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rows, Zonotrichiaalbicollis. Anim. Behav. 40: 116- singing conspecificsby the Carolina Wren. Auk 181. 98:127-133. HURLY, T. A., L. RATCLIFFE, D. M. WEARY, AND R. Srr~crunro~, S. A. 1991. Singing behaviour of WEISMAN. In press. White-throated Sparrows Black-capped Chickadees (Purus atricapillus). (Zonotrichia albicollis) can perceive pitch change M.Sc.thesis, Queen’s University, Kingston, On- using frequency ratio independent of frequency tario, Canada. difference. J. Comp. Psych. WEARY, D. M., R. G. WEISMAN, R. E. LEMON, T. CHIN, MARLER, P. 1960. songsand mate selection, p. AND J. MONGRAIN. 1991. Use of the relative fre- 348-367. In W. E. Lanyon and W. N. Tavolga quencyof notesby Veeries in songrecognition and teds.], soundsand communication. Amer- production. Auk 108:977-98 1. ican Institute of Biological Sciences,Washington, kk&A~, R., ANDL. RAT-. 1989. Absolute and DC. relative pitch processingin Black-capped Chick- NELSON, D. A. 1989. The importance of invariant adees, Parus atricapillus. Anim. Behav. 38:685- and distinctive features in speciesrecognition of 692. bird song. Condor 9 1:120- 130. WEISMAN, R., L. RATCLIFFE,I. JOHNSRUDE,AND T. A. RICE.W. R. 1989. Analvzina tablesof statisticaltests. HURLY. 1990. Absolute and relative pitch pro- Evolution 43:223-225. - duction in the song of the Black-capped Chicka- RICHARDS,D. G. 1981. Estimation of distance of dee. Condor 92: 118-124.

The Condor945 ’85481 0 TheCooper Ornithological society I992

SONGS OF TWO MEXICAN POPULATIONS OF THE WESTERN FLYCATCHER DZFFZCZLZS COMPLEX’

!!?IEVEN. G. HOWELL Point ReyesBird Observatory,4900 ShorelineHighway, Stinson Beach, CA 94970

RICHARD J. CANNINGS Cowan VertebrateMuseum, Department of Zoology, Universityof British Columbia, 6270 UniversityBoulevard, Vancouver,British Columbia V6T 124, Canada

Key words: Song;Mexico; WesternFlycatcher; Pa- they are described here to contribute to our under- ctfic-slopeFlycatcher; Cordilleran Flycatcher: Empi- standingof this interestingcomplex. Vocalizationswere donax difficilis; Empidonax occidentalis. recordedon a Sony TCS 430/450 cassette-recorderus- ing a Radio ShackElectret tie-pin microphone mount- Johnson (1980) provided a detailed treatment of the ed in a plastic funnel, and analyzed on a Ray 7029A Western Flycatcher(Empidonax dtjicilis) complex, and sound spectrum analyzer. As in Johnson (1980), mea- more recently Johnson and Marten (1988) recom- surementswere made from the singleclearest recording mended that coastal and interior populations of E. from each bird. Although our sample sizes are very dijicilis be consideredspecifically distinct. This course low, advertising songsin the E. dt$iciliscomplex tend was followed by the American Ornithologists’ Union to be similar over broad geographic areas (Johnson (1989) naming coastalbirds the Pacific-slopeFlycatch- 1980), so recordingsof singlebirds can be quite mean- er (E. d@cilis) and interior the Cordilleran Fly- ingful in a study of geographicvariation. catcher (E. occidentalis).Johnson ’s (1980) analysis of E. d. cineritius:this bird is common in the fairly arid vocalizationslacked the advertising songsfrom several - forests of the Sierra Iaguna (= Sierra Vic- key areas,and included none from Mexico. Recordings toria), southern Baja California. Two singing individ- from two areas would be of particular interest: (1) in- uals were tape-recorded at the northern end of La La- terior-breeding birds in Mexico, which Johnson(1980) guna meadow on 9 and 10 June 199 1; representative suggestedmight not have a complete advertising song; songsfrom each individual are shown in Figure 1 (A and (2) the distinct population (E. d. cineritius)in the and B). In the field, the songsclearly recalled those of Cape District mountains of southern Baja California birds in coastal California. but thev are lower Ditched which was given “megasubspecies”status by Johnson (cf. Johnson 1980:fig. 28, Santa Barbara sample), par- (1980). ticularly syllable 1 (Table 1). Also, the peak of syllable During recentfield work, one ofus (Howell) recorded 2 is not asacute as in typical coastalsongs, being similar the advertising songsof birds from both these areas; in this respect to songs from the California Channel Islands population. Channel Islands birds also tend to have low pitched songs, although not as low as the Sierra Lagunabirds (Table 1). Syllable 3 is clearly typ- 1Received 24 March 1992. Accepted 20 April 1992. ical of coastal populations (Johnson 1980:fig. 26). 186 SHORT COMMUNICATIONS

a syllable 1 Syllable 2 Syllable 3 A

6

4 . f

2 -

’ ’ 1 2 B

$ 6,

1‘ 2 1 Time kecm3d FIGURE 1. Sound spectrographsof advertising songsof Western Flycatchers in Mexico. A and B: Pacific- slope Flycatchers, Sierra Laguna, Baja California Sur; C: Cordilleran Flycatcher, Tlanchinol, Hidalgo.

Morphologically, Johnson (1980) found E. d. cineri- on 9 June 1990 in humid evergreenforest (cloud forest) tius to be clearly allied to other coastal populations, at 1,500 m elevation, 5 km N of Tlanchinol, in the grouping close to the populations from Sierra San Pe- northern part of the state of Hidalgo. Cordilleran Fly- dro Martir (northern Baja California) and the Channel catcherswere common there and at least one other was Islands; its song supports this relationship. The male heard singing. Howell also heard several singing Cor- position notes recordedfrom Sierra Laguna(Fig. 2) are dilleran Flycatchersin the of similar to those of mainland coastalpopulations rather Chihuahua in mid-July 1991 and noted that their song than the simplified calls of Channel Islands birds recalledthat of the Hidalgo birds and birds in southern (Johnson 1980:fig. 29). Arizona. Measurements taken from the songin Figure E. occidentalis:the song in Figure 1C was recorded 1C are similar to those of songsrecorded by Johnson

TABLE 1. Measurements of advertising songs of Western Flycatchers in Mexico and southwesternUnited States.’

Mean frequency Frequencyspread Frequencyspread Mean frequency syllableI part 2, syllable2 part 3, syllable2 syllable3

Sierra Laguna A 4.709 4.589 2.913 4.621 Sierra Laguna B 4.469 4.342 2.123 4.565 Santa Barbara2 5.960 4.000 2.300 5.320 Channel Islands* 5.282 3.964 2.036 4.900 Tlanchinol, Hidalgo 5.523 1.437 0.583 4.070 SE Arizona2 5.614 2.086 0.843 4.129 ’ ’ Measurementsbased on Johnson’s(1980) Table 2, all in kilohertz.Measurements of Mexicansongs based on one songfrom eachindividual. 2Population mean from Johnson(198O:Eg. 28). SHORT COMMUNICATIONS 181

type to those 1,200 km to the north in the interior southernUnited States,and their advertisingsongs show little gradationtoward the songsgiven by the Yellowish Flycatcher (E. jluvescens,Johnson 1980:fig. 27), a sib- ling speciesbreeding as closeas 500 km to the Hidalgo site. Recordings of advertising songs of Cordilleran Flycatchersfrom Oaxaca and of Yellowish Flycatchers from southeasternVeracruz or southeasternOaxaca, i.e., where these ’ rangesapproach most closely, would further clarify this situation (Johnson’s north- ernmost recordingsof the latter speciescame from Nic- aragua). We thank N. K. Johnson for comments on a draft of this paper. This is contribution number 534 of Point Reyes Bird Observatory.

I LITERATURE CITED 1 0.5 AMEIUCANORNITHOLOGISTS UNION.’ 1989. Thirty- seventh supplement to the American Omitholo- Time (seconfis) gists’ Union check-list of North American Birds. Auk 106:532-538. FIGURE 2. Soundspectrograph of male position note JOHNSON,N. K. 1980. Character variation and evo- of Pacific-slope Flycatcher from Sierra Laguna, Baja lution of sibling speciesin the Empidonax dz$- California Sur. cilis-jlavescenscomplex. Univ. Calif. Pub. Zool. 112:1-151. (1980) in southeasternArizona (Table l), although the JOHNSON,N. K., ANDJ. MARTEN. 1988. Evolutionary frequency spread of the descendingportion (part 2) of genetics of flycatchers. II. Differentiation in the syllable 2 is much narrower. Thus, Cordilleran Fly- Empidonax di&icilis‘ complex. Auk 105:177-191. catchersin southernMexico seemclosely allied by song-

The Condor94:X37-190 0 The Gxwr OrnithologicalSociety 1992

THE INFLUENCE OF GROUP SIZE ON VIGILANCE IN CAPTIVE-RAISED RING-NECKED PHEASANTS ’

BARRYN. MILLIGAN? Department of Biology, Universityof Regina, Regina, SaskatchewanS4S 0A2, Canada R. MARK BRIGHAM Department of Biology, Universityof Regina, Regina, SaskatchewanS4S 0A2, Canada

Key words: Behavior; focal analysis; foraging; (e.g., information-transfer; Ward and Zahavi 1973), groups:Phasianus colchicus; Saskatchewan; ring-necked minimize the risk of predation through dilution (Ham- pheasants;vigilance. ilton 1971), or increase group vigilance (Abramson 1979). These ideas have been usedto explain the func- Two of the main environmental influenceson the evo- tion of groups in many different , e.g., com- lution of animal aggregationsare thought to be food munal roostsofbirds (Weatherhead 1983), fish schools availability and predation pressure (Bertram 1980). (Brown and Downhower 1988), and maternity colonies Group formation is hypothesized to be a means by of bats (Kunz 1982). which individuals can exploit uneven food supplies Evaluating the function of aggregationsshould pro- vide insight into the degree of food availability and predation pressure to which an animal is subjected. For example, Bertram (1980) showed that although I Received 16 January 1992. Accepted28 April 1992. individual Ostriches(Struthio camelus)spent lesstime 2 Present address: Department of Biology, Univer- scanningwhen in groups,overall vigilance (proportion sity of Victoria, P.O. Box 1700, Victoria, British Co- of time when at least one bird scanned)increased with lumbia V8W 2Y2, Canada. group size. If, by being in larger groups, individual