The Fishing Bat (Myotis macropus) is a splendid little creature that makes a living by dragging over-sized feet across the surface of pools and lakes to collect insects, small fish and crustaceans. It will also forage for aerial prey but is strongly associated with large bodies of still water. If you read the books, those bodies of water are fresh, elongate, and preferably of good water quality. The discovery by Leroy Gonsalves and Brad Law that Fishing Bats were active users of the estuarine waters of the Port Jackson (near Sydney) was publication-worthy and engendered quite a lot of huffing and puffing among the bat fancying classes.
The Fishing Bat is a pretty much ubiquitous feature of bat communities around water bodies in our part of north Queensland. If you are lucky, you’ll see them darting in and out of culverts (especially at St Margaret’s Creek) or flitting around the pontoons on the Aplin’s weir reach of the Ross River. More often, to be sure of what you are seeing requires a bat detector, a device which records ultrasonic bat calls and renders them visible as sonograms, or audible by reducing call frequency sufficiently to register in the human ear. Calls made by the fishing bat are pretty distinctive, and it is these calls upon which this tale rests.
Apart from the Ross River and St Margaret’s Creek, I have recorded Fishing Bat calls from Rollingstone Creek, Ironbark Creek, Emmett Creek and Spring Creek, as well as from a couple of lagoons on Rita Island in the Burdekin. It seems that if there is open freshwater, Fishing Bats will be there.
The Fishing Bat has not shown up in recordings from the mangroves reaches of estuaries on the Haughton River, Barratta Creek or Burdekin River, so it was a surprise to record good calls from Fishing Bats foraging over the flooded salt flats on the Cape Cleveland Road, close to its junction with the Bruce Highway. This locality is a well known fishing spot and bird watching venue, but in the past, it has been a bit of a batty wasteland. Not so this time.
From around 7 pm on the 15th of February, microbats were very active, feeding on masses of flying insects that swarmed shamelessly wherever a sliver of light was in evidence. The Fishing Bats were not alone. Additional species identified during the evening were Eastern Horseshoe Bat (Rhinolophus megaphyllus), Eastern Cave bat (Vespadelus troughtoni) Little Bent-Winged Bat (Miniopterus australis) and a Sheath-Tailed bat (probably the Yellow-Bellied Sheath-Tailed Bat, Saccolaimus flaviventris, but in that area it might also be the rare Bare-Rumped Sheath-Tailed Bat, S. saccolaimus). The Northern Free-Tailed Bat (Ozimops lumsdenae) and the Greater Northern Free-Tailed Bat (Chaerephon jobensis) were probably present. A number of other calls could not be identified.
A second evening of bat detecting (26th of February) added the Hoary Wattled-Bat (Chalinolobus nigrogriseus), Gould’s Wattled-Bat (Chalinolobus gouldi) and a species (unidentified) of Long-Eared Bat (Nyctophilus sp.) to the list but levels of bat activity, as represented by their calls, was much reduced in comparison to other nights. Also much reduced was the number of insects – it was possible to sit and read without being swamped by potential bat food. No calls attributable to Fishing Bats were recorded on the evening of the 26th.
A third evening of recording, on the 14th of April, also lacked calls from Fishing bats but did detect Yellow-Bellied Sheath-Tailed Bats, Eastern Cave Bats, Hoary Wattled-Bats and numerous Northern Free-Tailed Bats. Insect activity was so subdued that car windows could be left open with impunity.
Table 1 – Summary of species recorded by date
Mud flats along the Cape Cleveland road link the Wongaloo wetlands, which are predominantly fresh water, with mangrove creeks feeding into Cleveland Bay. Somewhat decrepit bund walls impeded free flow of water through the system. In the dry season, the flats and entrapped brine are hyper saline. In the wettest times during the wet season, the system veers towards freshwater dominated. At time of writing, neap tides and recent heavy rain have presumably pushed salinity levels down, but my taste–based digital salinometer (also known as a finger tipped in the water and then licked) suggests the water remains salty enough to sustain a claim that tropical Fishing Bats will use saline waters, as do their colleagues on Port Jackson. The extent to which bat behaviour and use of the salty water are comparable between these wildly disparate places remains to be seen.
The open foraging habitat at the recording site favours bats with high wing aspect ratios – they are fast but not so manoeuvrable. The Yellow-Bellied Sheath-Tailed Bat, Northern Free-Tailed Bat and Greater Northern Free-Tailed-Bat are of this type, and are commonly recorded near mangrove creeks throughout the Burdekin. The Eastern Cave Bat tends to forage over relatively small areas but is willing to fly over at least 500 m of grassland to reach a feeding place (Churchill 2008). Like the Hoary Wattled Bat, the Eastern Cave bat likes to forage over water. The Eastern Horseshoe Bat, the Little Bent-Winged Bat and the Long Eared Bats are clutter specialists, generally flying slowly within canopy or trunk spaces. They were recorded once each and were an unexpected presence. I can only presume that the abundance of insects was enough to lure them out from their usual haunts in forests on the rocky slopes of the nearby Mount Storth.
As a final observation, it is interesting to note just how many species of bats – at least 10 – were detected in the recording sessions. This is quite a respectable representation of the most frequently encountered bat species in the Townsville region and stands in stark contrast to the paucity of bats detected at the same site in the dry season. What a difference water makes!
Campbell, S. (2009) As long as it’s near water: variable roosting behaviour of the large-footed myotis (Myotis macropus). Australian Zoologist 57(2) 89-98
Churchill, S. (2008) Australian Bats. Jacana Books, Crow’s Nest, Sydney.
Gonsalves L. and Law, B. (2017). Distribution and key foraging habitat of the Large-footed Myotis (Myotis macropus) in the highly modified Port Jackson estuary, Sydney, Australia: an overlooked, but vulnerable bat. Australian Zoologist 38 (4): 629–642
š – ›