Sunday, 17 January 2021

Sperm Whale Bromance

While there are a few exceptions, there is a general rule among mammals that males travel far from home when they approach adulthood, while females tend to stay in their local neighbourhood. The purpose of this separation is to ensure that, once they become sexually active, the females that a male is going to have the opportunity to mate with aren't all his own sisters or close cousins. Many mammals live essentially solitary lives, so this is merely an issue of the male travelling further than the female when he leaves home; other than that, their social lives aren't really all that different.

In social species, however, the end result is that herds (or other groupings) are united primarily by their female relationships. The females in a herd are likely sisters or other close relatives, while the males have travelled from elsewhere and are not only not closely related to the females, but may not even be closely related to each other, either. Often males spend some time living on their own before they find a suitable herd to join (perhaps because the existing dominant male is getting on a bit) with the result that there's a distinct female-bias in membership of the group. 

Sunday, 10 January 2021

The Sexy Face-Masks of Lekking Bats

The mating behaviour of mammals is, unsurprisingly, highly varied across different groups and species. We would hardly expect the behaviour of dolphins to resemble that of reindeer, for example, or hedgehogs to resemble cheetahs. Reproductive information is one of the key biological factors we tend to look at when describing a species, even if it isn't quite as easy to evaluate as, say, diet or habitat. (Or anatomy, of course, which doesn't even necessarily require the animal to be alive). Look at almost any write-up of a mammal species in an encyclopedia, and there'll be something on reproduction - assuming we know it.

But, for a great many mammal species, we don't. This may be because it's rare, or difficult to observe in the wild, or perhaps that it's a newly discovered species that we can reasonably assume isn't that different from close relatives we already knew about. But, at least when it comes to reproductive behaviour, one of the biggest gaps in our knowledge concerns the bats.