Evolutionary ecologist Bruce Lyon is back with another fact-filled post with great photos and his own videos. TRIGGER WARNING: consumption of mammals by birds is shown. I’ve indented Bruce’s commentary, and you can click on the photos to make them bigger.
Herons and egrets with interesting hunting strategies
Here in Coastal California pocket gophers (family Geomyidae) are abundant. These rodents are subterranean but easy to see because they often poke their heads up to the surface when digging burrows—they push dirt from tunnels out onto the ground. Pocket gophers are interesting for several reasons: they are important ecosystem engineers that affect the soil and plants, they destroy garden plants like nobody’s business, and they are a very abundant prey item for lots of predators. And they apparently get their name from fur-lined cheek pouches!
Below is a video of a local pocket gopher that has a collection of tunnels and surface mounds just outside my back door. I am not certain of the species but Botta’s pocket gopher (Thomomys bottae) seems most likely.
Pocket gophers can move a massive amount of earth: one estimate is 2 tons of soil brought to the surface per year per gopher. Since they can be very abundant, this can add up to a big effect at the landscape level. In coastal California, they can be hell on garden plants (they eat the roots), so gardeners often go to great lengths to protect their plants. One defense is a ‘gopher basket’—a wire basket lines a hole and then the plant and soil are put inside the basket. When we first bought our house, we did not always use gopher baskets and as a result lost a bunch of nice plants we had planted, including productive fig and lemon trees. We actually watched the lemon tree tip over and fall to the ground. When we checked it, it had no roots left.
Below: A gopher basket (photo from the web)
Gopher baskets are not the only line of defense—predators are another. Hawks, bobcats, coyotes, and even herons love to eat gophers. Great blue herons (Ardea herodias) have long hunted gophers in the fields around my house. Recently, a particularly tame heron has been hunting in peoples’ yards and because it is so tame I have been able to follow it around and observe and photograph it hunting gophers.
Below: Why did the heron cross the road? To gopher more food. [Example of appalling dad humor I try to inflict on my students.] This heron is right in front of my house.
Below: The heron slowly walks across a neighbor’s lawn after it has detected a gopher. I am not sure if the herons detect the gophers by hearing them moving near the surface or if they see the ground move when the gophers push soil up out of their burrow.
Below: The lunge. The technique is to stab the ground violently with the dagger-like beak. My impression is that they stab the gopher and wound or kill it with the stab. Note that the bird covers it eye with its transparent nictitating membrane during the stab. This translucent covering protects the eye from injury from branches or other sharp things that could damage the eyes.
Below: The attack was successful. This gopher was pretty large—they can get rat-sized. I watched this heron get five gophers in the space of a couple of hours! I suspect the gopher might have had a nest in the general area and was feeding kids.
Below: Another successful stab. This photo clearly shows that the animal had been impaled during the stabbing lunge.
Below: The herons swallow the gophers whole. Sometimes they toss them into the air, like popcorn, and then gulp them down. Other times they work them slowly up the beak to the mouth as this individual is doing.
Below: After several gophers, it is time for some relaxation and preening. Birds have a preen gland that produces waterproofing fats and lots of other goodies—the tip of this heron’s beak is right at the preen gland (on the lower back just where the tail feathers insert in the skin).
Great blue herons are not the only heron-like birds that have interesting hunting techniques. Tool use, foot shaking and providing shade (canopy hunting) have all been documented. Once in a while I see great egrets (Ardea alba) going for gophers but it is rare compared to herons Egrets have other tricks up their sleeves. One egret at my study area at the university arboretum learned that western fence lizards (Sceloporus occidentalis) are easy pickings, and I watched one egret pick off ten lizards in about 30 minutes. The egret was really tame so I was able to get a couple of videos with my phone. While hunting, the egret constantly swayed its neck back and forth, a behavior that has been discussed on WEIT before but I am not sure if we know why they do this.Below: Video of the great egret snatching a lizard. Note the swaying neck.
Below: Another video of the same bird.
Below: I have repeatedly seen snowy egrets (Egretta thula) catching fish in an interesting way at Jetty Road, a great birding spot south of Santa Cruz. A few large pipes go under the road to assist with tidal flow in Moss Landing Harbor. At certain tidal heights the water forms strong whirlpools and the egrets like to grab fish from the whirlpools. I am not sure if they do this because the fish are easier to see or if the whirlpool traps the fish so that cannot escape. Regardless, it is fun to watch. And note the bright yellow feet—this egret species sometimes hunts by shaking its feet in water and I have wondered if the yellow feet help with that in some way.
Below: This egret catches a grunion (Leuresthes tenius) at the whirlpool.
Excellent photos Bruce! I like the biology.
Bruce’s photos and commentary are always enjoyable.
Random thought: Gophers, and other burrowing critters, can wreak havoc on archaeological sites.
I need herons to keep the pocket gophers down. (Was trying to figure out how to move badgers in.) Have thought of gopher baskets but assumed they’d strangle the roots.
Awesome pics!
In addition to those mentioned, there is also the Bill Murray approach:
I’d think that the swaying (in the video more left to right than back and forth) refines depth perception with motion parallax.
This is a great idea. I think the egrets first detect the lizards when the lizards move but the lizards are mostly really still after detection. Perhaps the improved perception is needed to accurately locate a motionless prey? Or perhaps they are mesmerizing the lizards.
I enjoy the behaviors. So much to learn. So little time.
Yikes! I see a lot of blue herons, but did not know they could take mammals like that.
I don’t know why egrets have yellow feet. I’ve wondered if it helps distract fish from what’s below, so they don’t notice what’s going on above them.
I’ve watched herons hunt gophers in the field behind my house (Santa Barbara, CA). It was just like in the photos, except that when it came time to swallow, the heron extended its neck and beak straight up for a few seconds – very striking.
This is just a test.
Do you have time for this?
This is all about a special case of MIMICRY — you might want to read on.
I studied those bird videos & noted that the head of the bird moves something like a swaying vine or leaf.
Then it gets close enough & strikes.
Maybe 30 years ago I learned something about this swaying motion that some predators use.
I discovered how it seems to be ADAPTIVE.
I had these green bean vines growing over an arching arbor.
There were lots of insects visiting the vines, & not causing much if any harm.
And I kept finding little piles of grasshopper & beetle & bee parts under the arbor.
So, being of a liberal-&-curious persuasion, I started paying attention.
My innate need-for-discovery urges kicked in.
[Many of us bug-investigators enjoy this ADAPTIVE discovery-seeking quirk.]
More & more piles of mainly grasshopper bits appeared, with no predators in sight.
Finally, I got a chair & sat quietly to watch.
Soon, I spotted this biggish kind of blue-gray grasshopper amongst the maze of green pixilations.
After maybe a minute, it began moving again: they are very alert to any motion near them.
The only other motion in our immediate habitat was that of the bean leaves in the gentle breezes.
Soon, it was munching away, then moving on to another leaf.
That’s when I noted another motion in the all-green viney tableau, just inches away from the hopper!
What?
My mystified mind sought to resolve sense out of this all-green scene.
So, I waited — & then … something … moved again, with a swaying motion!
The swaying persisted for a few milli-seconds — & I suddenly resolved a triangular head with a pair of eyes.
It was a large green female praying mantis, slowly swaying closer & closer to the hopper!
Munch-munch-munch went the hopper, sway-sway-sway went the mantis.
The mantis got within 130 mm, then 75 mm, then 20 mm, then …
… it grabbed the hopper in mid-munch!
What did it all mean?
I think it means this — the mantis was ADAPTIVELY mimicking the motion of the leaves.
Prey species are innately very alert to any threat that comes straight at them.
Mantises, apparently, have evolved an ADAPTIVE work-around for this common problem.
But the proof is in the pudding — right?
So, I tried it out myself.
You can do it too.
Find a hopper munching away.
You can get quite close to many species before you violate their flight distance & they flee.
Approach slowly — & then slowly extend your hand off to one side.
Use a swaying, back-&-forth, right-&-left, up-&-down motion with your hand.
The shadow of your hand seems to make no difference — just like the shadow of a leaf would not matter.
It’s OK to feel stupid — maybe you should do this in private, like I did?
Maybe it helps to talk to the hopper, something like —
“… just a leaf in the breeze … nothing to worry about … just a leaf ….”
I still do that, & here it is decades later.
You can get your hand to within 3 or fewer inches [75 mm] of the hopper.
You spread your thumb & index finger to about an inch [25 mm] apart.
[Get a little closer & you can just gently poke the hopper! I am not making this up!]
Then, you just quickly reach & gently squeeze the little creature.
Then what?
Usually, I let em go.
I recall some research showing that produce from plants that have had some feeding damage are better for us.
It has to do with antioxidants produced being ADAPTIVE for us.
Thanks for the videos!
Cool discoveries!
Excellent pictures and narrative. Death by heron! Oh Death, there is thy sting!
Really enjoyed these pictures and the explanations. Thanks.
Damn! That’s brutal. It is like Jurassic Park. “Life for the gopher is hard and death comes quickly…a very stabby end to our furry friend….”
Also…. more insects please. The birds are great, but my favorites are those crazy bugs!
all the best and thx for the pix
D.A., NYC
Were that there were giant herons – giant enough to eat the groundhogs that I’m beset with. As it is, I think coyotes are my only hope. They’re in the area but don’t seem to have quite ventured into my urban setting yet, apparently finding enough to suit them up in the woods.