Aug 30, 20217 min read

Species Uncovered; The True Face of Bats

Updated: Aug 31, 2021

A Mindset Renewal

This week, I am inspired by the knowledge gained during in-field experiences in Tobago. Upon observing these rich ecosystems and engaging different species of fauna in the north-eastern region of the island, which is now declared a UNESCO Biosphere Reserve under the Man and Biosphere Reserve Programme (MAB) [1], I gained a renewed appreciation for these flying mammals, known as Bats!

Yes, I know; you are probably thinking how interested one could be in these so-called “creepy nocturnal animals”? But, the truth is…… Media and Hollywood have given Bats a terrible rap. They are often reduced to “blood-sucking disease-carrying” animals. Though they can transmit diseases, there is, in fact, only ONE family known as (Phyllostomidae) Leaf-nosed Bats under the sub-family (Desmodontidae), which are home to three Bat species commonly known as the Common Vampire Bat; (Desmodus rotundus), the White-winged Vampire Bat (Diaemus youngi), and the Hairy-legged vampire Bat (Diphylla ecaudata) which are sanguivorous, feeding on the blood of mammals during their inactive hours.

Additionally, the notion of “sucking” on its victim is also an over-exaggeration. Meaning, Bats do not suck, but they utilise heat sensors to locate the veins of their warm-blooded prey. According to National Geographic [2], the Bat has a heat sensor on its nose; once a vein is found, it then bites, followed by lapping the blood with its tongue as it oozes out. The Bat`s saliva prevents the blood from clotting, and another chemical numbs the prey`s skin so it does not wake up. Additionally, unlike other species of Bats, vampire Bats can walk or crawl which helps them to attach to their prey.

So now that we cleared up the mode of feeding for Sanguivorous Bats, we can now focus on the general morphology and various feeding guilds of these diverse flying mammals. We will then come to understand their vital ecosystem and economic functions.

Now let`s get into the Taxonomy ……

The scientific name for Bats is Chiroptera, the Order they belong to, and it is Greek for “hand wing”. This describes the Bat`s characteristic feature of having four long fingers and a thumb connected by a thin skin membrane, as shown in the images below.

Bats, as mentioned above, belong to the class Mammalia commonly known as (Mammals). Remarkably, they are the only mammals capable of actual flight for sustained periods, and they are even more manoeuvrable than our commonly sighted birds.

Feeding Guilds and Ecosystem Function

Bats are diverse, and there are many feeding guilds (which refers to their feeding behaviour). These guilds include Frugivorous, Insectivorous, Nectarivorous, Piscivorous, and, as mentioned above, Sanguivorous behaviours. I know these ecological terms can be hard to digest, so allow me to unpack them.

Frugivorous Bats are our fruit-eating bats, and they aid in seed dispersal, which is extremely important in allowing tropical rainforests to grow. Especially under current high rates of deforestation and climate change, this is a crucial ecosystem function. Affirmed in a review article on the Ecological and Economic impact of Bats on Ecosystems; Tropical Forest is notably dependent on fruit-eating birds and mammals, citing (3) three fundamental reasons. These include; 1) allowing seedlings to escape from natural enemies (i.e., vertebrate and invertebrate seedeaters, herbivores and fungal pathogens), 2) reduces the competition among seedlings if they were to germinate in high-density areas around the parent plant and, 3) wide geographic spread allows the plant to colonise new habitats [3]. For example, in Central Panama, the Jamaican Fruit Bat carries single fig fruits some 100-250 (m) away from the actual fruiting plant. In West Africa, Bats carry 90-98% of the seeds of “Pioneer Species” [4]. Evidently, they play a critical role in maintaining the genetic continuity of different species. Below are pictures of typical fruit-eating bats found in Tobago, which I observed during my Bat sampling activity at Hillhouse Charlotteville. Check out our fellow Jamaican Fruit Bat (Artibeus jamaicensis), the Hairy big-eyed Bat (Chiroderma villosum) and Seba’s short-tailed Bat (Carollia perspicillata).

Jamaican Fruit Bat

Hairy big-eyed Bat

Seba`s short-tailed Bat

Insectivorous Bats specialise in consuming copious amounts of insects, acting as a natural pest controller/suppression for plants and crops. They carry out this role in both human-altered and natural landscapes. Thus, this can often translate into farmers relying less on toxic pesticides, resulting in cost savings. To monetise this function, I refer to the US National Parks Service, where it is quoted that the insect-based diet of these Bats amounts to $3.7 billion worth of pest control each year in the US [5]. Astonishing! I would say, so imagine what the global worth of these flying mammals could be? To this end, the loss of Insectivorous Bats is multiplied at an alarming rate with increasing dependence on pesticides [6]. Some examples include; Thomas’s yellow Bat (rhogeessa io) and the Brazilian brown Bat (Eptesicus brasiliensis), also found in northeast Tobago. Check these guys out below.

Thomas`s Yellow Bat

Brazilian Brown Bat

Nectarivorous Bats, as the first half of the word, would suggest, these bats feed on nectar. Nectar-drinking Bats facilitate the pollination of plants to allow the growth of fruits. National Geographic [7] documented that more than 500 plant species depend on bats for pollination. Some common species are our mangoes, bananas and avocados. I am sure many West Indians could not imagine a life without these on our kitchen tables. These also contribute to the genetic continuity of varying species. An example includes the Geoffroy’s Tailless Bat (Anoura geoffroyi), observed at the Hillhouse study site during my field studies.

Geoffroy`s Tailless Bat

Piscivorous Bats - Now, I know many of you would never link Bats to fishes/crustaceans in the same word/sentence. However, mother nature never fails in her ingenuity. An example found in Trinidad includes the (Noctilio leporinus), commonly known as the Greater Bulldog Bat from the family (Noctilionidae). These are a bit unique due to the food source as they are our fish-eating specialists. Typically found around harbours, lakes, and rivers, they utilise their huge feet to trawl through the water, catching any small fish that may be present [8]. The Greater Bulldog Bats utilise a special feature called echolocation; once it detects a fish, it then strikes rapidly by snapping its hind feet downward and forward into the water. Other methods are characterised by the Bat`s dragging their feet through the water up to 10 meters in areas where the fish stocking density is high [9]. Check out their massive feet, which aid in their nightly fishing expeditions.

Greater Bulldog Bat

Sanguivorous Bats, as mentioned above, feed mainly on the blood of other vertebrates, which is also known as hematophagy. Vampire bats in the wild feed mainly on large livestock such as mammals usually resting at night (i.e., cattle, pigs, goats, horses and domestic poultry) [10]. Examples are visually shown below of three typical vampire Bats.

White-winged Vampire Bats

Common Vampire Bat

Hairy legged Vampire Bat

There are also occurrences of Bats having multiple feeding guilds. Some species may have a (primary) feeding guild and a (secondary) feeding guild. For example, some species can be both frugivorous and nectarivorous. According to the Online Guide to Animals of Trinidad and Tobago, the Greater bulldog Bats show behavioural flexibility with fish and insects being foraged throughout the year, with insects being most important during the wet season and fishes during the dry season [11]. All in all, Bats are night shift workers, carrying out critical functions to ecosystem balance and human activities such as agriculture. We ought to never discount them. Also, the excretory matter from Bats, commonly known as (Guano), is essential for increasing the productivity of agroforestry systems as it is cited as an excellent fertiliser [12]. It is noted that this (Guano) contains insect fragments, arthropods, mice, fish, nectar, hair, pollen, and other valuable nutrients[13].

So how does an Ecologist study these fast-flying mammals???

Wildlife ecologists usually employ a Mist Netting technique or a Triple High Mist Netting Pole System. These nets are extremely thin, making it difficult for the Bats to see. Once the mist net is expanded in the sample area, the Bats, when they become active, accidentally fly into the nets, becoming tangled (however, this does not hurt them). Take a look below.

Bats caught in Mist Netting System

A trained specialist then untangles the Bats, and all necessary data is collected. This data often includes; the sex (i.e., M/F), age (i.e., adult or juvenile), forearm length, reproductive stage (non-visible testes, visible testes, non-parous, parous – non-lactating, non-parous – pregnant and pregnant. The Bat`s weight is determined by subtracting the total Bat and bag weight from the bag`s weight. Importantly noted is the species of Bat, which is deduced via the use of diagnostic keys.

The triple high mist-netting pole system follows the saying of “bigger is better”. These nets go high above the ground (24 feet) and serve the same purpose of capturing these swift animals. They consist of poles and a hoist system[14], allowing the researchers to reach the Bat from the nets at varying heights. Let’s take a look….

Triple High Mist Net Pole System

Flying Foward.....

Despite all the misconceptions surrounding Bats, there are vital to humans and the environment. Though they may hide during the day and become active at night, these unique flying mammals are hard at work, putting in overtime for us. I hope after reading this, your fear and apprehension of Bats become minimal, and your appreciation for them are augmented due to their apparent Economic and Ecological importance.