2019 | Saigon Botanical Gardens, Vietnam
Black-crowned night heron (Nycticorax nycticorax) twig fishing
January’s namesake, the Roman god Janus, looks forward and backwards at the same time. It’s a handy skill for the god of doorways and transitions, and a natural fit for the start of a new year. For this first post of 2023, therefore, I pay my respects to Janus by looking back, and revisiting the very first tool-using animal that I wrote about on this blog. It’s not one that most people think of when this topic comes up, though: neither a nimble chimpanzee nor a wily monkey, or even a clever crow. It’s a heron.
My original post back in 2020 followed the work of Hiroyoshi Higuchi in Kyushu, Japan. As Higuchi patiently watched, a green-backed or striated heron (Butorides striata) carefully placed a variety of objects onto the surface of a pond, aiming to entice curious nearby fish into having a closer look at this possible meal. Meanwhile the bird froze into an intent death stare. Finally, with whip-crack speed and precise binocular vision, the heron extended its neck and grabbed any fish unlucky enough to get within range.
Tool use is relatively uncommon in the animal kingdom, but it does show up as clusters around certain related species. For example, many decorator crab species apply sponges and other material as camouflage to their shells, and a number of myrmicine ant species in the genus Apaenogaster have been seen using bits of plant and soil matter to absorb and carry liquids. Our own closest relatives, the great apes—orangutans, gorillas, chimpanzees and bonobos—provide another example of a tool-use cluster, which naturally includes us humans too. And it turns out that some herons are the same, especially when it comes to bait-fishing.
Today, then, we’re looking at a close cousin of the green-backed heron, the fantastically named black-crowned night heron (Nycticorax nycticorax). And from Japan we’re taking a short trip south, to the Saigon Botanical Gardens in Ho Chi Minh City, Vietnam.
A snappy response
We’re in Saigon thanks to a recent report published by Blanton Paul Combs and Michel Antoine Réglade. In mid-November 2019, Combs was visiting the large goldfish pond at the botanical gardens, when he noticed a particular sub-adult bird near the water’s edge. That’s it in the photo at the top of this post, and here it is again:
In both photos, the heron-eyed among you will have spotted the small brown stick held in the bird’s beak. That stick was originally sitting on the muddy bank, and you can see it in that position in this additional photo from Combs and Réglade’s 2022 paper in the Journal of Heron Biology and Conservation. Just follow the pointy arrow of the heron’s bill and you’ll see the twig lying there, which the study describes as ‘about the size of an average cigarette’:
Over a period of several minutes, the heron used the stick as a lure to bring fish towards its ambush. From the paper:
it stepped out of the water and onto the bank, turned around, and dropped or tossed the twig onto the surface of the pond. The heron retrieved the twig and dropped it into the water several more times. Each time the heron dropped the twig into the water, it stood motionless and watched the twig closely for up to 30 seconds. Ripples and swirls appeared on the calm surface of the pond near the twig, indicating that fish had begun to investigate it.
This kind of behaviour, using an object to manipulate the environment, falls under typical definitions of tool use. Recently some researchers have focused more closely on tools as being things used solely as mechanical drivers—for example as levers or other means of exerting direct force—which wouldn’t cover this heron’s bait fishing activity. However, in a broader perspective the bird’s use of an external object to achieve a goal makes this a fairly clear-cut technological task.
The Saigon night heron managed to grab hold of one fish attracted to its sticky lure, although it couldn’t hang on and the catch got away. (Later the bird probably described the lost fish to its heron friends as being ‘seriously, this big’ while stretching its wings to their fullest extent.) Shortly afterwards, it picked up the twig and moved to a new location, out of sight of Combs and his camera, just as a human might pack up and carry their rod to find a better spot:
Fishing with dragons
The Vietnam report is the first time that a black-crowned night heron has been filmed bait fishing with an inedible lure. The fact that sticks aren’t bird food makes it even easier to recognise tool use, because we can rule out the possibility that the heron was trying to eat the twig and accidentally dropped it several times while doing so.
Nevertheless, it’s a little frustrating (for us and the bird) that the researchers didn't get to see it succeed with a fishy meal. Luckily, another study by Michel Antoine Réglade from 2014 can help us out. In that report, Réglade’s colleagues filmed a second sub-adult night heron, this time all the way across the Pacific on Lake Tinquilco in Chile.
Perched on a branch just above the lake edge, the Chilean bird had plenty of sticks to use as lures if it wanted. However, it also had a more natural bait: dragonflies. For about an hour Daniela Siel and Manuel Uribe filmed the heron catching, repositioning and monitoring dragonflies that it placed on the surface of the lake. I’ve extracted a couple of sections from their full video to include in this post, to give you an idea of how this crafty bird went about its work.
A heads up: the video was filmed by hand in February 2006 from an inflatable boat on the lake. It has lower quality than more modern films and a fair bit of movement. I’ve chosen sections that minimise this movement, but I couldn’t avoid it altogether. I don’t blame the researchers at all—from my own experience filming wild monkeys from a boat in Thailand I know this is a difficult job. It’s worth watching, I promise.
In the first video, we see the heron in its characteristic frozen hunting pose, before it successfully snaps up a fish from beneath the surface and swallows it down. Seconds later, it snatches a passing dragonfly out of the air. It then uses the insect to agitate the surface of the water, incapacitating the dragonfly at the same time:
With its bait secured, the heron carefully places it onto the water. It then sits back, its head turning slightly to each side as it tracks the potential prey that swim by to investigate. Finally, it makes two swift strikes in succession, each bringing up another fishy treat:
The final sequence we’ll look at is slightly longer. It starts with a missed strike on a fish, before the heron reaches across to grab the dragonfly bait that has drifted away from its original position. Then follows a prolonged bout of baiting—the dragonfly is repeatedly dipped into and out of the water. While in the water, the heron uses its beak to create bursts of ripples, perhaps mimicking the struggles of a downed insect (that’s speculation, not confirmed fact).
Eventually, after yet more patient observation, the bird makes another successful catch:
The authors of the Chilean report suggest that the heron wasn’t just plopping the dragonfly down in any old spot, but rather it was attempting to maximise its catch:
It is interesting to note that the movements of the heron’s head often preceded the beginning of the bait positioning. This suggests that the heron looked carefully at prey movements before “deciding” when and how to place the bait in order to optimize the probability of a successful capture.
Clearly the strategy—whatever it actually was—worked. The night heron was more successful fishing with insect bait than without, capturing 10 fish in 20 minutes using a dragonfly, versus one fish in 10 minutes without bait. A single bird or fishing bout obviously can’t tell us for sure just how much better a lure is, but it’s a useful baseline for comparing any future observations.
As always, we should be careful before concluding that any given behaviour definitely is tool-use, instead of some other kind of object manipulation. For example, one possibility considered in the 2022 Vietnam study is that the photographed heron was simply playing with a stick, and not actively fishing at all. The researchers draw on previous work on play by herons to suggest that it has five main characteristics:
(1) - Play is repetitive, awkward, or exaggerated.
(2) - Play lacks a final consummatory act [i.e. there is no final goal].
(3) - Play is incomplete or in reordered sequences.
(4) - Play has no obvious immediate function.
(5) - Play is quick and energetically expensive.
Since the Saigon bird was not yet fully adult, play is definitely a factor to consider. However, the authors conclude that the deliberate, patient, careful nature of the twig baiting they saw rules out play. For instance, once it had collected the stick, the night heron didn’t move its feet as it positioned and repositioned the bait, and made its one (ultimately unsuccessful) strike. That’s not what you’d expect from an excitable and undirected play activity.
The fact that we’re revisiting heron baiting on the blog shows that our knowledge of this behaviour continues to grow. However, these examples also clearly demonstrate that there is still much to learn about when, how and why herons use tools. Fortunately, night herons are a globally widespread species, and we know that other closely-related heron species also fish with bait. It’s a common refrain here, but once again I can only urge you to keep an eye out around the ponds and lakes in your neighbourhood. The next big tool-use discovery could be yours!
Further viewing
The full 30 minute video of a sub-adult black-crowned night heron fishing with dragonfly bait, from the 2014 study by Michel Antoine Réglade and colleagues, is available via this youtube link. If instead you’d like to just watch an adult night heron catching fish after fish with casual ease—no bait required—check out the skills of this bird filmed by Stoil Ivanov in 2020 in Illinois, USA:
Sources: Combs, B. & M.A. Réglade (2022) Black-crowned Night Heron (Nycticorax nycticorax) bait-fishes with an inedible lure in Vietnam. Journal of Heron Biology and Conservation 7:5. || Réglade, M.A., D. Siel & M. Uribe (2014) Bait-fishing black-crowned night heron (Nycticorax nycticorax) in Chile. Ornitologia Neotropical 25: 465-468.
Main image credit: Combs & Réglade 2022, Fig. 4 || Second to fourth image credits: Combs & Réglade 2022 || First to third video credits: Réglade et al. 2014; https://www.youtube.com/watch?v=3R0X_M-dHSw || Final video credit: Stoil Ivanov; https://www.youtube.com/watch?v=rbcCh7TYNKc