Northeastern Naturalist Vol. 26, No. 2 S.K. Peltier, C.M. Wilson, and R.D. Godard 2019 251 2019 NORTHEASTERN NATURALIST 26(2):251–260 Wing-flashing by Northern Mockingbirds While Foraging and in Response to a Predator Model Sarah K. Peltier1,2, C. Morgan Wilson1,*, and Renee D. Godard1 Abstract - Some insectivorous avian species may improve foraging success by flashing conspicuously colored wing patches or tail spots to startle potential prey and elicit escape behavior. While some studies of Mimus polyglottos (Northern Mockingbird) suggest that wing-flashing (WF) behavior may enhance strike rate and/or foraging success, other studies are equivocal or suggest a negative relationship. Anecdotal observations suggest that WF in mockingbirds may serve an additional role, as this behavior has been documented in response to a potential predator. The biological roles of WF remain unclear in Northern Mockingbirds; thus, we sought to systematically study: (1) the seasonal use of WF while foraging, and (2) the behavioral response of mockingbirds when presented with 2 model organisms—a nest predator and a neutral avian species. We found that foraging bouts during the reproductive period were more likely to include WF than those during the nonreproductive period, but that there was no significant relationship between WF rate and either strike rate or foraging-success rate. When exposed to models, mockingbirds only employed WF during the reproductive period, and then, only to the predator model. Our results suggest that WF is confined primarily to the reproductive period of the annual cycle, and that this behavior is utilized while foraging and in response to the presence of a potential predator. However, the biological role WF plays in both of these circumstances bears further examination. Introduction Some insectivorous avian species flash conspicuous plumage patches on wings, rumps, and/or tails while foraging, enhancing foraging efficiency by flushing potential insect prey so that they can be pursued and captured (i.e., the flush–pursue foraging mode; Remsen and Robinson 1990). This exposure of contrasting plumage patterns and exaggerated movements may stimulate insect neural pathways that elicit escape behavior (Galatowitsch and Mumme 2004, Jablonski and Strausfeld 2000, Jablonski et al. 2006) and thus, may facilitate prey capture by avian predators. Studies of Myioborus pictus (Swainson) (Painted Redstart) and Myioborus miniatus (Swainson) (Slate-throated Redstart) show that birds that flash white patches on their wings and tails engage in more chases of insect prey than do birds that do not flash (Jablonski 1999), and that birds with artificially darkened patches are involved in fewer chases (Jablonski 1999, Mumme 2002) and feed offspring at lower rates (Mumme 2002). Similarly, when the white tail-spots of Setophaga citrina (Boddaert) (Hooded Warbler) were experimentally darkened, both males 1Department of Biology, Hollins University, Roanoke, VA 24020. 2Florida Fish and Wildlife Conservation Commission, Naples, FL 34114. *Corresponding author - mwilson@hollins.edu. Manuscript Editor: Susan Smith Pagano Northeastern Naturalist 252 S.K. Peltier, C.M. Wilson, and R.D. Godard 2019 Vol. 26, No. 2 and females showed a reduction in the frequency of aerial-prey attack, and females delivered fewer winged insects and more insect larvae to nestlings (Mumme 2014). Mimus polyglottos L. (Northern Mockingbird) often wing-flashes (WF) to reveal white patches on primary feathers (Fig. 1, see Hailman 1960a for detailed description of behavior). While WF in mockingbirds has long been described in the literature, the specific function(s) of WF in this primarily ground-foraging species remains unclear. Gander (1931) first proposed the possible role WF may play in startling potential insect prey. Both Allen (1947) and Hailman (1960a) suggested that WF may increase foraging efficiency by stimulating an escape response in cryptic or sluggish insect prey. In support, Hailman (1960a) found that WF was strongly associated with foraging behaviors and that two-thirds of observed WFs were followed by prey strikes (2nd year of study). Further, Hailman provided anecdotal evidence that WF is rare in winter months when flying insect prey are uncommon (Hailman 1960b, see also Sutton 1946). In contrast, Hayslette (2003) observed that WF by Northern Mockingbirds occurred in only 30.5% of foraging bouts, and that there was a negative relationship between WF rate and foraging-strike rate. As such, he proposed that WF in Northern Mockingbirds may serve to stimulate quick escape responses in insect prey that are energetically expensive to pursue, thus allowing these birds to assess prey and focus on those that are more easily captured (Hayslette 2003). With this prey-assessment model of WF, Hayslette (2003) proposed that there should be a positive relationship between WF rate and success rate (rather than strike rate). Although most recent studies of WF have focused on its potential role in foraging, several studies have proposed that WF behavior in Northern Mockingbirds is also employed when confronting a novel object or in agonistic display to a potential predator. Given several observations of adult and fledgling mockingbirds displaying WF to inanimate objects, Sutton (1946) proposed that WF is an innate response indicating a bird’s suspicion or mistrust of something novel. Observations by Selander and Hunter (1960) indicated that mockingbirds readily WF to a taxidermied Otus asio L. (Screech Owl) placed on active territories. Further, observations by Dhondt and Kemink (2008) suggested that WF, alone or in conjunction with “hew” and “chatburst” vocalizations, occurs in direct response to the presence of Herpestes javanicus (É. Geoffroy Saint-Hilaire) (Mongoose) on a breeding territory where fledglings were present. Additional anecdotal reports of Northern Mockingbirds (Hicks 1955) and other mimids displaying WF to snake species support this idea (Michael 1970: Toxostoma rufum L. [Brown Thrasher], Dumetella carolinensis L. [Gray Catbird]; Burtt et al. 1994: Mimus macdonaldi [Ridgway] [Hood Mockingbird]). To better understand the role of WF, we systematically studied WF behavior in Northern Mockingbirds during natural foraging bouts. We predicted that WF would occur more often during the reproductive period (spring and summer) because Northern Mockingbirds face greater energetic demands (Dhondt and Kemink, 2008) and potentially responsive invertebrate prey are more abundant during this time of the annual cycle (Hailman 1960a, b). Further, we predicted that WF rate would be Northeastern Naturalist Vol. 26, No. 2 S.K. Peltier, C.M. Wilson, and R.D. Godard 2019 253 Figure 1. Wing-flashing Northern Mockingbirds open their wings in a series of distinct motions which flash the white wing-patches (as described in Hailman 1960a). The motion often ends in a near vertical position of the wings followed by a quick smooth return to the body. Pen and ink drawing by Kristin N. Bell. Northeastern Naturalist 254 S.K. Peltier, C.M. Wilson, and R.D. Godard 2019 Vol. 26, No. 2 positively related to ambient temperature, as invertebrate prey may be more active as temperatures increase. While foraging bouts can be readily observed, responses to predators are much more unpredictable and difficult to observe. As such, we examined the role of WF as a response to predators by observing the behavior of mockingbirds in response to a model of a known nest-predator and a neutral model placed in territories. We predicted that Northern Mockingbirds would be more likely to WF to the predator model and that this behavior would only occur during the reproductive season, when potentially vulnerable eggs and nestlings are present. Methods We conducted focal observations of foraging Northern Mockingbirds from June 2012 through March 2014 on the Hollins University (Roanoke, VA) campus and in residential yards, cemeteries, urban landscapes, and public parks in Roanoke, Botetourt, and Bedford counties, VA. All observations occurred between 1 h and 5 h after sunrise (mean ± SE = 3.23 ± 0.17 h after sunrise). An observation period began when a Northern Mockingbird flew to the ground to forage and ended when it flew to an elevated position (e.g., tree, post). For each observation bout, we recorded the time spent foraging (sec); the number of WF events; the number of foraging strikes that were successful (i.e., manipulation of prey; usually a “gulp” as described by Remsen and Robinson 1990) and unsuccessful (i.e., no observed manipulation of prey); the type of foraging substrate (open = concrete, pavement, and dirt; or concealing = grass, mulch, under trees and bushes); the habitat type (field = open area with short herbaceous plants, parkland = open herbaceous cover with scattered trees and shrubs, or urban = open space dominated by pavement with interspersed islands of vegetation); the degree of cloud cover (i.e., cloudy, partly cloudy, clear); and the ambient temperature during the observation. For analysis, we compared bouts during the reproductive period (7 March [onset of first active singing] to 15 September [independence of last known fledglings]) to those observed during the non-reproductive period (16 September–6 March). We observed a total of 96 foraging bouts. However, our study population was primarily unbanded. Therefore, in order to avoid problems with pseudoreplication, we included in our analysis only 1 foraging bout from a bird on any 1 territory in any 1 season, for a total of 41 observation bouts during the reproductive period and 14 bouts during the non-reproductive period. To determine if any measured independent variables (i.e., substrate type, habitat type, hours after sunrise, cloud cover, ambient temperature, or time of year [reproductive vs. non-reproductive]) was a predictor of the presence of WF during a foraging bout, we used a forward logistic-regression model. We also performed a linear regression of WF rate (WF/min) with strike rate (strikes/min) for the foraging bouts that contained WF during the reproductive period (n =20 of 41), and a linear regression on WF rate with strike rate success for the reproductive period foraging bouts that included at least 1 prey strike (n = 38). We only observed WF during 1 of the 14 observation bouts during the non-reproductive period; thus, we were unable to conduct similar analyses for these data. Northeastern Naturalist Vol. 26, No. 2 S.K. Peltier, C.M. Wilson, and R.D. Godard 2019 255 To determine if WF behavior occurred in response to a potential predator, we exposed Northern Mockingbirds to 2 models: a common nest predator (a rubber model of Elaphe alleghaniensis [Holbrook] [Eastern Rat Snake]), and a neutral model (a taxidermied model of a male Pheucticus ludovicianus L. [Rose-breasted Grosbeak]) mounted on a small stand). We placed a model in a territory after a Northern Mockingbird had been observed but had moved out of sight of the observer. To assess if our activity alone on the territory provoked WF, we also exposed a subset of Northern Mockingbirds to a “control walk”, which involved walking to a designated spot on the territory and then returning for observation. If a mockingbird returned to the vicinity within 15 min, we noted the number of WF directed towards the model or to the endpoint of our control walk. We excluded from our analysis any Northern Mockingbirds that did not return to the observation vicinity within 15 min; thus, our final sample size was 10 for the Easten Rat Snake, 12 for the Rose-breasted Grosbeak, and 16 for the control walk. As we were unable to meet the minimum requirement (all cells >5) for a chi square test or a logistic regression model, we compared WF responses during the reproductive period to the predator and the neutral models using a Fisher exact test. We conducted all analyses in the PASW statistics package (PASW 2009). Results Mockingbirds displayed WF in 20 of 41 foraging bouts observed during the reproductive period, and only 1 of 14 foraging bouts observed during the nonreproductive period (Fig. 2). Forward linear-regression analysis indicated that time of year was predictive of foraging bouts with and without WF (F1,53 = 8.583, P = 0.002, r2 = 0.123). Observations that occurred during cloudy conditions only occurred in June and July (by coincidence); thus, we excluded the degree of cloud cover from statistical analyses. The other measured independent variables (substrate type, habitat type, ambient temperature, and hours after sunrise) were not reliable predictors of WF. Linear regressions did not identify a relationship between WF rate and prey strikes/min (r2 = 0.073, P = 0.25), or between WF rate and preystrike success (r2 = 0.147, P = 0.19). Northern Mockingbirds only displayed WF to the predator model and then only during the reproductive period (Table 1). During this time period, Northern Mockingbirds displayed WF at the Eastern Rat Snake model in 57% (4 of 7) of the presentations (Fisher exact test one-tailed P = 0.026). Table 1. Number of wing-flashes (WF) to models and control walk during the reproductive and nonreproductive periods. Asterisk (*) indicates that Northern Mockingbirds are more likely to WF to a snake model during the reproductive period, Fisher exact test o ne-tailed P= 0.026. Reproductive (# of Non-reproductive (# of presentations with WF [%]) presentations with WF [%]) Eastern Rat Snake* (n = 10) 4 of 7 (57%) 0 of 3 (0%) Rose-breasted Grosbeak (n = 12) 0 of 8 (0%) 0 of 4 (0%) Control walk (n = 16) 0 of 9 (0%) 0 of 7 (0%) Northeastern Naturalist 256 S.K. Peltier, C.M. Wilson, and R.D. Godard 2019 Vol. 26, No. 2 Discussion Our data show that seasonality plays a significant role in WF behavior in Northern Mockingbirds. Of the 55 foraging observations (out of 96 total) that we were confident were unique individuals, WF occurred at a much higher rate during the portion of the annual cycle that corresponds to their reproductive period. These data support our prediction, provide support for the previous suggestion that WF is confined to warmer months when flying invertebrate prey are common (Hailman 1960b), and add to the body of literature that document WF behavior occurring primarily during the spring and summer months (see Dhondt and Kemink 2008), in correspondence with the Northern Mockingbird’s reproductive period (Farnsworth et al. 2011). Unlike Painted Redstarts and Slate-throated Redstarts that flush and chase more prey when using wing- and tail-plumage flashing than without (Jablonski 1999, Mumme 2002), we found no relationship between Northern Mockingbird WF rate and prey-strike rate. Further, in a previous study of Northern Mockingbirds, Hayslette (2003) found significant negative relationships between WF rate and prey-strike rate. To explain this finding, Hayslette suggested that WF behavior may maximize foraging efficiency by permitting Northern Mockingbirds to assess potential prey and weigh the energetic cost of pursuit against the chance for success (Hayslette 2003). Like Hayslette’s findings, we observed Northern Mockingbirds Figure 2. Percent of foraging bouts with wing-flashing (WF) during the reproductive (n = 41) and non-reproductive (n = 14) time periods. Northeastern Naturalist Vol. 26, No. 2 S.K. Peltier, C.M. Wilson, and R.D. Godard 2019 257 WF while on a variety of substrates, including open habitats (e.g., concrete sidewalks, asphalt driveways) where most arthropod prey would not be well-concealed. As a result of similar observations, Hayslette (2003) proposed that WF may be an innate behavior employed in any habitat where insect prey are not readily visible. Supporting this idea, Jablonski (1999) found that pecking frequency of redstarts was lower when birds foraged with their wings spread than with their wings closed, suggesting redstarts use wing and tail displays more often in areas where prey abundance is low. Although Hayslette (2003) showed a non-significant trend (P = 0.066) in the relationship between ambient temperature and wing-flashing rate in Northern Mockingbirds, our data show that ambient temperature was not a predictor of WF behavior during a foraging bout. These current results do not support our prediction, and it may be that the range of temperatures that occurred during our observations had no effect on the likelihood of invertebrate-prey movement in response to WF. It is also possible that the arthropod species that dominate the diet of Northern Mockingbirds (i.e., orthopterans, coleopterans, hymenopterans, and lepidopterans; Beale et al. 1916) respond differently to white flashes than do dipterans and homopterans, which dominate the diet of other bird species that flash plumage, such as redstart species. Jablonski and Lee (2006) showed that both dipterans and homopterans elicited strong escape responses to the white visual display in the tail and wing plumage of redstart models. To our knowledge, the startle responses of the arthropods that dominate the diet of mockingbirds have not been studied, and it is possible that these arthropods are less responsive, or respond in ways that do not increase strike rates or foraging success in mockingbirds. As proposed by both Brackbill (1951) and Hayslette (2003), and supported by our findings, WF in Northern Mockingbirds may not simply be a behavior mechanism to flush prey. Wing-flashing has been documented in mockingbird fledglings (Allen 1947; Hailman 1960a; Peltier et al., pers. observ.; Sutton 1946) and in 11 other mimid species that lack conspicuous white wing-patches (Burtt et al. 1994), suggesting that WF behavior may be an innate behavior and also an ancestral trait in Mimidae. As suggested by Selander and Hunter (1960) and Dhondt and Kemink (2008), WF may also be a behavioral strategy employed by mockingbirds when confronting a predator, though this possibility had not been tested. Although our sample size was modest, Northern Mockingbirds WF in over half of all presentations of an Eastern Rat Snake model during the reproductive period, and in no other circumstance (neutral model, control walk, or in the non-reproductive time period). While we were not certain of the reproductive stage (e.g., eggs, nestlings or fledglings) of the tested birds, these data do suggest the antipredator role of WF in the reproductive season. It is noteworthy that, although Northern Mockingbirds did direct WF towards the Eastern Rat Snake model, there was only 1 instance when a bird also gave a “hew” call, which is utilized by mockingbirds when mobbing a nest predator or chasing a conspecific (Farnsworth et al. 2011). Given that snakes lack tympanic ears and thus have very limited ability to respond to airborne sound (Christensen et al. 2012), WF might be a more effective anti-predator behavior than vocalization, and could serve as an interspecific predator -deterrent signal. Northeastern Naturalist 258 S.K. Peltier, C.M. Wilson, and R.D. Godard 2019 Vol. 26, No. 2 Conspicuous prey signals that serve to alert predators that they have been detected are utilized by a wide variety of prey species (e.g., Bildstein 1983: white-tail–flagging in Odocoileus virginianus [Zimmermann] [White-tailed Deer]; Murphy 2006: tail wags in Eumomota superciliosa [Sandbach] [Turquoise-browed Motmot]; Rundus et al. 2007: “hot” tail-flagging in Spermophilus beecheyi [Richardson] [California Ground Squirrel] to Crotalus oreganus [Holbrook] [Northern Pacific Rattlesnake]; Tan et al. 2012: abdominal shaking in Apis cerana [Fabricius] [Asian Hive Bee]). It has been assumed that these deterrent signals are associated with a reduction in predatory behavior, but they may also impose a potential cost to the signaler, as the exaggerated movement and the flashing of conspicuous colors advertise the signaler’s location to other undetected predators in the environment. Ruiz-Rodriguez et al. (2013) found that raptors had higher attack rates on model bird species with conspicuous plumage patterns when compared to the same models painted to resemble more camouflaged heterospecifics. It would be valuable to determine if Northern Mockingbird WF increases their vulnerability to common avian predators such as Accipter striatus (Vieillot) (Sharp-shinned Hawk). If WF is costly, it may explain why Northern Mockingbirds in our study only wing-flashed to the Eastern Rat Snake model during the reproductive time period when vulnerable eggs, nestlings, and fledglings were present. It would also be useful to test the responses of Eastern Rat Snakes to models of Northern Mockingbirds that WF with white patches, WF with darkened patches, and those with wings held close to the body. Finally, it would be valuable to examine the incidence of WF by Northern Mockingbirds to live snakes, as other studies suggest that live snakes often evoke stronger responses than snake models (Sherbrooke and Westphal 2006). We provide a potential explanation for the use of WF to predator models, but it remains difficult to explain why Northern Mockingbirds employ WF while foraging. Perhaps the species WF only when they are more food-motivated and, thus, more risk-prone. In such a situation, a potentially risky behavioral strategy that enhances foraging-success rate, even modestly, may be maintained. If this is true, we would predict that there would be a positive correlation between wing-flashing rate and time since last provision to nestlings or to last consumption of a food item. 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