Although presence or absence of scutes on the legs of passerine birds has been widely noted (e.g., Rand, 1959; Dorst, 1960), scutes on the feet have been generally neglected. Recent studies on oscincs (Clark, 1972, 1974) revealed that foot-scutcs often vary taxonomi- cally, and the goal of this report is to summarize new data on 222 species from Canada and the U.S. Such information potentially contributes to adaptive and systematic analyses (Clark, 1974) and can aid, together with foot size and color, in identifying the iso- lated feet sometimes found among the remains of prey. I studied the large scutes on the acropodium and distal end of the acrotarsium because (1) in some families they vary relatively little intraspecifically (Clark, 1972), and (2) adequate samples of study skin specimens were available. Sufficient numbers of em- balmed or frozen specimens have not been available to enable equivalent studies on other surfaces of the feet, but Blaszyk (1935), Staaland (1964), Clark (1972, 1973), Lennerstcdt (1974, 1975 a,b,c) and Lcisler (1975) have discussed these body regions for oscines, mainly from Europe. MATERIALS AND METHODS I examined more than 8,000 study skins, plus some embalmed specimens and wild birds captured for banding. Table i lists the genera studied. Although the described features are usually visible with a hand lens, I often used a dissecting microscope. Reference to statistically significant differences indicates a probability of less than 0.01 in a Chi-square test. SCUTES OF THE ACROPODIUM AND DISTAL ACROTARSIUM To compare foot-scutes I first describe those of the Rufous- sided Towhee (Pipilo erythrophthalmus), a species chosen for its relatively large size, low intraspecific variation, and wide North American distribution. A new terminology enables a concise pre- sentation of data on foot-scutes. At the distal end of the acrotarsium lie five transversely elongated scutes, termed A through E from proximal to distal (Fig. 1). Scute A is typically larger than B. Scute C, often a useful landmark, medially meets a proximo-distally elongated scute X. Scute D medially contacts the most proximal scute of a row along the inner toe (II). Scute E, an important landmark, lies at the proximal end of the middle (III) and outer (IV) toes. TABLE 1. Genera examined with number of species if more than one per genus Alaudidac: Eremophila; Hirundinidac: Tachycineta, Iridoprocne, Riparia, Stel- gidopteryx, Hirundo, Petrochelidon, Progne; Corvidae: Perisoreus, Cyanocitta (2), Aphelocoma (2), Cyanocorax, Pica (2), Corvus (4), Gymnorhinus, Nucifraga; Paridac: Parus (7), Auriparus, Psaltriparus; Siftidac: Sitta (4); Ccrthiidac: Certhia ; Chamacidac' Chamaea ; Cinclidac: Cinclus ; Troglodytidac: Troglodytes (3), Thryomanes, Thryothorus, Campylorhynchus, Cistothorus (2), Catherpes, Salpinctes ; Mimidae: M imus, Dumetella, Toxostoma (5), Oreoscoptes ; Turdidae: Turdus, Ixoreus, Hylocichla, Catharus (4), Sialia (3), Myadestes; Sylviidac: Polioptila (2), Regulus (2); Motacillidac: Anthus; Bombycillidac: Bombycilla; Ptilogonatidac: Phainopepla; Laniidac: Laius (2); Sturnidae: Sturnus; Vire- onidae: Vireo (8); Parulidae: Mniotilta, Protonotaria, Limnothylpis, Helmitheros, Vermivora (7), Parla (2), Peucedramus, Dendroica (18), Seiurus (3), Oporornis (4), Geothlypis (2), Icteria, Euthlypis, Cardellina, Wilsonia (3), Setophaga, Myio- bors; Ploccidac: Passer; Ictcridae: Dolichonyx, Sturnella (2), Xanthocephalus, Agelaius (2), Icterus (6), Euphagus (2), Quiscalus (3), Molothrus (2); Thraupidac: P iranga (4); Cardinalinac: Cardinalis (2), Pheucticus (2), Guiraca, P asserina (4), Spiza ; Carduclinae: Hesperiphona, Carpodacus (3), Pinicola, Lecosticte, Car- duelis (5), Loxia (2); Embcrizinac: Arremonops, Pipilo (4), Calamospiza, Pas- serculus, Ammodramus (2), Ammospiza (2), Pooecetes, Chondestes, Aimophila (5), Amphispiza (2), Junco (3), Spizella (6), Zonotrichia (4), Passerella, Melo- spiza (3), Calcarius (3), Plectrophenax. Along toe II, scute counts begin immediately distal to C, whereas counts on toes III and IV start immediately distal to E. The Rufous-sided Towhee typically has 9 scutes on toe II, 10 on III, and 8 on IV (Fig. 2). Scutes termed caps (stippled in Figs. I and 2) lie near the joints of the toes and are major landmarks. The proxi- real cap of toe III is an especially useful landmark, ordinarily separated by one scute from E. I initially found great individual variation in counts on the hallux (toe I) and hence did not study that toe further. INDIVIDUAL AND TAXONOMIC VARIANTS All species exhibit individual variation and some are highly variable; hence I routinely examined at least six specimens, and often many more, for each species. The same kinds of variation can occur either intraspecifically or interspecifically, depending on B I 2turn I FZGURE 1. Dorsal view of the foot of a Rufous-sidcd Towhec (Pipilo erythro- phthalmus). Caps are indicated by stippling. See text for details. the particular taxonomic groups. For example, scutc E is commonly either divided or intact, i.c., varied, in Cardinals (Cardinalis cardinalis) but is typically intact in Rufous-sidcd Towhoes and typically divided in Rose-breasted Grosbeaks (Pheucticus ludo- vicianus) . Variants include divisions of scutcs C, D, or E, all of which often occur in certain thrushes (Turdidac; Fig. 3). C, D, and E are termed varied when they are commonly either intact or divided within a taxon, as is scutc E in Cardinals. The number of scutcs per toe is designated by the Roman nu- meral of that toe followed by a hyphen and the count, c.g., IV-9 signifies nine scutcs on the outer toe. Variation in number of scutcs per toe within a taxon is designated by listing common variants separated by commas, c.g., "11-7, 8, 9" indicates that 7, 8, or 9 scutcs occur commonly on the inner toe. In certain taxa, c.g., all wrens (Troglodytidac), two narrow contiguous scutes occur in the region of the proximal cap on toe IV (Clark, 1974: Fig. 1); this condition is recorded as "ds" (double scutc). Other differences in number of scutcs on particular sections of a toe can be specified by the number proximal or distal to particular caps. For conciseness, I have usually listed neither uncommon variants nor frequencies of common variants. My intent is to describe representative individuals and not the full range of variation for each taxon. For certain taxa, structural differences limit the use of the descriptive system based on the Rufous-sidcd Towhoe. Moreover, for certain families, great individual variation in the A to E region precludes concise description. Furthermore, xvhcrc equivalents for scutes C and E were uncertain, I could not count scutes on toes II and IV, because these counts require unambiguous recognition of C and E. Scutcs on toe III could still be counted with the proximal cap as a landmark. Where equivalence of scutes in the A to E region is uncertain, I have for conciseness, without implying hornology, designated the scutc at the base of the two outer toes as E. TAXONOMIC COMPARISONS Larks (Alaudidae), swallows (Hirundinidac), corvids (Corvidac), titmice (Paridac), nuthatches (Sittidac), creepers (Ccrthiidac), and vireos (Virconidae) differ in the A to E region in varied ways so greatly from Pipilo that the descriptive code is often not easily applied. Swallows often appear to have one less row of transverse scutcs than the five (A through E) in Pipilo, whereas some corvids, some nuthatches, and creepers often have an extra scutc row relative to Pipilo. Larks, swallows, corvids, titmice, nuthatches, creepers, and vireos all have a divided E, except for the varied E in some Verdins (Auriparus; Clark, 1974). All these families except Virconidac have a conventional proximal cap on toe III, thus enabling the following scute counts for that toe: Alaudidae, III-8; Hirundinidac, 111-9, 10; Corvidac, III-9 to 12 (often 10 or 11, but sometimes 9 in Corvus and usually 11 or 12 in Perisoreus); Paridae, D E I ! 2mm FGURE 2. Lateral view of toe IV of a Rufous-sided Towhee. Caps are indicated by stippling. x A B CD E I I FIGURE 3. Dorsal view of the A to E region of a Hermit Thrush (Cathams guttara). Note divided scutes C, D, and E. 111-9, 10; Siftidac, III-10, 11, but typically 12 in the White-breasted Nuthatch (Sitta carolinensis); Certhiidae, III-11, 12. Vireos are unusual in typically lacking a conventional cap in the proximal position on toe III. For other North American families and subfamilies, Table 2 summarizes many findings in a generalized way, and additional details follow. TAB.E 2. Generalized summary of foot-scute variations. Seute Scutes per toe Taxon C D E II III IV ds Chamaeidae i v d 9 9,10 9 a Cinclidae v v d 11 10,11 9 p Troglodytidae i v d 8 to l0 ll 9,10 p Mimidae i,v i,v i,d l0 ll 9 to ll p Turdidae v v d 9 to ll 10,11 9 to ll p Sylviidae i,d v,d d 8,9 l0 8,9 a Motacillidae d v d 9 11 8,9 a Bombycillidae d v d 9, l0 10, I 1 9 a Ptilogonatidae v a i 9 10 8,9 a Laniidae v v d 9 l0 8 a Sturnidae i i d 10,11 I 1 l0 p Parulidae i,d i,d i,d 9 10,11 8,9 a Ploceidae v v d 9 l0 8 a Icteridae v v d 9 l0 8,9 a Thraupidae v v d 9 l0 8,9 a Cardinalinae i,v v d 9 l0 8,9 a Carduelinae d v d 7 to 9 9,10 7 to 9 a Emberizinae i,v,d i,v i,d 8,9 9,10 8,9 a Abbreviations: i, intact; v, varied; d, divided; a, absent; p, present. Troglodytidae.--Wrens, other than Catherpes and Salpinctes, are unusual in typically lacking a conventional cap on toe II and in the distal position on toe IV. Mimidae.--Most North American mimid species have intact C, D, and E. However, the Gray Catbird (Durnetella carolinensis) varies in C and D and has a divided E (Clark, 1972: Fig. 2). Among the mimids, the Gray Catbird and Curve-billed Thrasher (Toxos- torna curvirostre) are exceptional in frequently having IV-11 as well as IV-9, 10. Turdidae.--In thrushes, the count for III is often 11, except for III-10 in the Gray-cheeked Thrush (Catharus minimus) and III-10, 11 in bluebirds (Sialia). C. rainlinus thus differs notably from the three other Catharus species. Sylviidae.--Polioptila usually has an intact C with a varied D, and Regulus commonly has both C and D divided. Both genera typically have a divided E and lack a ds. In Polioptila a conventional cap is often absent on II, with II-8. Regulus typically has II-9. Among these four species only the Golden-crowned Kinglet (R. satrapa) typically has IV-9 (Clark, 1974). Parulidae.--C is usually intact but often divided in Mniotilta, and relatively varied in Protonotaria, Dendroica caerulescens, D. fusca, and Myioborus picta. D is usually intact, but divided in Peucedravus (Clark, 1974) and varied in Mniotilta. In most species E is divided, but the Yellow-breasted Chat (Icteria virens) is exceptional with an intact E (Clark, 1974). In parulids the count for toe II is usually 9 but sometimes 8. Toe III usually has 10 scutes, but is especially varied in Seiurus (Table 3), often has 11 in Peucedrarnus, and typically 11 in Icteria (see also Clark, 1974). Seiurus illustrates the occurrence of statistically significant dif- ferences between each of three congeners. In parulids the IV count is usually 8, but sometimes 9, and is typically 9 in Peucedranus. TABLE 3. Number of individuals with two (typically III~9) versus three (typically III~10) small scutes adjacent to the claw of toe III in Seiurus Number of scutes Species 2 3 S. aurocapillus 73 16 S. noveboracensis 55 34 S. motacilla 12 18 Icteridae.--Usually the IV count is 9, but 8 is more common in Sturnella (Clark, 1974). Cardinalinae.--C is usually intact except in Pheucticus and Spiza, in which C is varied. E is typically divided though many Cardinals have an intact E (Clark, 1974). Carduelinae.--In Carpodacus counts for toe IV differ signifi- cantly between all three species (Table 4); the Purple Finch (C. purpureus) differs from other carduelines in having a majority of individuals with IV-9. The Redpoll (Carduelis fiamvea) has rela- tive!y low counts of II-7, 8, 9; III-9, and IV-7, 8. Redpolls often lack a conventional cap at the distal position on toe IV. Emberizinae.--In all except Calcarius and Plectrophenax, C, D, and E are typically intact (see also Clark, 1972, on E) with II-9, III-10, IV-8, but exceptions are (1) a high frequency of IV-9 in Abert's Towhee (Pipilo aberti; Clark, 1974), (2) II-8 and III-9 as typical for Grasshopper Sparrows (Avvodravus savannarum), (3) III-9, 10 for Sharp-tailed Sparrows (Amvospiza caudacuta) and (4) the divided C of Fox Sparrows (Passerella iliaca; Clark, 1974: Fig. 3). T.BLr 4. Number of individuals with three (typically IV-8) versus four (typically IV-9) scutes distal to the most distal cap on toe IV in Carpodacus Number of scutes Species 3 4 C. purpureus 7 38 C. cassinii 32 13 C. mexicaus 60 6 In Calcarius and Plectrophenax C and D are varied, although C is frequently intact; they also have a divided E, II-8 or 9, III-9, and IV-8. DISCUSSION Despite individual variation in foot-scutes within each species, many taxonomic differences are detectable among the oscines. However, the overall range of variation is limited, e.g., in scute counts along the toes (Table 2), and overlap can occur between taxa that are probably not closely related taxonomically, e.g., Bombycillidae and Carduelinae. Hence caution is necessary in using foot-scutes for systematic or identification purposes. The new data presented here should provide an improved basis for future studies analyzing adaptations of the feet and comparing North American oscines with those from other geographic areas. SUMMARY Foot-scutes of the Rufous-sided Towhee (Pipilo erythrophthalmus) are compared with those of 221 other species of North American oscines. New examples of differences between congeneric species involve the genera Catharus, Seiurus, Carpodacus, and Carduelis. ACKNOWLEDGMENTS J. E. Ahlquist (Yale Peabody Museum), S. M. Russell (Uni- versity of Arizona), and G. E. Watson (National Museum of Natural History, Washington, D.C.) generously provided access to specimens. Aid was also given by G. T. Austin, E. L. Smith, S. Speich, and R. L. Zusi. Jonathan R. Craig prepared the illustra- tions. P. Brodkorb, J. A. Slater, and an anonymous reviewer pro- vided helpful suggestions concerning the manuscript. LITERATURE CITED B,,szY, P. 1935. Untersuchungen fiber die Stammesgeschichte der Vogel- schuppen und Federn und fiber die Abhangigkeit ihrer Ausbildung am Vogelfuss von der Funktion. Gegenbauer's Morph. Jahrb., 75:483-567. CLARX, G. A., JR. 1972. Passerine foot-scutes. Auk, 89:549-558. 1973. Notched toe pads in climbing oscines. Condor, 75:119-120. ---. 1974. Foot-scute differences among certain North American oscines. Wilson Bull., 85:104-109. DORS% J. 1960. Les caracteres de la scutellation du tarse chez les vangides- Oiseau, ${):32-41. LEISLER, B. 1975. Die Bedeutung der Fussmorphologie far die 6kologische Sonderung mitteleuropaischer R6hrsanger (Acrocephalus) und Schwirle (Locustella). J. Ornithol., 116:117-153. LEERSTDT, I. 1974. Pads and papillae on the feet of nine passerine species. Ornis Scand., 5:103-111. ß 1975a. Seasonal variation in foot papillae of Wood Pigeon, Pheasant and House Sparrow. Comp. Biochem. Physiol., 51A:511-520. ß 1975b. Pattern of pads and folds in he foot of European oscines (Aves, Passeriformes). Zoologica Scripta, 4:101-109. ß 1975c. A functional study of papillae and pads in the foot of passerines, parrots, and owls. Zoologica Scripta, 4:111-123. RAN), A. L. 1959. Tarsal scutellation of song birds as a taxonomic character. Wilson Bull., 71:274-277. STAALAND, H. 1964. Variation in passerine foot-sole structures and its relation to ecological differences. Nytt Magasin for Zoologi, 12:48-64. Biological Sciences Group, University of Connecticut, Storrs, Con- necticut 06268. Received 10 July 1976, accepted 3 June 1977.