Skyrail Nature Diary: May 2015

This month we will be looking at bats, a group of animals often reviled and surprisingly little known to most people despite comprising 20% of all known mammals (1,240 species). Only rodents have more species. In the old days bats were called flittermice. Other Germanic languages still call them this. Bats are the only mammals that can truly fly as opposed to gliding from tree to tree.  Bats actually have several important ecological roles to play, all of them nocturnal. Many of them are very efficient insect eaters, about 70% of them overall. A significant number are important pollinators of plants that flower at night. Here in the Wet Tropics, the two best examples of plants with night flowers are the Fish Poison Tree and the Cocky Apple. Most plants that flower at night seem to be desert plants, the Sonoran Desert in Mexico being a prime example.

Some of the world’s largest bats eat fruits and disperse their seeds, mostly rainforest fruits. So what exactly are bats? Well, bats have unique wings comprising of their five strongly elongated fingers stretching a web of strong skin known as the patagium. This web extends to the hind legs and the short tail. As a result, bats are clumsy on the ground and prefer to rest hanging upside down by their specialised toes. In New Zealand there are two species of bat that prefer to move around on the ground, presumably because there are no serious predators that feed on them. The world’s smallest mammal is very possibly Kitti’s Hog-nosed Bat. This bat is only 29 to 34 mm across the wings and weighs no more than 2.6 g.  There are two groups of bats today, the mega-bats and the micro-bats. The main differences between the two groups are that micro-bats alone have echolocation and their ears don’t close to form a ring. Bats are most closely related to the ungulates (hoofed mammals) and the carnivores and not to rodents as previously believed.

Flying Foxes are mega-bats and the largest bats in the world. The Giant Golden-crowned Flying Fox has a wing span of up to 1.7 metres and can weigh up to 1.6 kg! They all have dog like faces and are probably the only bats that occasionally are considered to be cute. All Flying Foxes are frugivorous, which means that fruits are their mainstay, especially figs. Most Flying Foxes appear to be unable to digest solids and therefore chew the fruits to extract the juices and spit out the pulp. Either way Flying Foxes are very efficient at dispersing fruits, thereby helping to spread the plants in question. Flying Foxes don’t have echolocation and instead rely on an excellent sense of smell and good night vision. Colonies of social creatures can be absolutely massive and they tend to be noisy buggers as anyone living near their colonies can attest to. Sadly many species are now endangered due to human settlements and farms encroaching on their habitat.

Both mega-bats and micro-bats have representatives that are important pollinators. Here in the Wet Tropics, the Tube-nosed Bats and the Blossom Bats are the most obvious species to live off pollen and nectar rather than fruits. Tube-nosed Bats have the most unusual nostrils of the world’s mammals. The Blossom Bat is a tiny bat no larger than 60 mm long and is found in North East Queensland and Papua New Guinea. Both of these species are mega-bats and important pollinators in the Wet Tropics.

Insectivorous bats comprise 70% of all bats and are often considered important in controlling the world’s insect populations. Even some farmers recognize this fact and welcome them onto their properties. This is certainly cheaper and safer than insect poison. Insects are located by echolocation while on the wing. The bats achieve their sonar by specialised noses and ears. Many bats have bizarre looking noses designed to concentrate their sonar. Their ears are among the most advanced of any mammal with several skin folds oriented for maximum detection of returning echoes. Some moths have devised ways of jamming the bats’ sonar to confuse them while hunting. Many bats seem to like caves and enormous deposits of bat guano tend to accumulate on the cave floor. Some of this guano is harvested commercially as fertiliser. The danger of roosting in caves is the sometimes very low temperatures and predators waiting to pounce near the entrance at dusk. Some snakes are very good at catching bats this way.

A small number of bats are carnivorous and at least one species of bat is piscivorous (eats fish). Here in Australia, the Ghost Bat is one of our largest bats despite being a micro-bat and is a ferocious hunter. Any animal of the right size out at night is fair game for this efficient hunter. The Ghost Bat’s teeth are more substantial than those of the insect eaters. This bat’s name refers to the bat’s thin wings that look ghostly while flying. Ghost Bats roost in caves and mines. The Fish-eating Bat of California is probably the only species of bat to specialize in catching and eating fish. They have large feet with sharp claws that are perfectly designed to snatch fish and crustaceans out of the ocean eagle style. The tail’s web appears to be used to assist in catching the animal’s prey. Fish-eating Bats can drink sea water thanks to their amazing ability to concentrate their urine.

By Tore Lien Linde

*Image courtesy of Natalie Schneider