Hyla versicolor


Photograph by Darren Garrison.


Hyla versicolor – gray tree frog. Mr. Garrison writes, “BTW, the frog can change its skin color somewhat – they used to hang around my elephant ear plants a lot when I was drip-irrigating them (setting up a mini-biome.) I’d often look out and see one of the frogs clinging to the outside of a window. But sometimes they are dark colored like the one in the first photo, and sometimes white (but always with the yellow patches on the rear legs).”


It’s not easy being green.

Since the topic of the photo is coloration in urban environments, with Matt’s indulgence I will report an suggested example of differential predation due to coloration.

I live in a neighborhood in the front range corridor of Colorado. We are pet-sitting this summer. The pets are a medium-sized friendly dog and a small decorative pond in the back yard containing goldfish and Japanese Koi. The homeowners report that two years ago they used to see great blue heron stalking and preying on the fish in their pond! The husband would often look out his office window and see heron standing by the side of the pond and watching the fish swim back and forth.

There were 5 white Koi fish about a foot long, and one dark-colored one. My neighbors never actually saw the heron stab and catch a fish, but after one of these fishing episodes, suddenly one of the Koi would be completely gone. Eventually all the white ones disappeared, leaving only the dark-colored one. The survivor is really big now - about two feet long. He/she is dark on top and orange on the bottom, and very hard to see down in the pond.

There are smaller goldfish and Koi also in the pond, about 4-8 inches long. I think my friends restocked, but evidently some pair of fish had babies, too. Now there are about 15 fish in the pond, including the big dark-colored one. About a third of the pond’s surface is covered with lily pads.

My neighbors have seen signs of predation by raccoons as well: They have spotted raccoons around the pond at night, and have found fish skeletons elsewhere in their yard. But the heron-poached fish seem to disappear without a trace.

Other information: The pond is 8 feet long, 5 feet wide, and 3 feet deep in the center. They have a little fountain pouring into it. It feezes about 10 inches thick in winter; my neighbors have an electric heater that maintains a small hole. The herons come in the spring. Their back-fence neighbor has a larger pond and a little stream, and the herons hang out on the roof of a tool shed over there. Several trees shade the goldfish pond.

The herons stopped coming to our neighbors’ back yard when they got the dog. I think of my back yard as a safe and peaceful place, but maybe I’m wrong.

Questions for the august company at Panda’s Thumb:

  1. Has anyone else observed similar examples of urban predation?
  2. Is this a valid example of differential predation and survival due to advantageous coloration?
  3. Do heron jab at their prey and pick them apart like hawks, or swallow the fish whole?
  4. Are Koi and goldfish the same species?

Carl Drews said: Has anyone else observed similar examples of urban predation?

Yes. Both herons and raccons are common predators of backyard fish ponds. See, amonf many others, http://www.watergarden.org/Pond-Inf[…]nd-Predators

Is this a valid example of differential predation and survival due to advantageous coloration?

Very likely.

Do heron jab at their prey and pick them apart like hawks, or swallow the fish whole?

They swallow them whole - they usually catch them in a sideways pincers grip, then sometimes throw them up in the air to get them going down their throat headfirst. See http://stock.tobinphoto.com/heron-e[…]ures-533.htm

Are Koi and goldfish the same species?

Well, they’re all carp, but different species. “Koi may also interbreed with the goldfish to produce a sterile hybrid fish.” - http://en.wikipedia.org/wiki/Goldfi[…]ated_species

If people are gonna put out bait for herons and raccoons, then of course they will sometimes take that bait! ;)

One way your neighbor can keep the raccoons busy and the koi safer is to add “rosy red” fathead minnows to the pond. They’re a pale orange or pink color color morph of a native Midwestern minnow. They also have the benefit of acting as dither fish for the larger species and help them feel secure enough to swim in the open when there are no predators around. So they serve as an early warning system for the big fish, and as a convenient distraction for predators. Fatheads are at least as tough as goldfish when it comes to their temperature preferences, and can do just fine under a crust of ice in the winter.

They’re really very interesting fish in their own right as the breeding habits are almost unique among minnows: the male occupies a cave, a hollow, or an overhang and cares for a clutch of eggs. While they’re incubating he guards them, fans them, and rubs a fungicidal secretion over them. Most cyprinid fishes (including all other minnows, barbs, and carp like your neighbor’s koi) don’t display any brood care at all. The fatheads breed like underwater rabbits (though not to the same extent as guppies), and the excess fry are good eats for the larger fish. You don’t need that many initially to establish a good-sized population in the pond. A dozen or so would do the trick if they can avoid being eaten long enough to spawn. A few small lengths of 4” diameter PVC pipe or small, overturned terracotta pot makes a good hiding place/breeding cave. Predation by wildlife and the other residents will help keep their population in check. Meanwhile the minnows will do valuable services as dither fish, mosquito control, decoys for predators, and add visual interest with their constant activity.

Fatheads have also become very popular model organisms in the lab. Toxicology literature is packed with studies done on these fish, and as a social animal they’re also important for behavioral studies. An injured fathead releases schreckstoff (literally “scary stuff”), a phenomenon first discovered in 1938 whose chemistry is only recently becoming understood. The substance warns other fish in the shoal that a predatory is probably on the hunt; uninjured fish react with fear and avoidance behaviors when they detect the stuff. It’s still not clear how this kind of chemical signaling system became fixed by evolution; the injured fish doesn’t exactly benefit from it. It could be kin selection, since the shoal is likely related to the injured fish. It could be that evolution simply favored fish that reacted to schreckstoff with alarm. Regardless of how it came about, if the koi and goldfish see the fatheads running for cover, they’re likely to do likewise and maybe avoid that heron or those pesky racoons.

Since they’re common bait and feeder fish, you can usually get them for about a dime apiece (or less). The downside is that they need to be quarantined for two weeks or more before going into a pond, since feeder fish aren’t usually raised in the most hygienic of conditions. But that’s easy to fix with some inexpensive quarantine methods. Elevated temperatures, higher salinity, or a little cheap medication can cover just about every common disease. Basically, the usual quarantine practices that most fishkeepers should be familiar with; it’s just more important than normal to use them with any bait/feeder fish.

Of course, another way to keep wildlife away from the pond would be to replace all the carp with an alligator gar. Then you’d find raccoon and heron bones in the pond instead of fish bones in the yard!

Carl Drews said:

Questions for the august company at Panda’s Thumb:

  1. Has anyone else observed similar examples of urban predation?

Yes, we used to keep goldfish in our pond, but cats and possibly raccoons kept eating them. One of my college professors recommended stocking ponds with gray goldfish and indigenous fish to keep visual predators from attacking pond fish.

  • Is this a valid example of differential predation and survival due to advantageous coloration?
  • This is a textbook example, in fact.

  • Do heron jab at their prey and pick them apart like hawks, or swallow the fish whole?
  • Herons and their relatives always swallow speared prey whole: they have no anatomical features to enable them to pick their prey apart. Captured prey is either speared, or caught ala chopstick/tonged style, then thrown or manipulated into the throat and swallowed.

  • Are Koi and goldfish the same species?
  • No, koi are domesticated strains of the Amur carp subspecies, Cyprinus carpio haematopterus, while the goldfish, Carassius auratus, is descended from yellow mutants of Prussian carp, Carassius gibelio, in China. While (female) goldfish are able to interbreed with other species of Eurasian carps, including koi, the offspring almost always wind up as clones of the mother, because if the goldfish’s freshly spawned egg is fertilized by the sperm of a related species, a mechanism in the egg then causes it to reject (usually) the father’s genetic contribution, and cause the egg to develop, anyhow. It’s one of the reasons why wild/escaped goldfish are considered vermin/pest species

    I was with my family at Disney World some years ago and we were at the entry to the African Savannah ride. There was a large fish pond there with a glass window on the side. To my astonishment the fish were East African cichlids, the ones that have been studied by evolutionary biologists. There seemed to be multiple species in there.

    To my greater astonishment the net covering the tank had some big holes, and some small herons had gotten in and were preying on the cichlids. I saw a staff member nearby. Hoping to stop this predation, I alled her attention to this. “Oh yeah,” she said, “they do that. We just toss more cichlids in.” So I guess they’re endangered in Florida too.

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    This page contains a single entry by Matt Young published on July 15, 2013 12:00 PM.

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