--The adaptive value of a behavioral trait usually is assessed in terms of its costs and benefits. Although the ultimate units of interest are fitness units, proximate measures such as time and energy expenditure or risk incurred by the performer usually are used as fitness surrogates, for expediency. Time and energy expenditures are more readily quantified than risk and thus have tended to dominate discussions of the costs of behavior. In the case of antipredator behavior, however, time-energy investment may be a poorer approximation of cost than is risk (Trivers 1972). Even for species like the American Avocet (Recurvirostra americana), in whose breeding biology antipredator behavior seems to play a major role (Sordahl 1986), mobbing and distraction of predators consumes only a small part of the daily time budget (Gibson 1978). Risk, however, is an elusive factor. Predation is rarely observed, and injury or mortality resulting from mobbing or distraction of a predator is a very small subset of all natural predation events. Furthermore, because mobbing and distraction usually occur in a context of parental care (Shedd 1978, 1982; So rdahl 1986) and because parental care is essential for the survival of the eggs or young in virtually all birds, death or injury resulting from these behaviors is expected to be rare because parental self-sacrifice would be counter- selected (Skutch 1976, Gochfeld 1984). Most authors simply note that these behaviors appear to be risky but probably are not highly so because: (1) the performer is alert and aware of the predator, and (2) there is little contrary evidence. It is the purpose of this paper to show that the risks of mobbing and distraction, though they may be statistically small (Gochfeld 1984:353, Hennessy 1986), are not negligible (see also Curio and Regelmann 1986). I include a literature review of anecdotes describing negative outcomes for performers of these be- haviors. Review of literature.- Predators often seem reluctant to leave an area when mobbed (pers. obs.), creating a situation with potential for aggression toward vigorous mobbers. Predators have often been reported to attack their mobbers (Forbush and May 1939:102; Meiner- tzhagen 1959:98, 162; Cade 1962:398; Cade 1967:49; Stefanski and Falls 1972:1509; B6ck- ing pers. comm. in Curio 1978:178). There are many other reports of mobbers being killed or captured by the predator (Mason 1915; Forbush 1927:109; MacIntyre 1936 in Watson 1977:89; Broun 1947; Meinertzhagen 1959:87, 88, 119, 162; Cade 1962:395; Wetmore 1965:439; Friemann 1975; Myers 1978; Denson 1979; Todd 1980; McCafiery 1982; Walker 1983; England 1986; Wilson 1986). Predators such as large falcons that prey on adult birds may be particularly dangerous to mob. Meinertzhagen (1959:162) noted that the Northern Hobby (Falco subbuteo) is intolerant of mobbing, and Burger (pers. comm. in Gochfeld 1984:354) saw a Peregrine Falcon (F. peregrinus) capture one of the Common Terns (Sterna hirundo) that was mobbing it over a colony. Gochfeld (1984:354) further noted that he has captured mobbing Common Terns by hand. Some predators may actually capitalize on mobbing by hunting in pairs or provoking mobbing as a hunting strategy (Smith 1969). Mobbing may be so intense that the mobber fails to see a second predator (Rudebeck 1950- 51:208). Southern (1970) repeatedly observed a Northern Harrier (Circus cyaneus) chasing crows in a group that was mobbing a Great Horned Owl (Bubo virginianus), suggesting that it was trying to take advantage of their preoccupation. Distraction behavior is probably less dangerous than mobbing, because it usually is per- formed at a somewhat greater distance from the predator. I found only two records of a distracting bird being killed by the predator to which it was displaying (Jourdain 1936:32, Brunton 1986). But Balda's (1965) observation of a Loggerhead Shrike (Lanius ludovicianus) killing a Mourning Dove (Zenaida macroura) that was distracting the author illustrates a dangerous property of distraction behavior--it attracts more predators than initially were 350 THE WILSON BULLETIN ß Vol. 102, No. 2, June 1990 present. The circumstances of distraction display may also create significant psycho-phys- iological stress, even resulting in the displayer's death (Graul 1975:16, Blohm 1981). Discussion.--The 35 examples cited above of birds being attacked, captured, killed, or dying of stress while mobbing (N = 30) or distracting (N = 5) a predator document that these behaviors are dangerous. As Hennessy (1986) pointed out, their level of danger (i.e., the probability of injury or death for an individual) relative to other behaviors is not known. Such data would be extremely ditficult to obtain. However, there are other reasons to believe that mobbing and distraction are highly risky (Curio and Regelmann 1986), such as geo- graphical variation in mobbing that is appropriate to the danger posed by local predators (curio 1975). From a theoretical viewpoint, because the ability of many bird species to harm a predator is questionable, it may be necessary for mobbets to endanger themselves in order to "convince" the predator that their threat is real (Zahavi 1977). The threat, then, may be a sort of challenge which should often be declined because of the dissimilar benefits and costs for mobbet and predator (Maynard Smith and Parker 1976, Dawkins and Krebs 1979). The vulnerability of a mobbing or distracting bird should correlate with the distance from the predator at which the display is performed. Proximity increases the displayer's con- spicuousness and the probability of eliciting an attack. An important corollary is that the effectiveness of display is probably related directly to the risk involved. It is noteworthy that distraction display practically is nonexistent in groups other than birds (Armstrong 1954:128), presumably because the risks are too high if the decoy cannot escape into an element out of the predator's reach. Even terrestrial predators such as dogs often come quite close to capturing displaying shorebirds and ducks (pets. obs.). Instances of birds distracting their avian predators are rare (Armstrong 1954:127, pets. obs.). Thus ground predators, particularly mammals, are the chief recipients of distraction behavior. In summary, birds that mob or distract predators place themselves in close proximity to dangerous animals that may attack them. No quantitative risk assessments for individual birds have yet been made. However, I cite here 35 reports from the literature of birds being attacked or dying while mobbing or distracting a predator. Taken together, these anecdotes strongly support the hypothesis that mobbing and distracting birds are at deadly risk. Acknowledgments.--I thank K. L. Dixon, M. Gochfeld, C. R. Blem, and an anonymous reviewer for suggestions that have improved the manuscript. The many people who have asked me if the apparent risks of mobbing and distraction are real stimulated me to write it. Assistance with references was provided by the Wilson Ornithological Society's Van Tyne Memorial Library at the University of Michigan Museum of Zoology. LITERATURE CITED AgMSTgONG, E.A. 1954. The ecology of distraction display. Br. J. Anim. Behar. 11:121- 135. B^LD^, R.P. 1965. Loggerhead Shrike kills Mourning Dove. Condor 67:359. BLOHM, R. J. 1981. Incubating female Gadwall dies upon flushing from nest. J. Field Ornithol. 52:149-150. Bgou, M. 1947. Golden Eagle captures Red-shouldered Hawk. Auk 64:317-318. BgtrNTON, D.H. 1986. Fatal antipredator behavior of a Killdeer. Wilson Bull. 98:605- 607. CADœ, T.J. 1962. 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