374 Southeastern Naturalist Vol. 10, No. 2 Rapid Change in the Defense of Flightless Young by a Mourning Dove Parent James B. Berdeen1,2,* and David L. Otis3,4 Abstract - We report that an adult-sized Zenaida macroura (Mourning Dove), presumably a parent, rapidly decreased risk taken in defense of a juvenile as the likelihood of predation to the juvenile increased. We attribute this decrease in risk taken to (1) the parent’s perception that the risk of predation had increased to the extent that a continuation of defensive behaviors would not prevent the death of the juvenile, and (2) its attempt to minimize its own risk of death. It may be that there is a threshold beyond which Mourning Dove parents will forgo the risk of additional defense of offspring in favor of making another reproductive attempt. Introduction The reproductive ecology of Zenaida macroura L. (Mourning Dove) has been well studied (Sayre and Silvy 1993), but there has been relatively little investigation of this species’ defense of young against potential predators. However, there is documentation of adult Mourning Doves performing distraction displays when their eggs or young are approached by humans (Hanson and Kosack 1963, Nice 1923, Sayre et al. 1993). This behavior has been referred to as a nest-distraction display (Sayre et al. 1993). Three variations of distraction displays were described by Nice (1923). Adult Mourning Doves may (1) “throw themselves on the ground near the intruder and flutter about as if seriously injured”; (2) fly a short distance (less than 30 m), land and flutter their wings, wave their wings while stopped, walk and continue waving their wings, make brief flights, land, and repeat the process; or (3) “fly near the ground as if it is intending to make a demonstration”, then fly and land in a tree (Nice 1923:37–38). Additionally, Westmoreland (1989:1063) classified variations (1) and (2) as “high-intensity” displays and (3) as a “low-intensity” display, and considered a parent remaining on the nest for a substantial period of time as a potential predator approached to be relatively risky. The incidence and intensity of Mourning Doves’ distraction displays are somewhat variable. Some parents do not perform these displays when their nests are approached by humans, but others engage in these behaviors “throughout the nesting cycle” (Nice 1923:40–41). It is common for some parents to perform a high-intensity display when a researcher visits its nest, but then perform a lowintensity display during a subsequent visit (Westmoreland 1989). Multiple influences contribute to this variability. Age of offspring is positively associated with both the incidence (Nice 1923) and intensity (Westmoreland 1Department of Aquaculture, Fisheries, and Wildlife, G-08 Lehotsky Hall, Clemson University, Clemson, SC 29634. 2Current address - Minnesota Department of Natural Resources, Wetland Wildlife Populations and Research Group, 102 23rd Street NE, Bemidji, MN 56601. 3United States Geological Survey, South Carolina Cooperative Fish and Wildlife Research Unit, Clemson University, Clemson, SC 29634. 4Current address - Iowa Cooperative Fish and Wildlife Research Unit, Department of Animal Ecology, Iowa State University, Ames, IA 50011. *Corresponding author – james.berdeen@gmail.com. 374 Notes of the Southeastern Nat u ral ist, Issue 10/2, 2010 2011 Southeastern Naturalist Notes 375 1989) of distraction displays. Given that a parent is more likely to perform a distraction display if its mate also engages in this behavior (Nice 1923), it appears that social influences affect incidence of displays. We report an observation of behaviors performed by an adult-sized Mourning Dove in defense of a flightless juvenile, and describe the change in behavior of the adult-sized bird as its risk of mortality changed. We compare these behaviors with those previously documented, and provide explanations for this behavioral change. Observation. On 23 July 1999 at approximately 0830 EST, two field personnel were driving on an unimproved forest road at the Cuddo Unit of Santee National Wildlife Refuge (NWR; 33°31'N, 80°17'W) in the Coastal Plain of South Carolina. The habitat immediately adjacent to this road was mature, mixed Pinus taeda L. (Loblolly Pine)-deciduous forest with a well-developed understory. A cornfield adjacent to this stand was approximately 30 m from the roadbed. We observed an adult-sized Mourning Dove fly weakly from the roadbed when our vehicle approached to within approximately 2 m. The bird flew at approximately 0.3 m altitude and <10 m distance, and landed on a perch in the forest understory. This behavior appeared to be a distraction display similar to variation 3 of Nice (1923). We observed a flightless juvenile Mourning Dove on the ground <1 m from where the adult-sized dove flushed. We assume that adult-sized bird was the parent of the juvenile because it is unlikely that an adult Mourning Dove would defend any juvenile other than its own, and hereafter refer to the former as the parent. The juvenile was captured, marked with a standard US Geological Survey (USGS) leg band, and weighed with a Pesola scale. It appeared to be 8–9 days old based on the photographs and written description of Mirarchi (1993), but its weight (59 g) was closer to that of an 11–12 day-old juvenile (Holcomb and Jaeger 1978). Because Mourning Doves typically fledge at 13–15 days-old (Otis et al. 2008), this juvenile probably left the nest prematurely, perhaps during the wind and thunderstorms that occurred during the previous evening (see Morrow and Silvy 1982, Sayre and Silvy 1993). We did not locate the nest after a brief search from the ground. During banding of the juvenile, the parent flew from its understory perch to an altitude just above the overstory and circled the vicinity three times. The parent then flew through the woods and away from the area, which we infer was the termination of the distraction display. We were in visual contact with the parent for <2 min. After banding, we placed the juvenile on an understory perch approximately 1 m above ground level and left the vicinity. Personnel returned twice later that day, and observed a juvenile at the same perch at approximately 1000 EST but not at 1600 EST. We do not know if the parent returned to the juvenile after field personnel left the area. No re-encounters of this juvenile were reported to the USGS Bird Banding Lab as of December 2009; thus its fate is unknown. Discussion. Two facets of our observation are similar to previously described behaviors. First, parents will remain close to their offspring and perform a 376 Southeastern Naturalist Vol. 10, No. 2 distraction display when young on the ground (presumably fledglings) are approached by humans (Nice 1923), which Mourning Doves probably perceive as potential predators. Second, the parent’s weak flight away from the flightless juvenile and subsequent landing in the nearby understory is similar to variation 3 of Nice (1923). There is no documentation of an adult Mourning Dove’s rapid decrease in the risk taken in the defense of a juvenile in scientific literature, but such a phenomenon has been observed by other researchers (D. Westmoreland, US Air Force Academy, Colorado Springs, CO, pers. comm.). It appears that the parent initially engaged in the relatively risky behavior of remaining near the flightless juvenile when potential predators approached their location, then performed a low-intensity distraction display when the potential predators had moved to ≤2 m from the juvenile, and finally appeared to terminate its display when the potential predator captured the juvenile. There are two explanations for this decrease in defense. First, the parent may have perceived that the risk of predation had increased to the extent that a continuation of protective behaviors would not prevent the death of the juvenile. This explanation is consistent with the idea that life-history traits should evolve based not on prior investment but anticipated benefits (Dawkins and Carlisle 1976, Robertson and Biermann 1979). Second, the parent may have altered its behavior to minimize its own risk of death. It may be that there is a threshold beyond which Mourning Dove parents will forgo the risk of additional defense of offspring in favor of making another reproductive attempt. This explanation is consistent with the reproductive strategy of the Mourning Dove; i.e., maximizing fitness by producing multiple clutches during a single breeding season and expending limited parental investment on a single clutch (see Westmoreland et al. 1986). Both explanations require the assumptions that Mourning Dove parents can quickly perceive a change in the risk of mortality and respond in a manner that increases fitness. These explanations are not mutually exclusive if parents can almost simultaneously assess the risk of mortality to both themselves and their offspring. Distraction displays likely function to reduce the proportion of offspring killed by predators. However, Mourning Dove parents perform these displays somewhat inconsistently (Nice 1923), and this behavioral variability is only partially explained by the age of offspring and behaviors of a mate (Westmoreland 1989). It may be that some of the unexplained variation is attributable to changes in parents’ perception of risk of mortality during encounters with potential predators. Acknowledgments. Funding for this project was provided by the US Fish and Wildlife Service Webless Migratory Upland Game Bird Research Fund, USGS - Biological Resources Division South Carolina Cooperative Fish and Wildlife Research Unit, South Carolina Department of Natural Resources, South Carolina Public Service Authority (Santee Cooper), Clemson University, and Safari Club International. Logistical support was provided by Santee NWR personnel. We thank K. Sughrue for her assistance with this phase of the research project. D. Rave and K. 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