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P0395-P0400.Pdf TheCondor95:395-400 0 The Cooper Omthological Soaety 1993 AN EXPERIMENTAL TEST OF THE CONTRASTING-COLOR HYPOTHESIS OF RED-BAND EFFECTS IN RED-WINGED BLACKBIRDS ’ KAREN J. METZ AND PATRICK J. WEATHERHEAD Department of Biology, Carleton University,Ottawa, Ontario KlS 5B6, Canada Abstract. We performed an experiment to investigate effects of red leg bands on the behavior of male Red-winged Blackbirds(Agelaiusphoeniceus). We presentedmodels having either black, blue, or red leg bands to territorial male Red-winged Blackbirds to test the hypothesisthat any color of band that contrastswith the color of the legsmakes an individual appear abnormal or unhealthy and therefore subject to attack. Overall, territorial males respondedequally aggressivelyto the black- and blue-banded models, but spent more time at distancesgreater than 10 m, displayedat lower intensities, and took longer to attack when the model was given red bands. Thus, red bands appearedto make the model initially more threatening to territorial male Red-winged Blackbirds. These results do not support the contrasting-color hypothesis and suggestthat the effect of red bands is attributable to the bands matching the color of the male’s epaulets. The failure of the contrasting-color hy- pothesisalso leaves unresolvedthe different outcomesof one previous experiment showing a negative effect of red bands, and two analysesof long-term banding studiesthat detected no effect of red bands. Key words: Red-wingedBlackbird; Agelaius phoeniceus;epaulets; colored bands. INTRODUCTION than red-banded males with smaller epaulets We recently demonstrated that red leg bands se- (Metz and Weatherhead 199 1). The causeof the verely reduced the ability of male Red-winged territory loss appeared to be increased and more Blackbirds(Ageluiusphocnicrus) to maintain their persistent intrusion by other males, particularly territories, unlike black bands which had no no- territorial neighbors. Thus, we proposedthat red ticeable effect on male behavior (Metz and bands acted as secondary sexual traits in con- Weatherhead 199 1). That study added to grow- junction with the males’ red epaulets, the com- ing evidence that colored leg bands can affectbird bined effect of which was to make red-banded behavior (Burley 1981, 1985, 1986a, 1986b; males appear to be signaling more aggressively Burley et al. 1982; Brodsky 1988; Hagan and than their competitive ability warranted. The in- Reed 1988; Holder 1990). Because colored leg consistency between signal and ability caused bands are widely used in ornithological research, thesemales to be challenged.This effectwas most it is important that we understand the circum- pronounced in males with large epaulets and was stancesthat causecolor bands to affect behavior. most noticeable to their neighbors. Color-band In addition to the practical concerns, under- effects reported by Brodsky (1988) Hagan and standing color-band effects may also shed light Reed (1988) and Holder (1990) also involve col- on questions concerning the evolution of colored ors that matched secondary sexual traits, and in secondary sexual traits in birds (Burley 1986b). the last two studies, the effect of those bands was Here, we present an experiment that tests one of also negative. the hypothesesproposed to explain the effect of We also proposedother hypothesesthat might red bands on male Red-winged Blackbirds. explain the negative effect of red bands on male In addition to the general result that red leg Red-winged Blackbirds (Metz and Weatherhead bands caused some males to lose territories, we 1991). Because epaulets are coverable (Hansen also observed that red-banded males with larger and Rohwer 1986) in Red-winged Blackbirds epaulets were more likely to lose their territories (whereas bands are not), it may have been the exposure of an aggressivesignal under inappro- priate circumstances rather than the size of the I Received8 December1992. Accepted 21 Decem- signal per se that made red bands detrimental. ber 1992. An experiment in which feather clipping caused 13951 396 KAREN J. METZ AND PATRICK J. WEATHERHEAD male Red-winged Blackbirds to exposetheir ep- those models did not have leg bands, previous aulets continuously suggestedthat the ability to experience with a model blackbird could reduce cover epaulets is important for some activities the males’ aggression in subsequent exposures (e.g., trespassing on neighbors’ territories), but (Hansen and Rohwer 1986). Therefore, we an- doesnot causemales to lose their territories (Metz alyzed their responsesseparately from those of and Weatherhead 1992). Thus, the inability to naive males. cover red bands appears insufficient to explain Aggressive territory owners can destroy taxi- why red bands are detrimental. dermic models in a matter of minutes (Rohwer Another hypothesis for the negative effect of 1978, pers. observ.). This can causeserious prob- red bands, and that which we test here, is that lems in keeping the stimulus the same when pre- the bands are detrimental simply because they senting the model to several males in succession. contrast with the color (black) of the legs.A con- Therefore, we designed a model that was virtu- trasting color may make males appear abnormal ally indestructible by a male Red-winged Black- or unhealthy and thus, for some reason (e.g., they bird. The model’s body was made from black are less threatening), provoke an attack. If this cotton material stuffed with cotton balls. We fas- hypothesis is correct, then any color that con- tened a male Red-winged Blackbird wing with trasts with the color of the legs should provoke the epaulet fully exposedto each side of the cot- attack in Red-winged Blackbirds. This hypoth- ton body. A male Red-winged Blackbird head esis could also explain the failure to find any was covered with the same black material as on negative effect of red bands in retrospectiveanal- the body so that only the bill was exposed and yses of two long-term studies of banded popu- was attached to the body. Pins with round black lations (Beletsky and Orians 1989, Weatherhead heads of an appropriate size were used as eyes. et al. 1991). In both studies, all birds received Pairs of male Red-winged Blackbird legs given bands (only some of which were red) that con- six (three per leg) royal blue, black, or red plastic trasted with the color of their legs. Therefore, leg bands could also be fastened with Velcro@ to regardlessof the color of their bands, all birds the body. Thus, the only feature of the model would have been similarly affected,and no effect that varied when presented to owners was the specific to red bands would be expected. We test color of the model’s leg bands. The color of the the contrasting-color hypothesis by quantifying red bands matched the color of the model’s ep- the response of territorial male Red-winged aulets. Red bands and the model’s epaulet color Blackbirds to models with either contrasting (red were scored as Inter-Society Color Council-Na- or blue) or noncontrasting (black) color bands. tional Bureau of Standards (ISCC-NBS) number 36 (Munsell renotation 9.2R 3.9/l 2.1). The color METHODS of the blue bands was scoredas ISCC-NBS num- We conducted this experiment in three cattail ber 182 (Munsell renotation 3.OPB 4.3/6.8). The marshes located within 40 km of the Queen’s blue bands appeared to us to present the same University Biological Station in eastern Ontario contrast to the legs as did the red bands. The from 26 April to 22 May 1990. We presented color of the black bands was ISCC-NBS number territorial males with a male Red-winged Black- 267 (Munsell renotation N 0.8). The black bands bird model given red, blue, or black bands. Ap- matched the color of the legs and thus were dif- proximately half the territorial males were “na- ficult for us to see at any distance. ive,” never having been exposedpreviously to a Model presentations were conducted between model blackbird and not used in other experi- 06:OOto 09:OOhours d.s.t., the time when males ments. The remaining “experienced” males were were most active. We placed the model near the also part of another experiment in which we center of a male Red-winged Blackbird’s terri- clipped either the black feathers that are used by tory while the owner was present and then ob- males to conceal their epaulets, causing the ep- served the response from 30-50 m away for 5 aulets to be permanently exposed( “experienced- min. Male Red-winged Blackbird songswere not clipped”), or an equivalent number of contour played during the model presentations. feathers that did not alter the males’ appearance We measured the following aspectsof the own- (“experienced-controls”). In the course of these ers’ behavior during the model presentations (af- treatments these males had been captured using ter Rohwer 1978): (1) T ls’-the latency in sec- model blackbirds and song playbacks. Although onds to the first time an owner reacted to the BAND-COLOR EFFECTS ON BLACKBIRDS 397 x . x X Xl xtf X 00% x QIX X0 .‘.!qj 0 X .’ o 00 X 0 x . 0 X0 .O 0 l X - l 0 0 0 .l . x Xk 0 X 0 . 0 0 0 0 -3 -2 -1 2 9 4 FURCTION1 l FIGURE 1. Scatterplotof territorial males’ responsesto the model with red (open circles), black (X s), or blue (closed circles) bands using the males’ discriminant function scoresfor Function 1 (time to attack; proximity to model) and Function 2 (song spread rate and intensity). model (up to 300 set). Reactions included flying respond differently upon subsequent presenta- closer to the model, or directing a song spread tions. We randomly assignedwhether an owner display at the model; (2) T HIT-the latency in was presented with the red-, blue-, or black- seconds to the first time an owner struck the banded model.
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