Copyright © 2022. Combs, Blanton Paul and Michel Antoine Réglade. 2022. Blackcrowned Night Heron (Nycticorax nycticorax) bait-fishes with an inedible lure in Vietnam.
Journal of Heron Biology and Conservation 7:5 [online] www.HeronConservation.org/
JHBC/vol07/art05/

Black-crowned Night Heron (Nycticorax nycticorax) bait-fishes with aninedible lure in Vietnam
Blanton Paul Combs1* and Michel Antoine Réglade2
1 193 Glen Dale Drive, Woodland Park, Colorado, U.S.A.; combsbp@gmail.com
2 18 rue de Garin, 31500, Toulouse, France; reglade@hotmail.fr*Primary contact
Abstract
Since 1996, Black-crowned Night Herons (Nycticorax nycticorax) have been noted to bait-fish on several
continents and islands, but always with edible baits, such as insects or bread. After a careful search of theliterature, this paper asserts that it is the first report, with photographs, of any member of this species baitfishing with an inedible lure, namely, a short twig.
Key words: active bait-fishing, animal tool use, inedible lure, Nycticorax nycticorax.

Introduction
Tool use in animals has been defined as “actuallywielding some external object as an implement”(Thomson 1964), but it has only been documented
in fewer than 1% of animal genera (Visalberghi etal. 2017). This makes bait-fishing by birds highlyinteresting for animal behaviorists because, forsome of them, it fits the established criteria fortool use (Crain et al. 2013). Ruxton and Hansell(2011) established useful criteria for bait-fishingwhen they wrote that active bait-fishing occurs
when a bird places an edible (bait) or inedible(lure) item within its striking range in order to attract or distract potential prey fish. Passive baitfishing, on the other hand, occurs when a bird forages near bait that is already on the water andwithout manipulating it, such as bread tossed byhumans. Despite numerous reports that cite bothactive and passive bait-fishing with edible bait byBlack-crowned Night Herons, there have been noreports of bait-fishing with an inedible lure. This
paper asserts that it is the first to report, with photographic evidence, bait-fishing by a subadultBlack-crowned Night Heron (Nycticorax nycticorax) with an inedible lure.
Observation
On 14 November 2019, BPC was visiting theSaigon Botanical Gardens in Ho Chi Minh City,Thanh Pho Ho Chi Minh Province, Vietnam, 10°47′ 10″ N, 106° 42′ 25″ E. The gardens have alarge pond with goldfish (probably Carassius au-Journal of Heron Biology and Conservation 7:5, page 2ratus). The pond surrounds a wooded island thatseveral species of piscivorous birds use for foraging, resting and breeding, including Common
Kingfishers (Alcedo atthis), Black-headed Ibises(Threskiornis melanocephalus), Great Egrets(Ardea alba), Lesser Adjutant Storks (Leptoptilosjavanicus), Painted Storks (Mycteria leucocephala), an unidentified Pond Heron (Ardeolasp.) and Black-crowned Night Herons.
The birds also nest, rest and preen on the nearbybuildings and trees. Except for a few injured andnon-volant storks, the bird population at the pond
is wild.
At about 10:00 hr, BPC began to photograph asubadult Black-crowned Night Heron that was
foraging by Slow-Wading (Meyerriecks 1960)
around the perimeter of the island. The heron used

its beak to pick up a twig about 8 cm long andnearly 1 cm thick, or about the size of an averagecigarette (Fig. 1). The heron did not attempt tomodify the twig.
BPC continued to photograph the heron while it
stepped out of the water and onto the bank, turned
around, and dropped or tossed the twig onto thesurface of the pond. (Fig. 2). The heron retrieved
the twig and dropped it into the water several
more times (Fig. 3). Each time the heron dropped
the twig into the water, it stood motionless andwatched the twig closely for up to 30 seconds.
Ripples and swirls appeared on the calm surfaceof the pond near the twig, indicating that fish had
begun to investigate it.
This activity continued for about three minutes.
An examination of the attached photographs

Figure 1. Subadult Black-crowned Night Heron is foraging by Slow Wading. Seconds later, it picked up the twig at theedge of the water and began to use it for active bait-fishing. Saigon Botanical Gardens, Vietnam, 14 November 2019.

Journal of Heron Biology and Conservation 7:5, page 3

Figure 2. Subadult Black-crowned Night Heron has seized the twig in its beak, climbed the bank,turned around, and is preparing to drop it into the water for active bait-fishing. Saigon Botanical
Gardens, Vietnam, 14 November 2019.

Figure 3. Subadult Black-crowned Night Heron has dropped its twig lure into the water to use it for
active bait-fishing (note ripples). Saigon Botanical Gardens, Vietnam, 14 November 2019.

Journal of Heron Biology and Conservation 7:5, page 4shows that the heron did not move either foot during the entire time it stood on the bank. The heron
only moved its head briefly when it needed to reposition the lure because it had begun to drift beyond striking range. The heron struck once at afish and held it briefly, but could not subdue it. The
struggling fish created splashes which were audible to BPC, who was approximately 30 m away.
After the failed strike, and after the heron had
dropped the twig lure onto the water several moretimes (Figs. 4 and 5), it reentered the water, retrieved the lure in its beak, and carried it about 10m around the shore of the island (Fig. 6). This portion of the shore is concealed by leafy, overhanging branches. Once the heron had positioned itself
behind the foliage, it appeared to resume bait-fishing, but it was impossible to obtain clear photographs of the heron’s activity from any angle.

Discussion
McCullough and Beasley (1996) were the first toreport a Black-crowned Night Heron foraging byactive bait-fishing with bread in California, USA,followed by Riehl (2001) in Louisiana, USA, andthree reports from Hawaii, USA: Gavin andSolomon (2009), Walther (2009) and Pratt et al.
(2011). These reports have been followed by others and they describe Black-crowned Night
Herons using both passive and active bait-fishingwith bread or other food that had been supplied byhumans. Réglade et al. (2014) were the first to report, with video footage, a subadult Blackcrowned Night Heron in Chile foraging by active
bait-fishing with dragonflies as edible bait andwithout any apparent interaction with humans.
During their observation, the heron successfullycaught and consumed several small fish after it

Figure 4. Subadult Black-crowned Night Heron has retrieved its twig lure from the water’s surface (note ripples) andis preparing to drop it again to resume active bait-fishing. Saigon Botanical Gardens, Vietnam, 14 November 2019.

Journal of Heron Biology and Conservation 7:5, page 5

Figure 5. Sub-adult Black-crowned Night Heron tosses its twig lure in a new direction. Saigon BotanicalGardens, Vietnam, 14 November 2019.

Figure 6. After a few minutes of bait-fishing and an unsuccessful strike at a large fish, the heron reenters the water, retrieves its twig lure, and carries it to a new location to resume active bait-fishing.
Saigon Botanical Gardens, Vietnam, 14 November 2019.

Journal of Heron Biology and Conservation 7:5, page 6

had caught dragonflies and placed them on the water’s surface, one at a time. Our report is the firstto document a subadult Black-crowned Night
Heron engaging in active bait-fishing with aninedible lure, namely a short stick. This reportmakes the Black-crowned Night Heron the third
most well-documented species of active bait-fishing ardeid after the Green Heron (Norris 1975,Higuchi 1988) and the Striated Heron (Higuchi1986).
But because the subject is a subadult bird, there
could be an alternative explanation, which is“play,” sometimes called “play-learning” behavior.
In his detailed paper, Sazima (2008) writes thatplay is widespread among juvenile and subadultmembers of Ardeidae and that it is commonly “regarded as having an important role in general motor development and for practice of particularskills, mostly foraging and breeding.” Sazima
goes on to describe how juvenile members ofArdeidae play with small pieces of wood, fruit andother floating objects, which they repeatedly toss
into water. This activity contributes to the development of the skills required for bait-fishing,which is common among ardeids (Ruxton andHansell 2011). Sazima includes the following behavioral criteria within play:(1) - Play is repetitive, awkward, or exaggerated.
(2) - Play lacks a final consummatory act.
(3) - Play is incomplete or in reordered sequences.
(4) - Play has no obvious immediate function.
(5) - Play is quick and energetically expensive.
Without justifying precisely each of them, it iseasy to admit that none of these five criteria can beapplied to our observation.
Two examples of play-learning that fit Sazima’scriteria:(1) – Early play-learning stage. On 14 April 2019,at Lac du Val de Saune, Sainte Foy d’Aigrefeuille,
France (43° 32′ 50″ N, 1° 36′ 30″ E), Ghislain
Riou, a professional ornithologist, observed animmature Black-crowned Night Heron playing ona pond edge. In his description, “The excited bird
appeared to be briskly chasing twigs and small
branches on the surface of the water, grabbing
them and sometimes pushing them a few feetaway but without any other aspect of the bait fishing sequence.” (G. Riou, pers. comm., 14 April2019). This description contains all five of Sazima’s criteria for play.
(2) – More advanced play-learning stage. It can bedifficult to determine whether an activity constitutes play-learning behavior, a serious attempt at
bait-fishing, or an intermediate stage. There is an85-second video from Hong Kong, showing anadult Black-crowned Night Heron at an intermediate learning stage (birdvideo123 2014). It shows
the bird stopping to retrieve a floating stick about
20 cm long. It picked up and dropped the stick six
times in rapid succession in what could be apoorly-developed bait-fishing technique. It istempting, since the heron in the video is an adult,
to assume that it is bait-fishing, especially because
its behavior is fairly deliberate, and not exuberantor random. But it is obviously unclear about
where to place the stick, or for how long. No clear
strike occurs and no fish is caught. This sequence
resembles the idea that we have, a priori, of an intermediate learning stage, but this interesting sequence is too brief to definitively decide theprecise category of the behavior. It might be an example of an intermediate learning stage or justplay with a stick.
It appears to be important that field ornithologists
should acquaint themselves with these different
behaviors in order to be able to distinguish amongplay, intermediate learning stages, and well-characterized bait-fishing behavior. We suggest that
continued reporting of such observations is theJournal of Heron Biology and Conservation 7:5, page 7

best method to improve our knowledge of this intriguing behavior. The roles of innate and acquired
knowledge and the evolution of the underlying
cognitive abilities implicated in this remarkablebehavior remain interesting topics to explore.

cens) using feather lure for fishing. AmericanBirds 29: 652-654.
Pratt, H. D., J. Denis, M. Walther and C. Walther.
2011. Rapid and widespread appearance of baitfishing, a form of tool use, by Black-Crowned
Night Herons in Hawai’i. ‘Elepaio 71: 24-28.

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