Active and passive bait-fishing by Black-crowned Night Herons.
Abstract: Previous research reports bait-fishing in seven different species of ardeids. Our observations of Black-crowned Night Herons (Nycticorax nycticorax) on the island of Oahu, Hawaii, USA are the first to detail both passive and active bait-fishing in the same species. These observations provide support for the hypothesis that passive bait-fishing is a precursor to development of active bait-fishing methods in wading birds.
Article Type: Report
Subject: Foraging (Research)
Authors: Gavin, Michael C.
Solomon, Jennifer N.
Pub Date: 12/01/2009
Publication: Name: The Wilson Journal of Ornithology Publisher: Wilson Ornithological Society Audience: Academic Format: Magazine/Journal Subject: Biological sciences Copyright: COPYRIGHT 2009 Wilson Ornithological Society ISSN: 1559-4491
Issue: Date: Dec, 2009 Source Volume: 121 Source Issue: 4
Topic: Event Code: 310 Science & research
Geographic: Geographic Scope: Hawaii Geographic Code: 1U9HI Hawaii
Accession Number: 216267559
Full Text: Multiple species of ardeids catch fish using bait. Active bait-fishing involves birds identifying and placing bait (e.g., bread, insects) into water to attract fish. For example, Green Herons (Butorides virescens) (Keenan 1981) and Squacco Herons (Ardeola ralloides) (Crous 1994) actively fish with insects as bait. Striated Herons (Butorides striata), Green Herons, and Goliath Herons (Ardea goliath) also actively fish with artificial lures (e.g., flowers, feathers, sticks) (Norris 1975, Higuchi 1986, Hunter et al. 2004). In contrast, studies report Great Egrets (A. alba) (Lovell 1958) and Great Blue Herons (A. herodias) (Zickefoose and Davis 1998) passively use bait to catch fish. Passive bait-fishing involves birds waiting by bait to catch fish, but not actively placing bait in the water themselves or actively manipulating the bait.

Based on simultaneous observations of a Green Heron actively bait-fishing and a Great Egret passively bait-fishing, Lovell (1958) suggested that passive techniques are critical precursors to development of active bait-fishing ability. However, prior to our observations, no studies have reported both active and passive bait-fishing in the same species.

OBSERVATIONS

We encountered an adult Black-crowned Night Heron (Nycticorax nycticorax) on 6 January 2009 foraging at the edge of a pond on the eastern end of Ala Moana Beach Park in Honolulu, Hawaii. A passer-by was throwing bread to fish in the pond. When bread landed in front of the heron, either in the water or on shore, the bird did not eat the bread. The heron waded in among the bread and moved its head from side to side watching fish gather to feed on the bread. Over a 10-min period the bird caught three fish. After each catch the heron returned to shore to eat the fish and then waited for more bread to be thrown before it waded back into the water.

We again encountered a Black-crowned Night Heron on 7 January 2009, possibly the same individual, in the same pond. No one was feeding fish when we approached, and the bird was positioned atop a nearby tree. After 15 min a small group of people began feeding fish at the pond's edge. The heron immediately flew from the tree and waded into the water next to the bread. The bird did not touch the bread, but caught a fish within 1 min. These observations are the first evidence of passive bait-fishing in Black-crowned Night Herons.

We observed up to four different Black-crowned Night Herons in February 2009 bait-fishing on five occasions in the Hamakua Marsh in the town of Kailua on the windward side of Oahu, Hawaii. The northeast side of the marsh is bordered by the Hamakua Canal, a narrow waterway between the marsh and a series of parking lots. Passers-by frequently feed birds and fish at the edge of one parking lot. On the first occasion, bread was distributed on a small patch of grass at the top of a 1 m bank. A mixed group of birds, including Common Pigeons (Columba livia), Red-crested Cardinals (Paroaria coronata), Mallards (Anas platyrhynchos), Hawaiian Moorhens (Gallinula chloropus sandvicensis), and a Black-crowned Night Heron quickly approached the bread. The Black-crowned Night Heron took a piece of bread in its bill and descended the bank to the edge of the canal. The heron placed the bread in the water and then stabbed at it repeatedly breaking it into smaller pieces. Within 20 sec the bird caught a fish. The heron then ascended the bank, retrieved another piece of bread and repeated the bait-fishing sequence. The heron caught four fish within 15 min. We also observed the heron place bread in the water and then reposition the bait when it began to float away.

On another occasion at the same location, we witnessed four different herons approach people feeding birds. Because the herons gathered so quickly, we concluded these birds regularly fished with bait at this location and could connect the presence of people with fish bait. The four individuals maintained at least a 3-m gap between each other while feeding, through the use of aggressive calls and chasing of competitors. The birds used a great deal of aggression when encountering other Black-crowned Night Herons within close range either at the water's edge or at the top of the bank where passers-by distributed bread. The four herons varied greatly in their bait-fishing abilities. One individual was very adept at gathering bread and manipulating the bread in the water (breaking bread into pieces and altering its position). Another bird also gathered bread and placed it in the water, but rarely repositioned the bait and was not seen to break bait into pieces. The other two Black-crowned Night Herons present did not actively use bait. Although bread was tossed directly at the feet of both birds, neither individual ever touched the bread. However, all four birds were successful in attempts at passive bait-fishing. When bread was thrown into the water within 1-2 m of any of the four herons, they lunged towards the bait to catch fish that rapidly gathered to eat the bread. Each of the four individuals caught multiple fish either with passive or active bait-fishing techniques.

DISCUSSION

Bait-fishing is one of the few examples of tool use by birds, but appears to be widespread among ardeids with seven different species catching fish with bait. Prior to our observations, researchers had reported only two observations (of 1 adult each) of Black-crowned Night Herons actively fishing with bread (in an urban park in California, McCullough and Beasley 1996; and in a park in New Orleans, Louisiana, Riehl 2001). Our observations are the first reports of passive bait-fishing in Black-crowned Night Herons. In addition, our observations of variable levels of passive and active bait-fishing in the same species support Lovell's (1958) suggestion that passive bait-fishing is a precursor to more active bait-fishing techniques.

Received 19 March 2009. Accepted 9 July 2009.

LITERATURE CITED

CROUS, R. 1994. An incidence of bait fishing in the Squacco Heron Ardeola ralloides. Babbler 26/27: 32.

HIGUCHI, H. 1986. Bait-fishing by the Green Heron Ardeola striata in Japan. Ibis 128:285-290.

HUNTER, M. L., A. CALHOUN, AND D. S. WILCOVE. 2004. Goliath Heron fishing with an artificial bait? Water-birds 27:312-313.

KEENAN, W. J. 1981. Green Heron fishing with mayflies. Chat 45:41.

LOVELL, H. B. 1958. Baiting of fish by a Green Heron. Wilson Bulletin 70:280-281.

MCCULLOUGH, D. D. AND R. J. BEASLEY. 1996. Bait-fishing herons. Bird Watcher's Digest 18:48-51.

NORRIS, D. 1975. Green Heron (Butorides virescens) uses feather lure for fishing. American Birds 29:652-654.

RIEHL, C. 2001. Black-crowned Night Heron fishes with bait. Waterbirds 24:285-286.

ZICKEFOOSE, J. AND W. E. DAVIS. 1998. Great Blue Heron (Ardea herodias) uses bread as bait for fish source. Colonial Waterbirds 21:87-88.

Michael C. Gavin (1,3) and Jennifer N. Solomon (2)

(1) School of Geography, Environment, and Earth Sciences, Victoria University of Wellington, P. O. Box 600, Wellington, New Zealand.

(2) 117 North Kalaheo Avenue, Kailua, HI 96734, USA.

(3) Corresponding author; e-mail: michael.gavin@vuw.ac.nz
Gale Copyright: Copyright 2009 Gale, Cengage Learning. All rights reserved.