Category: warm, cold

Male desert locust protects female from sun

A female desert locust spends more than two hours to lay a batch of eggs in the hot sand of the Sahara. Usually, a male is sitting on her back, acting as a sunshade, Koutaro Ould Maeno and colleagues write.

Desert locust females produce about a hundred eggs at a time. They drill their abdomens into the sand and then sit still for more than two hours on average while the eggs leave her body. If they do the job during daytime, they must endure the scorching heat. How does the insect cope with that, Koutaro Ould Maeno and colleagues wondered.

They studied the behaviour of desert locusts, Schistocerca gregaria, in Mauritania during the so-called gregarious phase, when the animals live in groups. Males gather at leks during the day to attract females and copulate.

Possessive behaviour

After mating, a female stores the sperm; one mating provides enough sperm for several egg-laying sessions. A male invests a lot in mating, as it takes him hours. To ensure that she actually uses his sperm, he usually continues to guard her until she has laid eggs, keeping rivals away. This possessive behaviour limits her freedom to choose another partner, but in return she is not harassed by other males.

And it turns out to have still another advantage.

Most females lay their eggs at night, but some wait until the next morning. They avoid predators that are active during the cool night. But another danger is looming: it gets dangerously hot. Desert locusts can withstand much heat, but a temperature of 55°C or more is fatal, and it can get that hot in the sun. This is where the guard helps. When a female lays eggs, he sits on her back and functions nicely as a parasol, the researchers write.

Probably, this is also the case in a mating couple.

Cooler

Females that oviposit during the day cool down a bit because their abdomen extends into the ground; it is less hot there than at the surface. In addition, the researchers now show that an egg-laying female with a male on her back is cooler than a female without a guard. She is also cooler than the sand.

The guard himself also gets less hot than the sand because he is at a greater distance from the ground. When males attract females at a lek, they stand as high on their legs as possible to avoid overheating. In addition, the animals position themselves in such a way that they catch a minimum of solar radiation.

Desert locusts can live gregariously; then they gather, multiply rapidly and can become a plague that eats almost everything that is green, moving fast and far. But in dry periods they are solitary and occur in small numbers; the animals then live longer.

Willy van Strien

Photos:
Large: mating couple of desert locust. Adam Matan (Wikimedia Commons, Creative Commons CC BY-SA 3.0)
Small: ovipositing desert locust female without guarding male. Christiaan Kooyman (Wikimedia Commons, Creative Commons, public domain)

Sources:
Maeno, K.O., S. Ould Ely, S.A. Ould Mohamed, M.E.H. Jaavar, A.S. Benahi & M.A. Ould Babah Ebbe, 2024. Mate-guarding male desert locusts act as parasol for ovipositing females in an extremely hot desert environment. Ecology e4416, online 15 September. Doi: 10.1002/ecy.4416
Maeno, K.O., S. Ould Ely, S.A. Ould Mohamed, M.E.H. Jaavar & M.A. Ould Babah Ebbe, 2023. Thermoregulatory behavior of lekking male desert locusts, Schistocerca gregaria, in the Sahara Desert. Journal of Thermal Biology 112: 103466. Doi: 10.1016/j.jtherbio.2023.103466

Tufted puffin may be overheated after flying

Flying is strenuous for a tufted puffin and it causes high heat production. After landing, the bird has to cool down. The bill is used to dissipate excess heat, Hannes Schraft and colleagues report.

Puffins get their food from sea. They have relatively short wings that enable them to dive and swim under water, looking for fish and other prey. But the wings are less suitable for flying. To stay airborne and move forward, the wings have to flap in high frequency; the breast muscles work hard and much heat is produced.

Outside the breeding season, puffins usually stay at sea. But when they have a young to raise, they have to travel regularly between nest and sea. When a puffin approaches the nest with a mouth full of fish to feed its young, it is often overheated.

The birds have a strikingly large bill, which helps to get rid of excess heat during and after the flight, as Hannes Schraft and colleagues show. The object of their research was the tufted puffin, which breeds along the northern Pacific Ocean, for instance on the coasts of Alaska and Kamchatka and on the Kuril Islands.

Network of blood vessels

With a special camera, the researchers made infrared images of birds that rested after landing; they did so from a distance of five to ten meters, in order not to disturb the animals. They took images of bill and back every two minutes. From these images, they were able to calculate temperature and heat exchange.

The temperature of the back remained constant, but the bill gradually cooled down; after half an hour its temperature had decreased by about 5°C. Also the heat exchange gradually decreased after landing, and the portion dissipated via the bill became smaller; a puffin also loses heat through legs and feet. Apparently, the bill is most important for cooling shortly after flight.

The bill dissipates heat thanks to an extensive network of blood vessels; warm blood cools down a bit when circulating through these vessels, just as in a cassowary’s helmet.

The tufted puffin bears the white-yellow tufts to which it owes its name only during the breeding season, when both males and females are decorated. A pair produces one young per year, and the tasks are divided: both mom and dad will breed and feed their young.

Willy van Strien

Photos:
Large: Kuhnmi (Wikimedia Commons, Creative Commons CC BY 2.0)
Small: Matthew Zalewski (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

See how the cassowary manages to stay cool

Source:
Schraft, H.A., S. Whelan & K.H. Elliott, 2019. Huffin’ and puffin: seabirds use large bills to dissipate heat from energetically demanding flight. Journal of Experimental Biology 222: jeb212563. Doi:10.1242/jeb.212563

Southern cassowary dissipates excess heat via its helmet

How can the tropical southern cassowary stay cool at high temperatures? Danielle Eastick and colleagues show that it uses its helmet to prevent overheating.

Just because of its size and strong legs – with a dangerous dagger-like claw that can be 10 centimetres long – the southern cassowary is an impressive bird. It also wears a prominent helmet or casque. What could be its function?

Until now, that was a mystery. Perhaps the helmet amplifies the deep sounds that the bird can produce, some people thought. Or perhaps it is a decoration to seek the attention of possible partners, next to the blue head and the blue and red wattled neck, according to another assumption. Otherwise, it may protect the head when the bird is moving through dense vegetation at high speed, or involved in a fight.

But now, Danielle Eastick and colleagues come up with a different answer.

Easily overheated

The southern cassowary lives in tropical forests of New Guinea and Australia. Being a large and dark animal, it can easily become overheated at high temperatures, so it must have the possibility to offload heat. Eastick hypothesized that the helmet might offer that possibility and set out to test this idea. It turned out that she was right.

The helmet consists of fragile, spongy bone and is partly hollow; it is covered with a horn layer and has an extensive superficial network of blood vessels. Infrared images taken by a special camera revealed that the blood vessels dilate at high temperatures, and the helmet gets warm. Heat can be offloaded to the air. But when it is cold, the blood vessel walls constrict and only a small amount of blood flows into the helmet. It cools down while the heat of the animal is preserved.

The legs and the tip of the beak contribute to temperature regulation in the same way, but the helmet plays the most important role. When it is very hot, a cassowary sometimes plunges its head into the water to lose more heat.

Design

The possibility of thermoregulation had already been suggested earlier, but it was never studied extensively. There are some other tropical birds with a helmet that may help to offload heat; for instance, some hornbills have a helmet on the beak. And perhaps the helmet of some dinosaur species facilitated heat loss as well.

The fact that the helmet of the cassowary has a function for thermoregulation does not exclude that it also plays a role in partner choice. Although, to be honest, its design is not very impressive.

Willy van Strien

Photo: Paul IJsendoorn (Wikimedia Commons, Creative Commons CC BY 2.0)

Sources:
Eastick, D.L., G.J. Tattersall, S.J. Watson, J.A. Lesku & K.A. Robert, 2019. Cassowary casques act as thermal windows. Scientific Reports 9: 1966. Doi: 10.1038/s41598-019-38780-8
Naish, D. & R. Perron, 2014. Structure and function of the cassowary’s casque and its implications for cassowary history, biology and evolution. Historical Biology 28: 507-518. Doi: 10.1080/08912963.2014.985669
Phillips, P.K. & A.F. Sanborn, 1994. An infrared, thermographic study of surface temperature in three ratites: ostrich, emu and double-wattled cassowary.  Journal of Thermal Biology 19: 423-430. Doi: 10.1016/0306-4565(94)90042-6

Blowfly blows bubbles to prevent overheating

A blowfly often extrudes a liquid bubble between its mouth parts and then takes it back. By exhibiting this bubbling behaviour, it gets rid of excess heat, Guilherme Gomes and colleagues show.

How can a buzzing blowfly avoid getting overheated? Few people will ever have wondered, but as it happens, Guilherme Gomes and colleagues did. And they discovered that the oriental latrine blowfly Chrysomya megacephala manages to lower its body temperature by blowing a bubble.

At high air temperatures, a blowfly can expel a drop of liquid out of its oral cavity and hold it with its mouthparts. As some liquid evaporates, the droplet will rapidly cool down, whereupon the fly will take it in. The cycle is often repeated, and a droplet may tidally move out and back up to six times until eventually the fly swallows it and its body temperature decreases. The liquid is a complex mix of fluids derived from ingested meals and saliva.

Daytime and night-time

The blowfly applies this trick during the day when ambient temperature exceeds 25 °C. At that temperature, the animal is warmed-up and busy, so that its muscles produce a lot of heat, which makes cooling necessary. When it gets really hot, above 30 °C, the fly becomes inactive and no longer generates heat. It then stops blowing bubbles.

At night, it bubbles more than during the day to stay cool, in order to decrease its metabolism and save energy.

If air humidity is high, the liquid will not evaporate well and a bubble will not cool down. If the fly still expels a drop, it will not re-ingest it, but spit it out instead.

Small animals only

Cooling down by extruding a droplet is only feasible in small animals, and a number of insect species seem to exhibit such behaviour. For larger animals, it is impossible to produce and handle a liquid drop that is large enough for a cooling effect. To us, it would make no sense to trying it – fortunately. We cool down by sweating, which is impossible to an insect because of its chitinous exoskeleton and wax covering.

Willy van Strien

Photo: Blowfly Chrysomya megacephala. gbohne (via Flickr, Creative Commons CC BY-SA 2.0)

Source:
Gomes, G., R. Köberle, C.J. von Zuben & D. V. Andrade, 2018. Droplet bubbling evaporatively cools a blowfly. Scientific Reports 8: 5464. Doi: 10.1038 / s41598-018-23670-2