waders

Another Snowy Egret Fishing Technique

Gaping Snowy Egret at Elm Lake, Brazos Bend State Park.
Gaping Snowy Egret at Elm Lake, Brazos Bend State Park, Texas. This bird spent the morning on the shore shadowing Pied-billed Grebes as they hunted. Canon EOS 7D/600mm f/4L IS (+1.4x TC). Natural light.

Snowy Egrets are known for shuffling their bright yellow feet in the shallow water to scare up dinner. This summer I also caught one employing a bubble-blowing hunting technique to attract invertebrates and small fish.

On Saturday (11/2) at Elm Lake, Brazos Bend State Park, Texas I noticed another Snowy Egret fishing/hunting strategy that was new to me–and one that also involves scaring up prey. The egret shown above tracked Pied-billed Grebes back and forth as they chased fish and crawfish in the shallows, perhaps 3-4 feet from the shore. Likely fish and invertebrates scatter as grebes go swimming past–and likely this egret was making use of this to pick off prey responding to the grebes. During this shadowing behavior, the egret was quite good at predicting just where the grebe would surface. Perhaps the grebes were visible, at least sometimes, from the egret’s vantage point? Or was this wader ESP? In any case, the egret would often dash to a position on the shore closest to where the Grebe would suddenly emerge from the water.

Commensalism, a symbiosis in which one organism benefits and another is largely unaffected, is likely the label an ecologist would place on the above relationship. But could it be mutalism? Did the grebes benefit from the presence of the egret? Perhaps the egret could have revealed the presence of predators lurking in the shallows or the weeds? Did the grebes have one eye out on a friend on the shore who might signal (through behavior) the presence of an alligator lurking on the shore otherwise undetected? Or a nasty old alligator gar floating, log-like in the shallows? Perhaps the egret chased prey items (like plump juicy frogs) from the shoreline into the water? Food for thought.

Pied-billed Grebe with Red Swamp Crawfish at Elm Lake, Brazos Bend State Park.
Pied-billed Grebe with Red Swamp Crawfish at Elm Lake, Brazos Bend State Park. Note the large blob of water frozen in mid-air by high shutter speed as this grebe engaged in an epic struggle with a crawfish one-third its size. Canon EOS 7D/600mm f/L IS (+1.4x TC). Natural light.

Competition has been shown to be useful up to a certain point and no further, but cooperation, which is the thing we must strive for today, begins where competition leaves off.–FDR 

 ©2013 Christopher R. Cunningham. All rights reserved. No text or images may be duplicated or distributed without permission.

Waders Will Continue to Surprise the Attentive Birder with Diverse Hunting and Fishing Strategies

Crouching Green Heron at Brazos Bend State Park, Texas
Green Heron Crouching Low on American Lotus Leaf. Perhaps to remain invisible to fish swimming near the surface, this Green Heron rested on its toes and feet close to water level. Canon EOS 7D/600mm f/4L IS (+1.4x TC). Elm Lake, Brazos Bend State Park, Texas, natural light.

Even after several years of frequent wader-watching at Brazos Bend, these birds continue to reveal new tricks in their extensive repertoire of hunting strategies. Recently I observed a Green Heron resting on an American Lotus leaf. Green Herons are common at Brazos Bend, and they can often be seen hunting and fishing from aquatic vegetation and partly submerged logs. Birds usually stand on their toes. What was interesting in this case was that the bird was crouching low, resting on its toes and feet (digits and tarsometatarsi, respectively) near the edge of the plant. The bird peeked over the edge of the leaf, studied the surface of the water, and every so often shot out its long neck and snatched a small fish from near the surface of the water. Was the bird hiding from the fish below or studying the fish-produced ripples on the surface of the water, or both? In any case, it was fun to watch.

Nitpicking Green Heron at Brazos Bend State Park, Texas
Nitpicking Green Heron at Elm Lake, Brazos Bend State Park, Texas. Canon EOS 7D/600mm f/4L IS (+1.4x TC).

Waders are great preeners, constantly cleaning and fussing with their feathers. Usually preening means that the action is over for a while–so the photographer interested in capturing hunting and fishing scenes may just as well move on to another bird. However, this summer I caught a Green Heron using the brilliant sunlight to find snacks on its wings. The bird, shown above, held its wings up to the sun. The light streaming through the feathers presumably allowed the bird to spot parasites, pick them off, and eat them. Pretty neat: dining at home!

Snowy Egret bubbling and crouching at Brazos Bend State Park, Texas
Snowy Egret Bubbling and Crouching at Brazos Bend State Park, Texas. This bird is blowing bubbles and making ripples that seem to attract prey, including fish. In this case, the egret is crouching with one foot on a submerged log, the other on the bottom. Canon EOS 7D/600mm f/4L IS (+1.4x TC). High-speed synchronized fill-flash.

This summer at least one Snowy Egret spent a lot of time blowing bubbles (and making ripples). This bubbling clearly activity attracted a variety of prey, mostly small fish, that were quickly snapped up. Once, the bubbling attracted something that was too big to handle. I saw a disturbance in the water, and the bird ran away squawking–perhaps a big gar or bowfin came slithering up? I also caught a bubbling Snowy Egret resting on its toes and feet on a log (shown below).

A Snowy Egret rests on its tarsometatarsi to hunt at Brazos Bend State Park, Texas
Crouching Snowy Egret. This Snowy Egret rests on its feet and toes to hunt via bubble-blowing at Brazos Bend State Park, Texas. A few bubbles can still be seen on the surface of the water. Canon EOS 7D/600mm f/4L IS (+1.4x TC).

Although wary and uncooperative photographic subjects, Cattle Egrets are common in the grassy areas–and occasionally at the waters’ edge–at Brazos Bend. One day I saw a group of half a dozen Cattle Egrets stalking through the brush like a gang of young toughs grabbing dragonflies and spiders and whatever else moved. They strolled along together, a few feet apart, though the understory vegetation. If one bird flushed or disturbed a prey item an adjacent bird got a crack at it. Grasshoppers, spiders, dragonflies, maybe the occasional frog–down the hatch! Co-operation: it works!

Cattle Egret at Brazos Bend State Park, Texas
Cattle Egret Hunting Dragonflies and Spiders at Brazos Bend State Park. Photo taken at Pilant Slough. Canon EOS 7D/600mm f/4L IS (+1.4x TC). High-speed synchronized fill-flash.

There’s a fine line between fishing and just standing  on the shore like an idiot.—Steven Wright

©2013 Christopher R. Cunningham. All rights reserved. No text or images may be duplicated or distributed without permission.

A Diversity of Menu Items for Waders at Brazos Bend State Park, Texas

Green Heron with Fishing Spider at Brazos Bend State Park, Texas.
Green Heron with Six-spotted Fishing Spider (Dolomedes triton) at Brazos Bend State Park. Photo taken near Pilant Slough. Canon EOS 7D/600mm f/4L IS (+1.4x TC). High-speed synchronized flash.

There has been a bumper crop of fishing spiders this year at Brazos Bend State Park, and I have seen Little Blue Herons and Green Herons eat them, sometimes one spider right after another. Some years it seems as though wader diets consist of a fairly uniform mix of aquatic vertebrates and invertebrates, especially crawfish. This year, rather than crawfish, waders seem to be relying more heavily on smaller invertebrate prey items than in recent years. Lots of aquatic insect larvae, dragonflies, adult aquatic bugs and beetles, and spiders are being consumed along with the occasional small fish, frog, or tadpole.

Little Blue Heron with Dragonfly
Juvenile Little Blue Heron with Swift Long-winged Skimmer Dragonfly (Pachydiplax longipennis) at 40-Acre Lake, Brazos Bend State Park, Texas. Juvenile Little Blue Herons are fun to stalk: they are prolific hunters but, being young, they still have a level of naiveté toward humans allowing a close approach. Canon EOS 7D/600mm f/4L IS. High-speed synchronized fill-flash.

Invertebrates are highly sensitive to environmental conditions of temperature, humidity, and rainfall. This year’s unusually cool, dry spring may have led to a different mix of potential prey for waders. The Upper Texas Gulf Coast is already behind in rainfall for the summer and water levels already appear low, perhaps impacting aquatic vertebrate numbers as well.

Many of the invertebrates (spiders especially) I see waders take are living among the Water Hyacinth that is growing profusely in some areas of the park. Water Hyacinth is native to the Amazon Basin, but has been imported to many areas of the world where it has become a major nuisance by crowding out and shading native plants and choking waterways.

Water Hyacinth at Brazos Bend State Park, Texas
Beautiful Invasive: Common Water Hyacinth (Eichhornia crassipes) at Brazos Bend State Park. Water Hyacinth is costly and troublesome for land managers. Mechanical, chemical, and biological mechanisms for its control have been devised and employed worldwide.

Besides keeping an eye (and a lens) out for interesting wader predator-prey relationships, I am always on the look-out for hunting techniques. For example, Snowy Egrets are known for shuffling their bright yellow feet in the shallows to flush out prey. Several times over the past weeks I have seen a Snowy Egret (I think it was the same bird) employing a bubble-blowing technique on Elm Lake. This bird was (presumably) blowing bubbles to attract prey. Perhaps the bubbling simulates a small struggling animal, attractive to fish and other aquatic predators. Between bouts of bubbling, this bird also opened and closed its beak, a fishing technique I have seen employed by Black-crowned Night-Herons and Great Egrets, and one that also sends ripples out into the water. One time during this process this Snowy Egret grabbed a small aquatic invertebrate–it was down the hatch too fast to tell for sure what it was, although it was about the right size and shape for a water tiger (larval predaceous diving beetle). On another occasion, the egret was clearly catching small fish with this technique. Time will tell if anything bigger can be attracted by blowing bubbles!

Snowy Egret blowing bubbles at Brazos Bend State Park, Texas
Snowy Egret Blowing Bubbles at Brazos Bend State Park, Texas. Photo taken at Elm Lake. Canon EOS 7D/600mm f/4L IS. High-speed synchronized flash.

©2013 Christopher R. Cunningham. All rights reserved. No text or images may be duplicated or distributed without permission.

Instinctive Behavior in a Green Heron, Brazos Bend State Park, Texas

What a book a devil’s chaplain might write on the clumsy, wasteful, blundering, low, and horribly cruel work of nature! –Charles Darwin

Usually when one sees a wader grab a prey item, the prey is subdued, perhaps by a few pecks, then manipulated into position and swallowed. Today at Brazos Bend State Park, however, I observed a Green Heron grab a large American Bullfrog tadpole. The bird picked up and then dropped the tadpole a few times after intermittently pecking it. Finally the bird discarded the tadpole and walked away. I thought this strange given that waders of all species at Brazos Bend eagerly consume amphibians in all stages of development. Perhaps (although it seemed unlikely) the bird considered the tadpole to be too big to swallow?

I continued to watch the Green Heron fully expecting the bird to reconsider and return to the tadpole and eat it. Instead, it caught a juvenile frog and repeated the whole process! After pecking the poor frog a few times, the Green Heron just walked off without eating it. I have only seen this sort of thing once before when a Little Blue Heron captured and then discarded a crawfish. Do these waders hunt and kill (or at least maim) instinctively without being hungry, and without lardering the prey–just like well-fed house cats? If so, stone cold killers, these fellows!

Green Heron with juvenile frog at Brazos Bend State Park, Texas
Bad Day at Elm Lake: this Green Heron captured, subdued, beaked, and then discarded without eating this unfortunate frog. Canon EOS 7D/500mm f/4L IS (+1.4x TC). High-speed synchronized fill-flash.

©2012 Christopher R. Cunningham. All rights reserved. No text or images may be duplicated or distributed without permission.