Mosquitofish also eat tadpoles i e if you have Mosquitofish you won’t have any tadpoles maturing to froglets.
From: Con Boekel [m("boekel.com.au","con");">]
Sent: Friday, 15 August 2014 6:39 PM
To: COG list
Subject: [canberrabirds] Our Azure Kingfisher's prey identified - and a very discursive ramble through some byways of anecdotal knowledge relating thereto
One of the things that I used to think was that maybe Azure Kingfishers could not survive in the ACT in winter because there are no small fish near the surface in winter. (OTOH, maybe the AKs are just sensible...) But I don't know how deep AKs can dive...
Anyway, the shallow water species I see most often in the ACT is the introduced Mosquitofish Gambusia sp. Redfin predate them voraciously (I have seen Mosquito fish jump out of the water onto the shore in their desperate attempts to get away from Redfin). So Mosquitofish are not found in open water but near water vegetation, in the shallows and/or near the banks.
When the water is warm Mosquitofish are to be found in large schools very close to the surface. When the water is cold, they tend to stay near the lake/stream bed. Typically, I do not see them at all in Winter.
I should say that I did see the Azure Kingfisher yesterday, and the day before, thanks be to Steven and Lyndon who good naturedly ignored the fact that when they first spotted me I was lurking in the vicinity of some Angus cows.
One of the snaps I took shows the Azure Kingfisher with a fish that it had caught. While the details of the fish are a bit patchy, one detail does stand out, as it were: it has an gonopodium. As far as I am aware, the only species of fish with a gonopodium in the ACT is the Mosquito fish, Gambusia sp. The female is much larger than the male and has a bluish spot near the vent, perhaps to assist the male line up his gonopodium.
On the day on which I took the snap there had been ice riming the edges of Our ACT Kingfisher's Molongolo Backwater. So the water was cold. The water in which the Kingfisher was fishing looked to be less than about a metre deep.
Quite by coincidence, I saw Mosquito fish at or near the surface today for the first time this year, so the rime, and the ACT's run of morning minuses, did not keep that particular school from moving about. Perhaps they were motivated by some Redfin.
There is some speculation to be had here... how deep can AKs dive? Was this AK able to survive off Mosquito fish by diving to near the bed, rather than fishing from the surface? And, if AKs can survive off Mosquito fish by catching near the bed of shallows in winter, as well as from the surface in summer, and since there are many, many mosquito fish in the ACT, why aren't AKs here all year in copious numbers?
Mosquitofish must be the kissing cousins of Cane Toads. They were introduced to control mosquitoes, which they don't do very well, and they are themselves voracious predators on smaller native fish being, IMHO, a significant threatening process.
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