William E. Davis, Jr.
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Fig. 1. The Anhinga pounds the captured fish against a branch. All photos by the author
On January 31, 2019, during a visit to Everglades National Park, I witnessed an attempted kleptoparasitism of an adult male Anhinga (Anhinga anhinga) by two Purple Gallinules (Porphyrio martinica). I was on Anhinga Trail watching an Anhinga swimming among the lily pads when I saw it catch a sunfish-shaped fish about eight inches long. Carrying the fish, the Anhinga climbed out of the water onto a branch of an emergent shrub (Figure 1) where it proceeded to bash the fish against the branch. After several minutes, a Purple Gallinule approached by walking across the lily pads (Figure 2). The gallinule then swam over to just below the Anhinga, flapped out of the water, and lunged at the fish with its bill, attempting to grab the fish from the Anhinga. The Anhinga held firm, thwarting the attempt. The gallinule remained in the area when, several minutes later, a second Purple Gallinule arrived and hopped up onto the branch facing the Anhinga. This second gallinule then lunged at the Anhinga and attempted to grab the fish with its beak. The Anhinga pulled the fish away and for a moment the two birds were in contact with wings flapping. The Anhinga then dropped the fish into the water and dove to retrieve it, and the gallinules departed, ending the episode. This sequence appears to be an example of an attempt at interspecific kleptoparasitism (food stealing).
Interspecific kleptoparasitism is found in many families of birds including the shorebirds (Davis and Jackson 2007, Davis 2016), is common in other groups such as the gulls (Laridae), and is essentially a way of life in some such as jaegers (Laridae) and frigatebirds (Fregatidae). I found no reports of interspecific kleptoparasitism in the Birds of North America (BNA) accounts of the Purple Gallinule (West and Hess 2002) or closely related Common Gallinule (Gallinula galeata) (Bannor and Kiviat 2002). However, there is a reference in the BNA account of the American Coot (Fulica Americana) to Coot's interspecific kleptoparasitism of waterfowl among which they feed (Brisbin and Mowbray 2002).
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Fig. 2. The Anhinga is approached by the first of two Purple Gallinules.
The question is: why would the Purple Gallinules attempt to steal a fish from an Anhinga? The answer may lie in the foraging habits and general temperament of Purple Gallinules. The species forages primarily on vegetation, especially the flowers, seeds, and fruits of aquatic plants. However, they do take animal material such as arthropods, annelids, mollusks, and small fish that may constitute more than half of their dietary intake in spring and summer (West and Hess 2002). They are often highly kleptoparasitic within their own species, especially within family groups. One such instance was reported where the young and adults of a family of Purple Gallinules chased and squabbled over frogs that had been caught, pulling the frogs to pieces in the process as all family members struggled to obtain a piece. Also included in the BNA account were instances of Purple Gallinules taking Wood Duck (Aix sponsa), Snowy Egret (Egretta thula), and Common Grackle (Quiscalus quiscula) chicks, and an Anhinga egg. A Purple Gallinule carrying a heron chick had to fly to avoid being kleptoparasitized by another Purple Gallinule. Purple Gallinules are highly territorial during breeding season, with parents and juveniles participating in territorial defense. Actual fighting is common in some populations where in one instance approximately two-thirds of territorial disputes involved actual fighting. Purple Gallinules are clearly aggressive birds, and it seems likely that the attempted kleptoparasitism of an Anhinga's fish as reported here was an attempt to acquire food.
Literature cited
- Bannor, B. K., and E. Kiviot. 2002. Common Gallinule (Gallinula galeata), version 2.0. In The Birds of North America (A. F. Poole and F. B. Gill, eds.). Ithaca, New York: Cornell Lab of Ornithology.
- Brisbin, I. L., Jr., and T. B. Mowbray. 2002. American Coot (Fulica Americana), version 2.0. In The Birds of North America (A. F. Poole and F. B. Gill, eds.). Ithaca, New York: Cornell Lab of Ornithology.
- Davis, W. E., Jr. 2016. Shorebird behavior on their wintering grounds. Bird Observer 44: 266–269.
- Davis, W. E., Jr., and J. A. Jackson. 2007. Willets kleptoparasitize and use White Ibises as "beaters." Wilson Journal of Ornithology 119: 758–760.
- West, R. L., and G. K. Hess. 2002. Purple Gallinule (Porphyrio martinica), version 2.0. In The Birds of North America (A. F. Poole and F. B. Gill, eds.). Ithaca, New York: Cornell Lab of Ornithology.
William E. Davis, Jr.