly screened by leaves, so they felt safer there, and she groomed them:

Then this one took a nap:

The cubs were quite large:

and copying the mother’s every move:

The cubs looked healthy, and so did she, until she ran.

It then became apparent that although she moved fluidly and fast, she only used three legs, and that her right front leg was injured. Here is a close-up of her front feet, showing that the claws on the unused foot have grown long from lack of contact with the ground:

The leg also looks thinner, as if the muscles have wasted. According to a neighbor, she has been injured for four years, and despite that she has raised cubs every year.

She gets my mother-of-the-year award, Fantastic Mrs. Fox (with thanks to Roald Dahl.)

The Giant Kingfisher, Megaceryle maxima, is a majestic bird measuring 46cm (18 in) . The female (below) has a streaked chest and a reddish lower belly; the male reverses the coloring!

I only ever saw females on this trip,

Although in Zambia five years ago I did see a male:

Back in the Gambia, this one diving on a fish could have been either:

They eat mainly fish, but also frogs and even crabs. And that beak must strike terror into the heart of any target: this is the view the victim gets just before the denouement.

Not as big at 25cm, but far more cheerful, is this Blue-breasted Kingfisher, Halcyon malimbica:

From behind it is a brilliant turquoise:

It is a tree kingfisher, and not a specialist fish-eater. It mainly eats invertebrates, including insects and crabs, beating them on the ground before eating them. That huge bill must help.

[We saw several different kingfishers in The Gambia, each in their own way lovely, so I’m doing three posts just about them. ]

Pied Kingfishers, Ceryle rudis, are common throughout sub-Saharan Africa.

I’m showing you this one because he repeatedly dived into the pool and returned to the same perch, so I took a burst of shots, and put together this sequence; the two black breastbands tell you it is a male:

He launched himself:

Dived,

and emerged..

and back to his perch. And all in a total of two seconds:

Later the female (only a single black breast-band) had a dip from a separate perch: