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The Auk 113(4):802-810, 1996 INFLUENCEOF THE TRAILING-EDGENOTCH ON FLIGHT PERFORMANCE OF GALLIFORMS SERGEI V. DROVETSKI • BurkeMuseum and Department of Zoology,University of Washington,Seattle, Washington 98195, USA ABsTRACT.--Trailing-edgenotches, formed by shortenedfirst secondaries,characterize the wings of most galliforms. I investigated the function of these notches with comparative measurementsof notch size taken from extended-wing specimensand with experimental studiesof model wings of four representativespecies. Pheasants, quail, and turkeys,all of which use flight to escapepredators, have wide wings and deep notches.Grouse with dark flight muscleshave long, narrow wings with small trailing-edge notchesand typically fly relatively long distancesfrom one foraging site to another. Grousewith light coloredflight muscleshave short,broad wings with large trailing-edgenotches and mostlyfly from ground to canopyor from branchto branch to reachtheir food. Model wings of two pairsof galliforms with different wing shapeswere used in the experiments.White-tailed Ptarmigan(Lagopus leucurus)and Sage Grouse(Centrocercus urophasianus) have small notches,high aspectratios, relatively heavy wing loadings,low maximum lift coefficients,and dark pectoralmuscles. In contrast,Wild Turkey (Meleagrisgallopavo) and California Quail (Callipeplacalifornica) have deep notches,low aspectratios, relatively light wing loadings,high lift coefficients,and light colored pectoral muscles.Experiments using model wings in a water flow tunnel show that the trailing-edgenotch increasesthe maximum lift-to-drag ratio and stabilizesairflow around the wing, but reducesthe maximumlift coefficient.Thus, the trailing-edgenotch increases performancein vertical and slow flight but reducesefficiency in level flight. Sucha function is consistentwith the suite of differencesthese birds show in musclecolor, wing shape,and predominantmode of flight. Received17 November1995, accepted 27 February1996. BIRD WINGSEXHIBIT morphological adapta- ed. However, only Shestakova(1971) has noted tions for different kinds of flight (Rayner 1988, the existenceof this notch in variousgalliforms Norberg 1989).Regardless of the species,slots and some gulls. between the primaries increasethe lift-to-drag In this paper, ! presentcomparative data on ratio by increasinglift and reducing drag (es- the size of the trailing-edge notch for 31 species peciallyinduced drag) that resultsfrom deflec- of galliforms. I also present resultsof experi- tion of an air streamaround a tilted wing. Such mentsthat showhow this notchinfluences glid- conclusionsabout the functionalsignificance of ing performancein the wings of four species wing slotscome primarily from the established with different wing shapes. correlation between deep slotting and slow, level flight that characterizesbirds with wings MATERIALs AND METHODS that are broad at the tip. Wind-tunnel experiments supportthese conclusions(Vinogradov Measurementsof wing length, wing breadth, and 1951; Hofton 1978; Tucker 1993, 1994). trailing-edgenotch size were taken from 220 extended-wing specimensof 31 galliform species(Table 1). Galliformshave deepslots between their pri- I calculated notch size (in %) as: maries and a large alula, but they rarely have been used as subjectsfor aerodynamicstudies (WS - WSs•)/WB, (1) (Shtegman 1953, Shestakova1971). Further- where WBs•is the distancebetween the leading edge more, no study of the aerodynamicsof galli- of the wing and the tip of the first secondary,and forms hasaddressed the functional significance WBis wing breadth measuredfrom the leading edge of the large notch on the trailing edge of the of the wing to the tip of the fifth secondary.I chose wing that is formed by a short first secondary. the fifth secondaryfor these measurementsbecause This feature is exhibited by all galliforms and in somebirds (e.g. turkeys)the wing notch is formed is quite evident when the wing is fully extend- by severalshortened secondary feathers. Wing length is the distancefrom the proximal end of the humerus to the tip of the longest primary, measuredalong a line parallel to the leading edge of the wing. • E-mail: [email protected] Throughout this paper, meansare reported + I SD. 802 October1996] FlightPerformance and the Wing Notch 803 Four speciesof galliformswere chosenfor flight- TABLE1. Trailing-edge notch size and wing length- performanceexperiments based on extremesof wing to-breadth ratio of galliforms. Values are means shape (see Fig. 1) and body size within the order: (with SD in parentheses). White-tailed Ptarmigan ([Lagopusleucurus]; Tetraoni- nae; subadultmale specimen);Sage Grouse ([Centro- Wing cercusurophasianus]; Tetraoninae; adult male); Wild Notch size length-to- (% of wing breadth Turkey ([Meleagrisgallopavo]; Meleagridinae; adult fe- Species n breadth) ratio male); and California Quail ([Callipeplacalifornica]; Odontophorinae;adult male).I refer to themas "mod- Turnicidae el" species.Other speciesof galliformsprovide more Turnix sylvatica 3 12.36 (4.93) 1.77 (0.04) extreme examplesof wing-shapevariation, but my Phasianinae choiceswere limited by the availability of frozen Tetraogallushimalayensis 1 18.14 1.81 specimensat the University of Washington Burke Alectorischukar 3 36.62 (3.54) 1.69 (0.01) Museum for use in creating modelsof wings. Francolinussephaena 3 35.45 (1.60) 1.62 (0.02) I measuredflight performanceby steady-state(con- F. africanus 4 24.98 (2.29) 1.86 (0.05) stant velocity) lift and drag characteristicsof various F. swainsonii 2 47.34 (5.64) 1.57 (0.01) wings.Active flight in thesespecies may not be char- Perdixperdix 6 30.17 (2.34) 1.91 (0.01) acterized by this particular dynamic condition, but P. dauurica 1 36.36 1.78 any differencesin the coefficientsassociated with wing Coturnix coturnix 3 21.57 (2.04) 2.25 (0.05) Lophuraignita 1 35.71 1.58 lift and drag are presumedto apply to flapping, at Gallusgallus 3 38.11 (2.67) 1.48 (0.07) least for fast forward flight. Lift (C•) and drag (Cd) Phasianuscolchicus 13 30.86 (3.20) 1.71 (0.10) coefficientsare defined by the following relation- ships: Odontophorinae Colinusvirginianus 15 32.49 (3.76) 1.61 (0.05) C, = L/(0.5 p SU2), and (2) Callipeplasquamata 2 35.06 (3.46) 1.63 (0.07) C. californica 9 31.84 (3.76) 1.66 (0.05) cd = D/(0.5 p STY2), (3) C. gambelii 2 37.37 (0.58) 1.62 (0.01) where L is the measured lift force, D is the measured Meleagridinae drag force,• is the densityof the fluid medium, S is Meleagrisgallopavo 4 31.40 (2.04) 1.47 (0.10) the plainform area of the wing, and U is the fluid Tetraoninae(light and intermediate velocity relative to the wing. Lift and drag coefficients flight muscles) were measured for model wings. Models were cut from 0.2-mm thick brass foil and soldered to a metal Dendragapusfalcipennis 2 26.50 (3.23) 1.95 (0.11) D. canadensis 10 21.82 (4.29) 1.95 (0.09) rod 2.5 mm in diameter and about 130 mm long. All D. obscurus 19 23.24 (3.31) 1.90 (0.07) modelshad a width of 30 mm (length varied from 46 Bonasabonasia 14 24.52 (2.67) 1.94 (0.07) to 62 mm depending on species).Each model was B. umbellus 22 28.94 (2.49) 1.88 (0.10) slightly bent around the axis of the metal rod, and Tetraoninae(dark flight muscles) the spacebetween the leading end of the model wing Lagopuslagopus 21 22.09 (1.89) 2.09 (0.05) and the rod wasfilled with glue. The bendingcreated L. mutus 14 20.68 (3.08) 2.35 (0.08) camberin the models.The top of the curvature was L. leucurus 8 19.60 (2.86) 2.12 (0.09) 10 mm behind the leadingedge of a modelwing, and Tetrao tetrix 1 18.87 2.08 the height of the curvature,measured as the distance T. urogallus 3 20.67 (1.29) 2.05 (0.16) from a line connectingthe leading and trailing edges T. parvirostris 10 15.17 (2.52) 2.24 (0.11) of a model wing to the top of the curvature, was Centrocercusurophasi- approximately4 mm. The patternsused for preparing anus 10 18.06 (3.54) 2.24 (0.16) the modelswere images(reduced by photocopy)of Tympanuchusphasianel- lus 4 19.25 (2.49) 2.16 (0.05) freshly thawedwings that had beenpinned in a fully T. cupido 7 20.76 (3.17) 2.05 (0.10) extendedposition. Lift and drag coefficientsare functionsof the Reyn- olds number: tunnel. The flow tunnel provided a uniform flow of Re = UL/•, (4) relatively low turbulence intensity (ca. 5%). The working section of the tunnel was square in cross where U is definedas above,L is the length of the section,with sides of 0.2 m and a length of 1.2 m. wing chord, and v is the kinematic viscosityof the The flow in the working sectionhad all four bound- fluid medium of the wing. Consequently,scale mod- aries fixed. During the measurementsI placed each elswere prepared so that in the testingapparatus (see model such that its center was in the center of the below),each model had a Reynoldsnumber relatively working section. Apart from the model, there was similar to that of real wings. only a piece of rod approximately7 cm long in the Lift and drag forceswere measuredin a water flow flow. This rod connected the model to the force trans- 804 Sm•G•V. DItOVETSKI [Auk,Vol. 113 FIG.1. Extended-wingspecimens used as models for the experiments.White-tailed Ptarmigan (Lagopus leucurus;upper left); Sage Grouse (Centrocercus urophasianus; upper right); c31ifornia Quail (Callipepla californica; lowerleft); and Wild Turkey(Meleagris gallopwoo; lower right). Scale under each wing is in inches(upper) and cm (lower). ducer.Use of a waterflow tunnelprovides high res- ficient remains stable and constant across Re values olutionof lift and dragforces, which, as long asthe of 5 x lip to 5 x l0 s (Vogel 1983). Reynoldsnumber is similar(see below), gives useful Forceswere measured separately with a strain-gauge datafor lift anddrag coefficients. Water speed in the transducer(sensitivity 2 x 10-3 N) as one arm of a flow tunnel was 0.5 m/s.

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