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Anting behavior by the northwestern crow (Corvus caurinus) and American crow (Corvus brachyrhynchos).

Anting is one of the more peculiar behaviors performed by birds, and is widespread among Passeriformes. During this activity, birds deliberately introduce ants (Hymenoptera: Formicidae) into the plumage (Stresemann 1935; Simmons 1957; Potter 1970; Craig 1999). Anting occurs in 2 main forms: (1) active anting, where a bird preens its plumage with live ants grasped in the bill; and (2) passive anting, where a bird settles on an aggregation of ants and allows the ants to crawl through the plumage. Anting is an anointing activity used by many birds to apply scent-laden materials, usually chemicals of arthropods, to themselves (Weldon and Carroll 2007), and considered a maintenance behavior whose function is to either cleanse plumage of ectoparasites and accumulated lipids or to relieve skin irritation during feather replacement (Potter and Hauser 1974; Simmons 1986). Ehrlich and others (1986) proposed that anting serves to suppress feather and skin bacteria and fungi, although there is no evidence to support this (Potter 1989; Revis and Waller 2004). Other suggested functions of anting include self-stimulation (Whitaker 1957; but see Simmons 1966) and food preparation (Eisner and Aneshansley 2008; but see Querengasser 1973; Goodwin 1976). There is also the possibility that anting serves more than one purpose whose expression depends on the individual bird and context of the anting activity.

Anting remains a topic of contention and interest despite comprehensive literature reviews (for example Simmons 1957; Whitaker 1957; Chisholm 1959; Potter 1970; Potter and Hauser 1974; Craig 1999) and experimental studies of anting with captive birds (for example Querengasser 1973; Eisner and Aneshansley 2008). Thus, continued documentation of anting episodes by wild birds can contribute to the resolution of its function(s). Here we describe cases of anting by wild Northwestern Crows (Corvus caurinus) and a wild American Crow (Corvus brachyrhynchos), species for which anting by wild individuals has been infrequently reported. We also describe the context of the anting behavior. We further provide a brief review of anting behavior by North American Corvus and discuss common patterns.

On 31 August 1997, GN watched 25-30 Northwestern Crows at 11:30 PDT as they settled in the lawn at her house near Gooseberry Point opposite Lummi Island, Whatcom County, Washington (48[degrees]44'N, 122[degrees]41'W). Air temperature at the time was 24.5 [degrees]C, with clear sky and no wind. Most crows walked about on the lawn and frequently pecked in the grass, presumably feeding on winged and wingless ants that were swarming during a 2-d period; the ant species was not identified. At various times after landing on the lawn, 7 to 8 crows paused while pecking at the lawn, settled in the grass (in both green and dry patches), and pressed their partially spread wings, tails, and ruffled belly plumage to the ground, apparently anting. Anting individuals remained in one spot for up to 30 s then stood and moved to new locations where they assumed the anting posture and repeated the behavior. Some crows not anting approached anting individuals, whereupon the anting bird often vocalized, moved to another location on the lawn, and settled again on the grass in an anting posture. All anting behavior occurred in a period of 5 min during 15-20 min of observation. Anting and non-anting crows were in various stages of molting remiges and rectrices at the time of the observations.

On 15 August 2014, at 16:25 MDT, PH noticed an American Crow about 30 m distant that was anting among a group of 5 crows on a grassy athletic practice field on the edge of the University of Montana campus in Missoula, Montana (46[degrees]52'N, 113[degrees]59'W). The anting crow had its breast pressed to the grass, the back, head, and neck plumage slightly ruffled with wings half unfolded at its sides, the wings and partially spread tail also pressed to the grass. The sky had been overcast throughout the day, during which it rained in the morning and began to rain about 15 min after the observations ended; air temperature at the time was 24[degrees]C. The anting crow poked at the grass with its bill a few times as it squatted, stood and walked about 1 m, then settled again in the grass in the posture described above. It remained settled about 30 s and poked again in the grass a few times. The other 4 crows, about 10-25 m distant, neither anted nor showed any interest in the anting individual. Again, after about 30 s the anting crow stood and moved about 1 m to a 3rd location, assumed the anting posture, and repeated the behavior previously described. Altogether, the focal crow anted for about 3 min within a linear distance of 3 m before flushing upon the approach of PH to about 20 m, whereupon it flew to the other crows foraging nearby and joined them in foraging without displaying additional anting or plumage maintenance behavior. While in flight it was evident that the anting crow was in the process of molting remiges. The grass where the bird anted was 6 cm deep. Upon parting the grass in the area where the crow anted and probed with its bill, PH found a colony of winged and wingless dark amber-colored ants [less than or equal to] 3 mm in body length that were swarming on dirt piled among the base of the grass and on the grass itself. PH was unable to preserve any of the ants, which remained unidentified. Because of their small size and lawn habitat, however, they were likely not a species of Camponotus or Formica, 2 genera frequently used for anting by other bird species (Whitaker 1957; Potter 1970), with Formica reported during anting activity by North American Corvus (Weber 1935; Hendricks 1980; Wiles and McAllister 2011).

The new observations we report here of anting behavior by American and Northwestern Crows fit descriptions of passive anting (Simmons 1957, 1966), where birds settle on concentrations of ants and allow them to invade the plumage. Sometimes passively anting birds appear to actively "stir up" the ants by frequent repositioning of the body, wings, and tail, and poking at ants on the ground with their bills. We saw all of these behaviors performed by the crows we observed, and they appear to provoke ants and intensify their swarming; when PH parted the lawn with his fingers where the American Crow had been anting, the ants began to swarm up the grass blades onto his fingers.

Anting is prevalent among the Corvidae, particularly the genus Corvus. Species for which there are reports of anting include Rook (C. frugilegus), Carrion Crow (C. corone), Hooded Crow (C. cornix), and Common Raven (C. corax) in Europe (Simmons 1957; Goodwin 1976), Australian Raven (C. coronoides) in Australia (Chisholm 1959), and Hawaiian Crow (C. hawaiiensis) in the Hawaiian Islands of the Pacific Ocean (Banko and others 2002). Only active anting has been reported for Common and Australian Ravens; only passive anting for Hooded and Hawaiian Crows.

Anting has apparently been reported only for Northwestern Crow and American Crow among North American Corvus whose ranges extend north of Mexico (Verbeek and Butler 1999; Verbeek and Caffrey 2002); we found no reports of anting for Common Raven, Chihuahuan Raven (C. cryptoleucus), and Fish Crow (C. ossifragus) (see for example Boarman and Heinrich 1999; McGowan 2001; Bednarz and Raitt 2002). Accounts of anting pertain to wild as well as tame or captive crows (Table 1) many of which, unfortunately, lack sufficient detail to determine the full context of the behavior. Passive anting has been reported in all published accounts of the behavior by North American Corvus; active anting is reported only for American Crow (Kilham 1989). Some of Kilham's (1989) observations of active anting may actually be of birds picking at and removing ants in the plumage, as he did not note vigorous preening with ants, which is typical for active anting (Whitaker 1957; Potter 1970; Potter and Hauser 1974). Passive anting is very similar in appearance to sunning (Potter and Hauser 1974; Simmons 1986; PH, pers. obs.), so some reports of anting could actually be of birds sunning. Associating the presence of ants with bouts of passive anting should assure the distinction between the 2 behaviors. All of the reports in Table 1 note that ants were present where anting was observed, with the exception of the September record of Kilham (1989) which, however, occurred on a day with morning rain and may have been overcast, thereby making sunning behavior unlikely.

Food preparation (for example Eisner and Aneshansley 2008) does not seem to provide an explanation for most observations of passive anting, including the ones we describe here, because the birds engaged let ants freely wander unmolested through the plumage and rarely appear to be eating them (Whitaker 1957). A more logical explanation for passive anting is that it is somehow related to plumage maintenance. The crows we observed anting were in various stages of molt, supporting the hypothesis that anting activity is performed during widespread feather replacement to soothe irritated skin through the application of formic acid produced by ants (Potter 1970; Potter and Hauser 1974). Widespread growth of new feathers often occurs during periods of high humidity when anting is also commonly observed (Potter and Hauser 1974), and our observations are consistent with this. Timing of other observations (Table 1), however, suggests that soothing irritated skin may not be the only reason for passive anting, as Potter (1970) also acknowledged.

Key words: American Crow, anting, behavior, Corvus brachyrhynchos, Corvus caurinus, Montana, Northwestern Crow, Washington

Acknowledgments.--The senior author is very grateful to the late Reverend G Norment for sharing her observation of anting behavior by Northwestern Crows. Our paper was improved by thoughtful comments from C Cestari and PJ Weldon.

Literature Cited

Banko PC, Ball DL, Banko WE. 2002. Hawaiian Crow (Corvus hawaiiensis). In: Poole A, Gill F, editors. The birds of North America, No. 648. Philadelphia, PA: The Birds of North America, Inc.

Bednarz JC, Raitt RJ. 2002. Chihuahuan Raven (Corvus cryptoleucus). In: Poole A, Gill F, editors. The birds of North America, No. 606. Philadelphia, PA: The Birds of North America, Inc.

Boarman WI, Heinrich B. 1999. Common Raven (Corvus corax). In: Poole A, Gill F, editors. The birds of North America, No. 476. Philadelphia, PA: The Birds of North America, Inc.

Chisholm AH. 1959. The history of anting. Emu 59: 101-130.

Craig AJFK. 1999. Anting in Afrotropical birds: A review. Ostrich 70:203-207.

Ehrlich PR, Dobkin DS, Wheye d. 1986. The adaptive significance of anting. Auk 103:835.

Eisner T, Aneshansley D. 2008. "Anting" in Blue Jays: Evidence in support of a food-preparatory function. Chemoecology 18:197-203.

Frazar AM. 1876. Intelligence of a crow. Bulletin of the Nuttall Ornithological Club 1:76.

Goodwin D. 1976. Crows of the world. Ithaca, NY; Cornell University Press. 354 p.

Heinrich B. 1987. One man's owl. Princeton, NJ: Princeton University Press. 224 p.

Hendricks P. 1980. Anting by Common Crows. Journal of Field Ornithology 51:177-178.

Ivor HR. 1956. The enigma of bird anting. National Geographic 110:105-119.

Kilham L. 1989. The American Crow and the Common Raven. College Station, TX: Texas A & M University Press. 255 p.

McGowan KJ. 2001. Fish Crow (Corvus ossifragus). In: Poole A, Gill F, editors. The birds of North America, No. 589. Philadelphia, PA: The Birds of North America, Inc.

Potter EF. 1970. Anting in wild birds, its frequency and probable purpose. Auk 87:692-713.

Potter EF. 1989. Response to P.R. Ehrlich, D.S. Dobkin, and D. Wheye. Auk 106:163-164.

Potter EF, Hauser DC.1974. Relationship of anting and sunbathing to molting in wild birds. Auk 91: 537-563.

Querengasser A. 1973. Uber das Einemsen von Singvogeln und die Reifung dieses Verhaltens. Journal fur Omithologie 114:96-117.

Revis HC, Waller DA. 2004. Bactericidal and fungicidal activity of ant chemicals on feather parasites: An evaluation of anting behavior as a method of self-medication in songbirds. Auk 121: 1262-1268.

Simmons Kel. 1957. A review of the anting-behaviour of passerine birds. British Birds 10:401-424.

Simmons Kel. 1966. Anting and the problem of self-stimulation. Journal of Zoology 149:145-162.

Simmons Kel. 1986. The sunning behaviour of birds. Bristol, UK: Bristol Ornithological Club. 119 p.

Stresemann E. 1935. Die Beniitzung von Ameisen zur Gefiederpflege. Omithologische Monatsberichte 43:134-138.

Verbeek NAM, Butler RW. 1999. Northwestern Crow (Corvus caurinus). In: Poole A, Gill F, editors. The birds of North America, No. 407. Philadelphia, PA: The Birds of North America, Inc.

Verbeek NAM, Caffrey C. 2002. American Crow (Corvus brachyrhynchos). In: Poole A, Gill F, editors. The birds of North America, No. 647. Philadelphia, PA: The Birds of North America, Inc.

Weber NA. 1935. The biology of the thatching ant, Formica rufa obscuripes Forel, in North Dakota. Ecological Monographs 5:165-206.

Weldon PJ, Carroll JF. 2007. Vertebrate chemical defense: Secreted and topically acquired deterrents of arthropods. In: Debboun M, Frances SP, Strickman D, editors. Insect repellents: Principles, methods, and uses. Boca Raton, FL: CRC Press, p 47-74.

Whitaker LM. 1957. A resume of anting, with particular reference to a captive Orchard Oriole. Wilson Bulletin 69:195-262.

Wiles GJ, McAllister KR. 2011. Records of anting by birds in Washington and Oregon. Washington Birds 11:28-34.

Philip L Wright Zoological Museum, Division of Biological Sciences, University of Montana, 32 Campus Drive, Missoula, MT 59812 USA (PH),; 2524 Lummi View Drive, Bellingham, WA 98226 (GN). Submitted 29 December 2014, accepted 6 March 2015. Corresponding Editor: Joan Hagar.
TABLE 1. Published reports of anting by the Northwestern Crow
(Corvus caurinus) and American Crow (C. brachyrhynchos).

                    Month     Anting form     Wild bird   Molting

Northwestern Crow
                    ?       passive           no          ?
                    ?       passive           yes         ?
                    Aug     passive           yes         yes
American Crow
                    ?       passive           no          ?
                    ?       passive           yes         ?
                    May     passive           yes         yes?
                    May     passive, active   yes         ?
                    Jul     passive, active   no          ?
                    Aug     passive           yes         yes
                    Sep     passive, active   yes         ?

                    Month           Weather            Source (a)

Northwestern Crow
                    ?       ?                          8
                    ?       ?                          6
                    Aug     sunny, 24.5[degrees]C      10
American Crow
                    ?       ?                          1,2,4,7,8
                    ?       ?                          8,9
                    May     sunny, 18.5[degrees]C      3
                    May     sunny                      5
                    Jul     ?                          5
                    Aug     prior rain, 25[degrees]C   10
                    Sep     prior rain                 5

(a) (1) Frazar 1876; (2) Heinrich 1987; (3) Hendricks 1980; (4)
Ivor 1956; (5) Kilham 1989; (6) Verbeek and Butler 1999; (7) Weber
1935; (8) Whitaker 1957; (9) Wiles and McAllister 2011; (10) this
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Title Annotation:GENERAL NOTES
Author:Hendricks, Paul; Norment, Gwen
Publication:Northwestern Naturalist: A Journal of Vertebrate Biology
Article Type:Report
Date:Sep 22, 2015
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