Possible relationships between morphology, territory quality, and skin color of American Kestrels 1

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1 J. Field Ornithol. 77(4): , 2006 DOI: /j x Possile reltionships etween morphology, territory qulity, nd skin color of Americn Kestrels 1 Mrk R. Bostrom nd Gry Ritchison 2 Deprtment of Biologicl Sciences, Estern Kentucky University, Richmond, Kentucky 40475, USA Received 7 April 2006; ccepted 2 June 2006 ABSTRACT. Crotenoid-sed colortion of skin nd plumge hs een found to e correlted with individul qulity in mny species of irds during the reeding seson. However, less is known out the possile role of these signls during the nonreeding seson, prticulrly mong nonpsserines tht defend winter territories. Americn Kestrels (Flco sprverius) re sexully dimorphic rptors tht defend winter territories nd possess crotenoid-sed morphologicl fetures known to e correlted with individul qulity. Much is known out winter territory use nd hitt segregtion y mle nd femle kestrels, ut possile reltionships mong morphologicl fetures, individul qulity, nd hitt qulity hve not een exmined. Our ojective ws to exmine possile reltionships etween morphology, territory qulity, nd skin color of Americn Kestrels. Mle kestrels hd righter skin thn femles, nd the skin color of mle kestrels ws positively correlted with size (wing chord nd til length) nd territoril qulity (hunting territories with less cnopy nd more grss cover). No such reltionships were found for femle kestrels. Skin color ppers to e n honest indictor of qulity for mle Americn Kestrels nd my serve oth intersexul (territory cquisition) nd intersexul (mte choice) functions during the reeding nd nonreeding sesons. SINOPSIS. Posile relción entre l morfologí, clidd del territorio y el color del integumento en Flco sprverius Se h encontrdo que l colorción de plums e integumento, socid l ingestión de crotenoides, está correlciond con l clidd de individuos en muchs especies, durnte l époc reproductiv. Sin emrgo, se conoce poco sore el posile rol de ests señles durnte l époc no-reproductiv, prticulrmente entre pserinos que defienden territorios durnte el invierno. Flco sprverius es un tipo de flcón sexulmente dimorfico que difiende territorio durnte el invierno y tiene estructurs morfológics cuyo pigmento está sdo en crotenoides los cules, suvez, están correlciondos con l clidd de los individuos. Se conoce stnte sore el uso de territorios durnte el invierno y segregción de háitt por prte de mos sexos, pero nos se h estudido l posile relción entre spectos morfológicos, l clidd de los individuos y l clidd del háitt utilizdo. Nuestro ojetivo fue exminr l posile relción entre morfologí, clidd del territorio y color del integumento en los flcones. El mcho de l especie tiene un integumento más rillnte que l hemr y el color de este se correlcionó positivmente con el tmno (lrgo del l y el ro) y l clidd del territorio (territorio de cceri con poco docel y más áres ierts con yers). No se encontró un correlción similr en ls hemrs. El color del integumento prece ser un uen indicdor de l clidd de los mchos y pudier servir pr l dquisición de territorios y l selección de prejs tnto durnte l époc de reproducción como fuer de l mism. Key words: crotenoids, Flco sprverius, individul qulity, integument color, territory qulity Morphologicl fetures such s plumge nd skin color hve een found to e correlted with individul qulity in severl species of irds (Hill nd Montgomerie 1994, Bortolotti et l. 1996, Keyser nd Hill 1999). For exmple, the intensity of colortion (red, yellow, nd ornge) derived from crotenoid pigments ws correlted with nutritionl condition in House Finches (Crpodcus mexicnus; Hill 1991) nd physicl 1 Eugene S. Morton served s proxy editor for this mnuscript. 2 Corresponding uthor. Emil: gry.ritchison@ eku.edu condition in Americn Kestrels (Flco sprverius; Bortolotti et l. 1996, Negro et l. 1998). Becuse crotenoid pigments cnnot e synthesized y vertertes nd must e ingested, Hill nd Montgomerie (1994) hypothesized tht mle House Finches in etter condition (i.e., righter mles) were etter le to cquire foods rich in crotenoids thn mles in poor condition. These uthors found correltion etween plumge rightness nd til fether growth rtes, supporting their hypothesis tht righter plumge ws correlted with nutritionl condition. Morphologicl indictors of qulity cn reduce intrspecific competition nd influence mte choice. For exmple, Mteos nd Crrnz C 2006 The Author(s). Journl compiltion C 2006 Assocition of Field Ornithologists 392

2 Vol. 77, No. 4 Skin Color of Kestrels 393 (1997) experimentlly rightened nd dulled the plumge of mle Ring-necked Phesnts (Phsinus colchicus) equl in ody weight, trsus length, spur size, frequency of wttle displys, nd rnk. Dull mle phesnts were suordinte to righter individuls, suggesting tht ssessing conspecific s fighting ility through plumge rightness llowed individuls to void confronttions (Mteos nd Crrnz 1997). Similrly, Studd nd Roertson (1985) found tht territoril Yellow Wrlers (Dendroic petechi) evluted the possile thret posed y conspecific intruder y ssessing the mount of rown streking on n intruder s rest. Intruders with more rown streking elicited ggressive responses from the territory holder, while those with less streking did not. Such ssessment llowed resident Yellow Wrlers to determine if n intruder ws thret without wsting energy or risking possile hrm y confronting suordinte (Studd nd Roertson 1985). Americn Kestrels re sexully dimorphic rptors tht defend winter territories nd possess crotenoid-sed morphologicl fetures shown to e correlted with individul qulity (Bortolotti et l. 1996, Negro et l. 1998). Much is known out winter territory use nd hitt segregtion y mle nd femle kestrels (Koplin 1973, Mills 1976, Smllwood 1987, 1988, Ardi nd Bildstein 1997), ut possile reltionships mong morphologicl fetures, individul qulity, nd hitt qulity hve not een exmined. For exmple, higher qulity kestrels my otin higher qulity winter rnges nd, thus, spend less time nd energy hunting. Smllwood (1988) found correltion etween the qulity of kestrel forging hitt nd time spent hunting, with those in etter qulity hitt (hunting sustrte contining grsses nd weedy fors <25 cm in height) producing pellets of greter mss y noon thn irds in lower qulity hitts (Smllwood 1988). By dys end, kestrels in higher nd lower qulity sites cquired similr quntities of prey, ut Smllwood s (1987, 1988) results indicte tht hitt qulity my hve influenced dily ctivity udgets. Tht is, kestrels in etter hitt my spend less time forging nd, perhps, more time on nonhunting ctivities (e.g., resting). The ojective of our study ws to exmine the possile reltionship etween hitt qulity nd individul qulity in mle nd femle Americn Kestrels in centrl Kentucky. METHODS Kestrels were studied from Octoer 2000 April 2001 t the Blue Grss Army Depot (BGAD) nd djcent res in Mdison County, Kentucky. The BGAD consists of 5907 h, primrily composed of psture with trees nd woodlnds interspersed throughout. Mle (N = 19) nd femle (N = 18) kestrels were cptured from 17 Novemer 2000 to 22 Mrch 2001 using l-chtri trps (Berger nd Mueller 1959) ited with mice. Ech kestrel cptured ws fitted with numered luminum nd nd unique comintion of colored-plstic nds to permit individul recognition. Stndrd morphologicl mesurements, including wing chord, trsus length, til length, nd mss, were determined. In ddition, one rectrix (fourth from the right) ws plucked from ech kestrel so the men width of dily growth rs ( mesure of nutritionl condition; Hill nd Montgomerie 1994) could e determined. A technique similr to tht descried y Bortolotti et l. (1996) ws used to score the color of unfethered ceres, lores, nd trsi. This included six-color chrt consisting of Munsell color chips rnging from 1 (ple yellow) to 6 (red-ornge). These colors were chosen ecuse they est represent the incresing intensity in crotenoid colortion (Tle 1). Munsell color chips re chrcterized y three spects: (1) the hue defined s the qulity y which the color is distinguished from other colors, (2) the vlue defined s the qulity of the color y which light Tle 1. The six-color option chrt used to score the color of the skin of the cere, lore, nd trsus of mle nd femle Americn Kestrels. Color score Hue Vlue /Chrom c 1 7.5y d 8.5/ y 8.5/ y 8.0/ y 7.0/ yr e 7.0/ yr 6.0/12 Hue is defined s the qulity y which one color is distinguished from nother. Vlue is defined s the qulity y which light color is distinguished from drk color. c Chrom is defined s the qulity tht distinguishes the difference from pure hue to gry shde. d y = yellow. e yr = yellow-red.

3 394 M. R. Bostrom nd G. Ritchison J. Field Ornithol. Fll 2006 nd drk colors re distinguished, nd (3) the chrom, or the color qulity tht distinguishes the difference from pure hue to gry shde. As the color score increses from ple yellow to red-ornge, the vlues of the color chips increse (i.e., incresing rightness) s do the hues (i.e., tending towrd red nd wy from yellow indicting incresed crotenoid pigment), with incresing chrom scores indicting more pure color. The scores for ech ody prt were dded together for totl score, with high score indicting rightness (high qulity) nd low score indicting dullness (low qulity). Oservtions of focl kestrels were conducted from Jnury to April An oservtion egn when focl kestrel ws locted nd lsted until the ird ws lost from view or hd een oserved for min. During ech oservtion period, ll hunting perches from which ttcks were initited were identified. Perch site nlyses were conducted following the methods of Smllwood (1987). For ech nlysis 1-h circulr plot ws plced round perch used y focl kestrel. Within ech 1-h circulr plot, 20 sites were divided evenly into four qudrnts, nd rndomly distriuted in ech qudrnt using rndom numer tle nd numered circulr grid of the plot. The grid ws numered 1 through 9 for ech qudrnt oth down nd cross. Numers were chosen from the rndom numer tle y dropping two pieces of rice on the tle nd the numers most covered y the rice were used. At ech of the 20 sites 1-m 2 qudrt ws plced on the ground to ssure the sme size ws mesured for ech site. For ech, site the hitt ws chrcterized using eight prmeters: (1) type of ground vegettion (grss, fors, woody vegettion, or no vegettion), (2) condition of ground vegettion (<33% ded, >33% ut <67% ded, or >67% ded), (3) verge height of ground vegettion, (4) presence of tree or shru cnopy directly over smple point (no cnopy, on the edge of dense shru (>1 shru, ove meter)/woodlot opening, under solitry tree or shru, or within dense shru (>1 shru, ove meter)/woodlot with closed cnopy), (5) species of cnopy plnts, (6) condition of cnopy plnt (live with folige, dormnt without folige, or ded), (7) cnopy height (ny portion of tree or trees 2mover the plot; clinometer ws used to determine heights) nd tree dimeter, nd (8) lnd use. Lnd-use ctegories included old field (presence of shrus, trees, nd grss >1 m), wter, continully mintined vegettion (vegettion regulrly mowed to keep vegettion 10 cm in res such s rodsides ner uildings), vegettion mintined nnully (vegettion mowed once or twice yer in June, July, or August), vegettion mintined, ut not nnully (mowed in the pst ut not on n nnul sis, vegettion >1 m high with few or no trees >1 m tll), grzed (cttle present), woodlot ( four trees 3 m in height in close proximity, with rnches touching or overlpping), pved rod, unpved rod, uilding (not including unkers due to vegettion covering them), or some comintion of these ctegories (such s grzed nd mintined nnully). Reltionships etween fether growth rtes nd skin color were exmined using correltionl nlysis, nd Wilcoxon tests were used to exmine differences in morphometric mesurements, growth r width, nd totl color score etween mle nd femle kestrels. Discriminnt function nlysis ws used to determine if the chrcteristics of kestrel perch sites vried with skin color. Bsed on skin color, femle kestrels were ctegorized s either dull or right, nd mles s dull, medium, or right. These ctegories were determined sed on overll men color scores for femles nd mles, s well s gps etween scores. For mles, the men color score ws 12.8 (rnge = 9 17) nd no mle hd color scores of 11 or 15. Thus, color scores of 10 or less were ctegorized s dull, scores of s medium, nd 16 or more s right. For femles, the men color score ws 9.2 (rnge = 5 15) nd no femle hd color score of 11 nd, therefore, color scores of 10 or less were ctegorized s dull nd scores of 12 or more s right. Vriles importnt in discriminting etween mles nd femles in these ctegories were determined y stepwise discriminnt nlysis (ckwrd procedure). The cross-vlidtion technique ws then used to evlute model clssifiction efficcy (Willims et l. 1990). Cohen s nd its Z vlue were clculted to test model performnce (Titus et l. 1984). All nlyses were performed using the sttisticl nlysis system (SAS Institute 1999). RESULTS Mle nd femle Americn Kestrels differed in the color of the skin on the cere, lore, nd trsus.

4 Vol. 77, No. 4 Skin Color of Kestrels 395 Tle 2. Comprison of morphometric mesurements of mle nd femle Americn Kestrels. Mle Femle Vrile z vlue P vlue Men SE N c Men SE N c Mss(gm) 4.08 < Bill (mm) Trsus (mm) Wing chord(mm) Til (mm) Color score d Growth r width (mm) Wilcoxon tests. Stndrd error. c Smple sizes re unequl ecuse we did not otin ll mesurements for ll individuls. d Color score equls the sum of cere score + trsus score + lore score. Ech of these res ws scored for ech kestrel nd the three vlues summed for n overll color score. The overll color scores for mles (N = 18) nd femles (N = 18) differed significntly (z = 3.25, P = ), with men of 12.8 ± 0.7 (SE; rnge = 9 17) for mles nd 9.2 ± 0.6 (SE; rnge = 5 15) for femles. In ddition, femle Americn Kestrels were lrger thn mles, with femles weighing significntly more thn mles nd hving significntly longer ills, wing chords, nd tils (Tle 2). However, mle nd femle kestrels did not differ in either trsus length or men width of rectrix growth rs (Tle 2). We found few significnt correltions etween morphology nd either growth r width or skin Tle 3. Correltions etween skin color nd morphologicl chrcteristics of femle Americn Kestrels. Correltion (vrile vrile) r s vlue P vlue Color score wing chord Color score trsus length Color score mss Color score til length Cere color score rectrix growth rte Cere color score wing chord Lore color score wing chord Trsus score nd wing chord Rectrix growth rte mss Rectrix growth rte color score Bonferroni-corrected; significnce ccepted t P Color score equls the sum of cere score + trsus score + lore score. color for femle kestrels (Tle 3). We found significnt correltion etween cere score nd wing chord (r s = 0.55, P = 0.018). However, correltions etween trsus score nd wing chord (r s = 0.22, P = 0.37) nd etween lore score nd wing chord (r s = 0.25, P = 0.31) were not significnt. We found no significnt correltions etween totl color score nd til length (r s = 0.18, P = 0.48), trsus length (r s = 0.09, P = 0.74), or mss (r s = 0.30, P = 0.25), respectively. For mle kestrels (Tle 4), the correltion etween growth r width nd totl color score pproched significnce (r s = 0.45, P = 0.059). In ddition, we found significnt correltions etween totl color score nd wing chord (r s = 0.65, P = 0.004) nd totl color score nd til length (r s = 0.59, P = ). Lrger mles Tle 4. Correltions etween integument color nd morphologicl chrcteristics of mle Americn Kestrels. Correltion (vrile vrile) r s vlue P vlue Color score wing chord Color score trsus length Color score mss Color score til length Trsus color score rectrix growth rte Trsus color score wing chord Rectrix growth rte mss Rectrix growth rte color score Color score equls the sum of cere score + trsus score + lore score. Bonferroni-corrected; significnce ccepted t P

5 396 M. R. Bostrom nd G. Ritchison J. Field Ornithol. Fll 2006 Tle 5. Vriles permitting est discrimintion mong hunting res used y mle Americn Kestrels with dull, medium, nd rightly colored skin. Hitt vrile Prtil R 2 vlue F vlue P vlue % Grss % Woody vegettion % No cnopy % Edge of dense shrus/woodlot opening % Under solitry tree/shru % Within dense shrus/closed cnopy % Live vegettion % Ded vegettion %Oldfield % Grzed woodlot % Mintined nnully/grzed % Woodlot % Pved rod % Unpved rod Men vegettion height Color scores (sum of cere score + trsus score + lore score) for ech ctegory: dull = 9 or 10, medium = 12 14, or right = 16 or 17. (sed on wing chord nd til lengths) were righter. Correltions etween totl color score nd other possile mesures of mle size, trsus length (r s = -0.12, P = 0.66), nd mss (r s = 0.20, P = 0.43), were not significnt. We found no differences in the chrcteristics of res used y hunting mle nd femle Americn Kestrels (Wilk s = 0.44, F 29,38 = 1.66, P = 0.072). Similrly, there ws no difference etween dull (totl score 10; N = 14) nd right (totl score 12; N = 4) femle kestrels in the chrcteristics of hitts used for hunting (Wilk s = 0.14, F 5,29 = 1.07, P = 0.52). For mle kestrels, however, we found significnt difference (Wilk s = 0.01, F 14,52 = 2.31, P = 0.044) in the chrcteristics of hitts used y dull (totl score of 9 or 10; N = 18), medium (totl score of 12 14; N = 5), nd right (totl score of 16 or 17; N = 12) individuls. Stepwise discriminnt nlysis reveled tht 15 vriles permitted est discrimintion mong hitts used y mles in these three ctegories (Tle 5). A model including ll 15 vriles correctly clssified 86% of ll hunting res used y mles into the pproprite ctegory. This, however, ws only 15% etter thn ctegorizing y chnce lone (Cohen s Z = 1.70, P = 0.088). Most incorrect clssifictions were for medium individuls (only 2 of 5, or 40% were correctly clssified). Excluding those five mles from the nlysis, ll 12 right mles nd ll 18 dull mles were correctly clssified (100% etter thn e chnce lone; Cohen s Z = 5.29, P < ). Exmintion of these 15 vriles indictes tht res used y righter mle kestrels tended to e grzed nd mintined (mowed) hitts with more grss cover nd less cnopy thn res used y dull individuls. DISCUSSION Mle Americn Kestrels in our study hd righter skin thn femles. Similrly, Negro et l. (1998) reported tht mle Americn Kestrels exhiited righter skin color thn femles during oth the reeding nd nonreeding sesons nd, further, tht skin color ecme righter during the reeding seson. Mle Eursin Kestrels (Flco tinnunculus) were lso found to hve righter skin color thn femles during the reeding seson (Csgrnde et l. 2006). Such sesonl vrition would e expected in sexully selected trit nd, further, suggests tht kestrels my hve the ility to regulte their skin color (Negro et l. 1998). The skin color of mle Americn Kestrels in our study ws correlted with mesures of oth individul nd territoril qulity, with righter mles nd hunting in res with more, ut shorter, grss cover nd less cnopy cover. Skin

6 Vol. 77, No. 4 Skin Color of Kestrels 397 color is likely n ccurte indictor of current condition (Johnson et l. 1993, Bortolotti et l. 1996). Johnson et l. (1993) suggested tht crotenoid pigmenttion in the skin of irds ws n indictor of short-term chnges in physiologicl condition ecuse irds generlly do not store crotenoid pigments in the skin due to the lck of chromtophores (Brush 1990). Even though fethers my contin crotenoid pigments, these pigments hve een deposited nd re not stored in wy tht llows them to chnge s result of short-term chnges in physiologicl condition (Brush 1990). The correltion etween skin color of mle Americn Kestrels nd rectrix growth rtes in our study pproched significnce, suggesting tht mle skin color my e n honest indictor of nutritionl condition nd, perhps, individul qulity. Previous studies hve reveled tht rectrix growth rtes re positively relted to nutritionl condition in numer of species (e.g., Gru 1989, Jenkins et l. 2001), nd the reltionship etween condition nd crotenoidsed colortion hs lso een demonstrted in wide vriety of species (Hork et l. 2001, Sks et l. 2003). In Americn Kestrels Bortolotti et l. (1996) found significnt correltion etween plsm crotenoid levels nd plsm protein levels, suggesting reltionship etween crotenoid levels nd kestrel s condition. In ddition, Csgrnde et l. (2006) found tht the skin color of mle Eursin Kestrels ws correlted with the numer of prey delivered to the nest, suggesting tht mles with righter skin were etter hunters. We found tht mle Americn Kestrels with righter skin hunted in res with more, nd shorter, grss nd with less cnopy cover thn did mles with duller skin. Ares with these chrcteristics re likely higher qulity hunting sites ecuse shorter vegettion increses prey detectility (Bechrd 1982, Tolnd 1987). Tolnd (1987) found tht Americn Kestrels preferred distured grsslnds (mowed, grzed, nd hrvested) ecuse the shorter vegettion incresed detectility of prey. Similrly, Bechrd (1982) found tht Swinson s Hwks (Buteo swinsoni) fvored hitts with less vegettive cover (hrvested crop fields) ecuse less cover incresed the chnces of prey detection. Vegettion cover my e more importnt thn prey density in the selection of forging sites y Swinson s Hwks (Bechrd 1982). If res with shorter vegettion re lso importnt for kestrels, the presence of righter mle kestrels in such res further suggests tht skin color of mles is n indictor of qulity. Mle kestrels with righter skin my e dominnt to those with duller skin nd, therefore, might e le to otin nd defend higher qulity hunting sites. Although we found position correltion etween skin color nd pprent qulity of hunting sites for mle Americn Kestrels, no such correltion ws found for femle kestrels. One possile explntion for such results is tht femle kestrels re dominnt to mles, regrdless of skin color, nd, s result, must compete only with other femles for ccess to hunting res. Mle kestrels, on the other hnd, would then compete with ech other for ccess to the remining res. If so, femle kestrels re more likely to e oserved hunting in higher qulity res. In support of this conclusion, Aorn (1989) found tht femle Americn Kestrels did tend to dominte mles nd, in ddition, tht hevier kestrels tended to dominte lighter ones. In summry, skin color of mle kestrels ppers to represent n honest indictor of qulity (nutritionl condition nd size). As such, skin color could potentilly serve oth intrsexul (territory cquisition) nd intersexul (mte choice) functions during the reeding nd nonreeding sesons. ACKNOWLEDGMENTS We thnk the Estern Kentucky University Reserch Committee for finncil support, nd G. Bortolotti, J. Smllwood, K. Bildstein, nd n nonymous reviewer for comments nd suggestions tht improved the mnuscript. LITERATURE CITED ABORN, D. A Reversed size dimorphism, determinnts of intrspecific dominnce, nd hitt use y Americn Kestrels (Flco sprverius) wintering in South Crolin. M.S. thesis. Clemson University, Clemson, SC. ARDIA, D. R., AND K. L. BILDSTEIN Sex-relted differences in hitt selection in wintering Americn Kestrels, Flco sprverius. Animl Behviour 53: BECHARD, M Effect of vegettive cover on forging site selection y Swinson s Hwks. Condor 84: BERGER, D. D., AND H. C. MUELLER The lchtri: trp for irds of prey. Bird-Bnding 30:

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