Sunday, 3 July 2022

Bats in the Fynbos

Lesser horseshoe bat
From a human perspective, the ability of bats to navigate in pitch darkness through the use of biosonar is undoubtedly remarkable. Not only do they have to be able to avoid obstacles, but also, in the case of the insect-eating species, to locate and identify tiny prey items against the background. Their ability to do this is affected by a number of environmental factors, and the exact nature of the echolocation calls, and how the bat interprets them, may affect which of those factors have the most influence.

For example, the distance that a biosonar ping can travel is affected by both the temperature and humidity of the air through which it travels. Since there are bats in almost every habitat suitable for insects to live, we might expect the way that they use their sonar to vary depending on the local climate.

Sunday, 26 June 2022

I Would Swim Five Thousand Miles...

Breeding can be an energetically costly business, whether that's the effort put into finding and attracting a mate, or that required to raise young. The latter is a particularly important factor in mammals, which can't simply lay eggs somewhere where there's plenty of food and hope that the hatchlings do well for themselves as, say, an insect might be able to. Therefore, we might well expect that mammals will feed more during the breeding season, to compensate for all that extra energy they will be using. 

For males, there can be a downside, in that all the time you are spending finding and eating food is time not spend wooing and mating with females. Thus, in animals such as deer, we may find that males actually eat less during the mating season than they do at other times because their mind is far too much on other things. But females, given the needs of both pregnancy and lactation, ought to be different.

Sunday, 19 June 2022

Leaf-Eating Monkeys: Treetops and Limestone Cliffs

Dusky langur
Although the term "langur" is perhaps most associated with the monkeys of India, the term has been used more widely to refer to a range of similar monkeys found to the east. In this sense, the term is really one of convenience, reflecting both the resemblance and the relatively close evolutionary relationship between the various monkeys in the group. However, the word "langur" itself comes from Hindi and Urdu which are, of course, not native languages of the lands to the east, so there has been a move in recent times to use more local names for some of the species. I'm going to stick with the names that seem to be most common in English language sources, but there is considerable variation and not always much consistency.

One of the better studied of these species is the dusky langur (Trachypithecus obscurus). These live in the Malay Peninsula, from the southernmost parts of Myanmar in the north, through southern Thailand, and across essentially the whole of Peninsular Malaysia. Over the last few years, a small number have also been spotted in residential areas of Singapore, presumably having swum across the Johor Strait from the mainland, but they are not native there. Although definitive genetic evidence is lacking, seven different subspecies are currently recognised, three of which occupy different regions along the peninsula, with the other four found only on certain small islands off the coast. 

Sunday, 12 June 2022

Miocene (Pt 31): Killer Armadillos and Far-travelling Raccoons

As the Miocene epoch drew towards its conclusion, the island continent of South America drew steadily closer to its northern counterpart. The gap would not be fully bridged by land until a few million years later at the end of the following, Pliocene, epoch but, when it did, many of the peculiar mammals of the southern continent would die out, albeit in many cases it was the subsequent Ice Ages and/or the arrival of humans that truly finished them off. One group that survived the experience, and that is still around today, is that of the armadillos.

Even so, armadillos were more diverse in the Late Miocene than they are today. Probably the most distinctive were the glyptodonts, which had solid, often domed, shells without the flexible bands seen in living armadillos. As the sweltering heat of the Middle Miocene faded towards temperatures closer to those we see today, grasslands began to extend across much of the southern part of the continent, and the glyptodonts adapted to it, switching towards an even more heavily grass-based diet than before. The resulting group of what we might loosely call "advanced glyptodonts" was the one that would later briefly cross over into the north and includes the most famous examples. In addition to certain features of their shell, they were distinguished by having teeth especially suited for chewing, with the high crowns suitable for grinding up grass and other tough vegetation.

Sunday, 5 June 2022

Ticked Off

Predators are not the only creatures to feed off other animals. Certainly, if you're an antelope, the obvious things to fear are lions, crocodiles, or whatever else might seek to ambush and eat you. But virtually all animals, and certainly all mammals, also suffer from parasites, a rather more insidious threat.

Very broadly speaking, parasites employ one of two tactics. Endoparasites live in inside an animal, often in the gut if they're any larger than single-celled organisms, although they can infect other organs. These are typically parasitic "worms" of one kind or another, and fighting them off is more a matter of an animal's immune system than of any behavioural traits (at least, once it's already infected). Ectoparasites, on the other hand, live on the outside of an animal, clinging to the skin and perhaps hiding among the fur. Fleas are an obvious example of this sort of parasite and grooming can be at least a partial defence against them.

Saturday, 28 May 2022

When White-footed Mice Invaded Michigan

When I'm describing a particular species of mammal on this blog, one of the first things I usually mention is where in the world it lives wild. Clearly, there are differences in the fauna of different continents or specific islands. Cougars, black bears, pronghorn antelope, and coyotes are all common enough in the US, but don't live in Europe. We have Eurasian and Iberian lynx, but not bobcats and Canada lynx. There are bison in Europe, but they're a different species than the American sort, and we only have wild raccoons because some were deliberately released in Germany in 1934. 

Clearly, the existence of the Atlantic Ocean is not to be sniffed at. However, this applies on a smaller scale, too, where some physical barrier that's some way short of an ocean, but is still significant, prevents an animal from advancing further across its home continent than it might like. 

And then there's the fact that animals have particular requirements as to the climate and vegetation of their native areas - even if the vegetation is only affecting the prey animals that they themselves need to feed on. The difference between this and the physical geography of rivers, mountains, and so on, is that it's changing over a much faster timescale, especially in recent decades. Animals may be forced to move to new areas, which can be a problem if the physical geography prevents them from doing so and can be a problem for other reasons even if it doesn't.

Sunday, 22 May 2022

Leaf-Eating Monkeys: Sacred Langurs of India

Sacred langur

In Hinduism, the monkey god Hanuman is a companion of Rama, one of the more popular incarnations of Vishnu, and represents, among other things, loyalty and virtue. The specific type of monkey most associated with him is known by various names, including "Hanuman langur" and the rather uninspired "northern plains grey langur", but I'll stick with sacred langur (Semnopithecus entellus).

As currently defined, the sacred langur is found across almost the whole of northern India where suitable habitat exists. The biggest limitation to that habitat is elevation; sacred langurs are very much a lowland species, not found above about 400 metres (1,300 feet) - which cuts out rather a lot of the more northerly parts of the country as it reaches towards the Himalayas. Other than that, they require forest, but they seem adaptable to different types. 

In practice, they mostly live in dry tropical deciduous woodland because that's largely what there is in that part of the world, but they extend into thorny scrubland in the northwest near the deserts of Rajasthan and into damper forests in the east. They are also common, probably due in part to their reputation as a sacred animal, on the outskirts of densely settled urban areas. A population is also found in southwestern Bangladesh, but they aren't thought to be native there and were likely brought across by Hindu pilgrims in the late 19th century.