As mammals, we know bats need water in order to survive, but when you think about it, can you imagine how bats get their water intake? Watching a bat drink from a river or pond is an amazing albeit brief sight, the kind where if you blink, you miss it. But bats also need freshwater ecosystems for a whole host of other reasons. This blog will explore the many associations that bats have with freshwater systems across the world and highlights the need to protect and conserve them.
Bats and Rivers
Rivers are important for humans and wildlife alike, providing freshwater, a means of travel and food resources. They host a wide variety of aquatic species, including those which can be used to investigate the health of river systems, due to their pollution tolerances. Rivers are not only a primary source of water for bats, but also provide bats with much of their insect prey.
Insectivorous bats feed on a variety of aerial insects, including many species which start their lives as larvae in the river sediment and emerge in their winged adult form. Examples of these species are mayflies and true flies, which little brown bats in Canada are known to mostly feed on. In Canada, other bat species including the endangered tricolored bat and northern myotis also strongly rely on river systems for foraging. Rivers can also serve as navigational landmarks for flying and migration, with the added benefit of plentiful foraging opportunities along the way.
As a result of the services riverine systems provide for bats, overall bat activity tends to be higher around riverine systems. This has been demonstrated in studies across the world, including Poland, South Africa, Italy, Namibia, USA, Australia and Canada.
Bats and Wetlands
Similar to rivers, wetland habitats provide vital foraging opportunities for bats. Wetlands are some of the most biodiverse ecosystems on the planet, with wetland complex size and connectivity of systems being important components of prey availability.
In the same way that rivers are important for bat navigation, wetland habitats provide vital migratory stopover locations in which to feed and roost. Presence of wetlands, natural or artificial, are important for bats within agricultural, urban and dry landscapes, where there is often limited opportunities to forage sufficiently.
A recent study conducted a review of 116 publications concerning bats and wetlands, to generate a knowledge index and identify research gaps. They found that across Canada, Russia and several European countries, there is a low value of bat knowledge, compared to countries including Brazil, USA and Australia. One of the major findings was a large gap in research for energetically demanding periods for bats (e.g. migration and overwintering), meaning there is a lot more research needed to fully understand the importance of wetlands for bats globally.
Bats and Still Waterbodies
In addition to rivers and wetlands, ponds and lakes are also important forging locations for bats. Ponds which are surrounded by woodland habitat are likely to have higher local bat richness, and in some regions such as acidic mountains, are more important to bats as a source of drinking water than as a source of prey. The importance of lakes for bats is generally understudied, however, permanent large waterbodies within the Amazon saw more foraging activity than neighbouring rainforests.
The often smooth surfaces of ponds and lakes mean it is easy for bats to find these waterbodies using echolocation and even juvenile bats show innate responses to echoacoustic recognition of water surfaces. Regarding echolocation, bats often find it difficult to hunt in cluttered environments (i.e. locations with lots of vegetation such as dense forests), because echoes reflecting from the vegetation mask the acoustic signature of prey. Pond and lake habitats offer bats with largely uncluttered environments in which to echolocate for prey, with species including little brown bats having adapted to feeding over lakes by having a longer maximum perceptual distance.
Human Pressures on Water Sources Used by Bats
Worldwide, rivers, lakes, ponds and wetland ecosystems are under increasing pressures from human activity. The degradation of freshwater systems is particularly concerning for bats, who depend on healthy ecosystems to survive. A combination of climate change and human pressures are resulting in increase drought and aridity, resulting in the loss of 33% of the world’s wetlands. Ultimately, this results in the loss of drinking water sources for bats.
Water scarcity is not the only pressure on bats, water pollution directly influences both the abundance of key prey species and the health of bats. Bioindicator macroinvertebrate (bug) species, such as mayflies, caddisflies and stoneflies are highly sensitive to poor water quality, meaning high levels of water pollution result in huge losses of these species from aquatic communities. Tolerant macroinvertebrates, such as species of true flies, persist in poor water quality and ingest microorganisms, which concentrates the pollutants in their bodies. The accumulation of environmental contaminants from bugs to bats has been shown to affect bat immune responses and even damage bat DNA.
Another form of pollution which negatively effects the ability for bats to forage over water is the influence of artificial lights. When frequently shone on freshwater habitats, artificial lights reduce insect abundance and subsequently bat activity for most species.
Summary
Overall, bat species across the world have strong relationships with freshwater, mainly relating to the foraging opportunities provided by rivers and standing waterbodies. There is the need for more research into understanding these relationships across different geographical scales and particularly in locations including Canada, where there is a lack of bat-freshwater research. It is important to consider bats in freshwater conservation management actions, to safeguard important drinking and foraging resources and prevent losses of bat populations.
For information on World Water Day 2021, visit the official website here.