1984 | Kumamoto, Japan
Green-backed heron (Butorides striatus) bait fishing
Suizen-ji Park in Kumamoto is an oasis of calm, especially during the hot, humid summers. Located on Japan’s southerly island of Kyushu, just a short walk from Kumamoto Castle, for almost 400 years the park has attracted visitors and locals with its landscaped lawns, bridges and replica of Mount Fuji. In the summer of 1984, however, Hiroyoshi Higuchi was interested in a different kind of attraction. The birds were fishing, and they were using bait.
During the summer, a couple of dozen green-backed herons use Suizen-ji Park’s pond as their main feeding grounds. The pond covers more than a tenth of the park, and contains a variety of fish, from carp (Cyprinus carpio) to dace (Tribolodon hakonensis) and pale chub (Zacco platypus). Over several days, Higuchi patiently sat and watched as the birds approached the edge of the water.
Fishing herons first find shallow water, and very carefully position themselves within striking distance. Then they crouch, and freeze. It is an ambush, waiting for a tasty fish to swim to the perfect position before the heron extends their neck in a lightning strike forwards and down into the water. Success is marked by emergence with a struggling captive in their beak. Provided enough fish swim by, the hunt goes well.
Taking the bait
On its own, watching herons fish is a pleasant enough way to spend a summer’s afternoon in Kumamoto. What interested Higuchi, though, was how the herons looked to twist the odds in their favour. Often a heron would arrive at a fishing site, and instead of settling in to wait, it would first cast around for an object.
Berries, insects, twigs, leaves and more—none of them food for the bird itself—were dug up or plucked from the nearby rocky pond banks. After assessing local fish activity, the heron then placed the selected object on the surface of the water, within striking distance. If it drifted, they would occasionally re-position it. The intention was clear: attract more fish using bait.
The results speak for themselves. Over a roughly hour-long period, two herons caught seven fish using bait, and only one fish without. Insects were the most successful type of bait, attracting fish in under 5 seconds on average, with flies and other adult insects the top draws. Twigs and berries worked too, although on average it took more than twice as long for a successful capture using plant rather than animal bait.
Adult herons were much more successful at bait fishing than younger birds, which Higuchi linked to poor juvenile technique (not having mastered the crouch and freeze), and choosing objects too large to attract the fish. Remarkably, twice an adult heron actually shortened a twig before using it, clipping it to a better length using its beak. They were not just using, but making tools.
As Higuchi noted, he was not the first to record heron-bait-fishing, and nor was he the last. A 1998 review by William Davis and Julie Zickfoose found that green-backed or striated herons, and their close North American relative the green heron (Butorides virescens) had been spotted bait-fishing in east, west and southern Africa, the USA, and in Peru. In all cases the behaviour is very similar: selection or manufacture of a small lure, dropping it precisely within striking distance, and patiently waiting until an unsuspecting fish investigates.
Cost-cutting
What wider conclusions can we draw from this behaviour? Are baiting herons ‘smarter’ in some way that other birds may not be? Graeme Ruxton and Michael Hansell considered just those questions in a 2011 summary in the journal Ethology. They concluded that the relative rarity of the behaviour, and its concentration around the heron family, meant that:
either bait fishing is rarely cost-effective in comparison to alternative foraging tactics, or it is cognitively challenging and only effective when practiced by a select few individuals.
The first of these hypotheses is built on the fact that gathering bait costs energy, however little, and moving bait around diminishes the effectiveness of the crouch and freeze ambush tactic. Bait-fishing should only be used where it brings in more fish than the non-tool-use alternative.
The second idea is the one mentioned above, that there is a kind of mental agility required to identify, capture and precisely position bait on the water, as an intermediate step that may actually add time between the start of the hunt and the capture of a fish. It could imply planning, or a mental model in which the bird knows what the fish sees as bait, and hijacks that fishy instinct.
At this point, neither of these hypotheses have enough evidence. The first, environmental one could be tested by accurately comparing energy returns in a natural setting from fishing with and without bait. The second, cognitive one could be tested by seeing whether animals that are more successful at bait fishing are also more inventive or successful at other challenging tasks in their daily lives.
As Ruxton and Hansell note, the fact that some herons made lures—rather than just collecting them—could be possible evidence for particular ingenuity, or simply the common level of dexterity often shown by nest-making birds.
Humans have taken fishing to an extreme. In many cases we no longer even need lures or bait, just a trawler, knowledge of fish migration patterns, sonar and a huge net. However, the tale of the bait-fishing herons in the shadow of their miniature Mt Fuji is not one to be compared with mechanised industrial fishing fleets. Instead, it should remind us of the fact that individual people, all around the world, are routinely less effective at luring and catching individual fish than a small, patient bird.
Sources: Higuchi, H. (1986) Bait-fishing by the Green-backed Heron Ardeola striata in Japan. Ibis 128:285-290. || Davis, W. & J. Zickfoose (1998) Bait-fishing by birds: a fascinating example of tool-use. Bird Observer 26: 139-143. || Ruxtone, G. & M. Hansell (2011) Fishing with a Bait or Lure: A Brief Review of the Cognitive Issues. Ethology 117: 1-9.
Main image credit: http://morgithology.blogspot.com/