762 SHORT COMMUNICATIONS creased protection of existing sites will become even Hov~s, J. A., AND M. S. ROBSON. 1989. Breeding more imnortant. status and distribution of the Least Tern in the Florida Keys. Fla. Field Nat. 17:61-66. We thank C. Chase. C. Harbison. P. Hutto. A. In- JACKSON,J. A., AND B. J. JACKSON. 1985. Status, gram, R. Ingram, H. Gftin, G. Lyman, T. Mehart, R. dispersion, and population changesof the Least Renken, H. Smith, R. Smith, and J. Vickers for their Tern in coastal Mississippi. Colonial Waterbirds careful observations of tern nests. H. Loftin helped 8:54-62. organize observers and C. Chase and H. Smith gave JOHNSON,D. H., ANDT. L. SHAFFER.1990. Estimat- useful advice. C. Collins, J. Jackson, B. Massey, B. ing nest success:when Mayfield wins. Auk 107: Millsap, and T. O’Meara provided helpful comments 595-600. on the manuscript. We also thank the property owners KOTLIAR,N. B., AND J. BURGER. 1986. Colony site and managers who kindly permitted us accessto the seletion and abandonment by Least Terns (Sterna study sites. antillarum) in New Jersey, USA. Biol. Conserv. LITERATURE CITED 37:1-21. MAYFIELD,H. 196 1. Nesting successcalculated from ATWOOD,J. L., ANDB. W. MASSY. 1988. Site fidelity exposure. Wilson Bull. 73:255-26 1. of Least Terns in California. Condor 90:389-394. MASSEY,B. W., AND J. L. ATWOOD. 1981. Second- BURGER,J. 1984. Colony stability in Least Terns. wave nesting of the California Least Tern: age Condor 86:61-67. composition and reproductive success.Auk 98: BURGER,J., AND M. GCXHFELD. 1990. Nest site se- 596-605. lection in Least Terns (Sterna antillarum) in New MASSEY,B. W., ANDJ. M. FANCHER.1989. Renesting Jerseyand New York. Colonial Waterbirds 13:3l- bv California Least Terns. J. Field Omithol. 60: 40. 350-357. FISK, E. J. 1975. Least Tern: beleaguered,opportu- THOMPSON,S. M. 1979. Relative reproductive suc- nistic, and roof-nesting. Am. Birds 29: 15-16. cessat LeastTern coloniesin the Charleston,South FISK. E. J. 1978. Roof-nesting terns. skimmers. and Carolina area. Unpublished grant completion re- plovers in Florida. Fla. Field Nat. 6:1-8. ’ port, Nat. Audubon Sot., New York. GOODNIGHT,L. E. 1957. Least Tern. Fla. Nat. 30: 123.

The Condor 93:162-X5 0 The Cooper Ornithological Society 1991

BREEDING DISTRIBUTION AND HABITAT OF PRAIRIE FALCONS IN NORTHERN MEXICO ’

DIRK V. LANNING 353 N. W. ClevelandSt., Pullman, WA 99163-3101 MARK A. HITCHC~CK 21 I Rio Vista Circle. San Angelo, TX 76904

Key words: Prairie Falcon; Falco mexicanus;Mex- Prairie Falcon nest sites, and collected limited data on ico; distribution;breeding; habitat. their occupancy, productivity, and habitat during a study of PeregrineFalcons (Falco peregrinus)in north- The Prairie Falcon (Falco mexicanus)breeds in Can- em Mexico between 1975 and 1986. ada and the United States (US) south to Baja Califor- nia, southernArizona, southernNew Mexico, western STUDY AREA AND METHODS Texas, and southeasternCoahuila (AOU 1983). C. A. The study area (Fig. 1) included the mountains of Ely (1962) collected one of two immature Prairie Fal- northern Mexico, known as the Sierra Madre Occi- cons on 30 June 1958 at a nest cliff in the mountains dental in northwestern Mexico and the Sierra Madre of southeasternCoahuila; this is the only published Oriental in northeastern Mexico. Sheer cliffs are com- nesting record we are aware of for Mexico outside of mon in the mountains and canyons.Cliffs in the north- Baja California. We observed Prairie Falcons, located west are of mostly igneousorigin, thosein the northeast are usuallylimestone. The climate varies with altitude and with proximity to the moist coastal regions or I Received 30 October 1990. Final acceptance3 April interior arid desert. Spring and summer temperatures 1991. generallyrange from lO-30°C in the mountains. Mean SHORT COMMUNICATIONS 763

FIGURE 1. Map of northern Mexico, showingthe locationsof 23 Prairie Falcon sitesin the statesof Chihuahua, Coahuila, Durango, and San Luis Potosi.

annual precipitation varies from 30-60 cm and from maps and photographs.We usedropes of known length 55-82% falls from June throuah Seotember (Institute to measure the height of several nests and cliffs. We de Geografia 1970). - _ . used topographic, aeronautic, climate, and vegetation Five major biotic communities occur in the moun- maps produced by the Mexican government. tains (Brown 1982). Madrean Montane Conifer Forest, We determined occupancyand productivity during dominated by pines (Pinus spp.) and other conifers, at least one breeding seasonat each nest site. We were and Madrean Evergreen Woodland, dominated by a able to return to only a few of the easily accessiblesites variety of larger oaks (Quercus spp.), are prominent for observationsin two or more breeding seasons.We above 2,000 m elevation. Interior Chaparral occurs usually made one visit to each site, lasting only one or below 3,000 m and consistsof low-growing oaks and two days, and may have inaccurately listed a known a variety of other shrubsand compact trees. Semidesert site as unoccupiedwhen the site may have been occu- Grassland, with numerous grasses,shrubs, and suc- pied at another period during the same breeding sea- culents,is common in the int&montane valleys betwen son; Allen (1987b) discussesthis bias in Prairie Falcon 2,000 and 2.500 m. Chihuahuan Desert scrub. com- surveys.In most caseswe recorded only the minimum mon below 2,000 m on the lower slopesof the moun- number of youngvisible and audible;more youngmight tains and in the valleys and canyons,is dominated by have been present, but were not visible. At sites where creosotebush (Larrea tridentata), tarbush (Fluorensia all fledgedyoung were visible and the entire nest floor cernua),and whitethorn acacia(Acacia neovaernicosa). was visible, we recorded the exact size of the brood. W. G. Hunt and M. A. Hitchcock began the search Results for each site and each pair during a breeding for Peregrine Falcons in northeastern Mexico during seasonare listed as site-year and pair-year, respective- the breeding seasonof 1975 (Hunt 1976). The Pere- ly. grine Falcon study continued throughout northern Mexico during 1976, 1977, 1978, 1979, and 1982 (Hitchcock 1978, Lanning et al. 1985, Hunt et al. 1988) RESULTS and during 1986 (Lanning and Jenkins, unpubl.). We Between 1975 and 1986 we visited 23 Prairie Falcon recorded incidental observations of Prairie Falcons sites in northern Mexico: 11 in Chihuahua, 6 in Coa- during the Peregrine Falcon research. huila, 5 in Durango, and 1 in San Luis Potosi (Fig. 1). We surveyed potential Prairie Falcon nesting sites We observedincubation behavior as early as 13 March by observingcliffs in the early morning and in the late and as late as 30 April, pairs with nestlings between afternoon and early evening, when falcons were likely 21 April and 7 June, and fledglings between 20 May to be active and vocal. The term “nest site” includes and 23 June. the nest and its nearby surroundings,such as the cliff We collected occupancyand productivity data dur- or set of cliffs occupied by the falcons. We searched ing one breeding seasonat 12 sites and during two or cliffs at least 25 m tall and at elevations above 1,500 more breeding seasonsat 11 sites. Occupancyby Prai- m. At each nest site, we measuredthe cliff used during rie Falcons was determined for 49 site-years. The site the latest year that young were produced. If no young occupancyrate was 84%. Pairs were observed during were known from a site, we used the cliff most recently 38 (78%) ofthe site-years.Single falcons were observed occupied by a pair. We estimated cliff rim elevation, during three site-years(6%) and cliffs were unoccupied cliff height, cliff length, cliff orientation, and percent for eight site-years (16%). We determined minimum coverage for the biotic communities with the aid of productivity for 28 pair-years. At least one nestling or 764 SHORT COMMUNICATIONS

fledgling was produced during 27 pair-years. We ob- North America; it also breeds less commonly in tim- tained exact acountsof only six fledged broods, which bered mountains up to 3,700 m (Cade 1982). The hab- contained 2, 3, 3, 3, 3, and 4 young (K = 3.0 + 0.63 itat for the Prairie Falcon in northern Mexico is a com- WA). bination of forest, woodland, and chaparral in the Cliff rim elevations of the 23 sites were from 1,600 mountainous terrain surrounding the nest site and to 3,200 m (K = 2,450 + 370). The 23 cliffs were 25 grasslandand desert scrub on the open slopesand val- to 130 m tall (x = 65 + 35) and 40 to 1,000 m long leys, often in front of and below the nest site. (K = 350 f 270). Cliffs faced north (2), northeast (2), Our search for Prairie Falcon sites was not exhaus- east (3), south (4) southwest (4), and west (8). Nests tive and was conducted in the mountains. Prairie Fal- at seven measured cliffs were from 6 to 30 m (x = 15 cons probably nest at lower elevations in northern + 7) below the top of the cliff and between 10 and 90 Mexico on cliffs that are completely surrounded by m (x = 35 + 30) above the base of the cliff; mean nest grasslandand desert scrub.Further researchin Mexico height was 65% (? 14) of cliff height. The forest, wood- is needed to locate breeding Pairie Falcons south of land. and chanarral biotic communities of the moun- our studv area. tams covered‘10 to 80% (x = 60 IfI 25) of the terrain We thank the many observersin the Peregrine Fal- within a 15-km radius of each of the 23 cliffs. The con study for their Prairie Falcon observations. We grasslandand desert scrub biotic communities of the sincerely appreciate Grainger Hunt’s enthusiasm, en- open slopes and valleys covered the remaining 20 to couragement,and advice; the Peregrine Falcon study 90% yz = 40 f 15). in Mexico might never have been initiated without his DISCUSSION leadership.Logistical and financial supportfor the Per- egrine Falcon study was provided by the Chihuahuan Our observations of the breeding Prairie Falcons in Desert Research Institute, G. M. Sutton Avian Re- Chihuahua. Coahuila. Duranao. and San Luis Potosi search Center, National Audubon Society, National have expanded upon’the sin& record of Ely (1962) EcologyResearch Center of the U.S. Fish and Wildlife and the 1983 AOU summary for northern Mexico. Service (USFWS), National Geographic Society, and Two nest sites in Coahuila were within 2 km of the the United States-Mexico Joint Committee on Wildlife nest described by Ely (1962). We found nest sites as Conservation of the USFWS and the Direcci6n Gene- far south as 23”30’N latitude. However, there is no ral de Flora Y Fauna Silvestres. Mike Boaan. David reason to assumethis was the southernlimit of breed- Ellis, Alan Jenkins, Peter Lawson, John Gldkmeyer, ing in Mexico. Richard Porter, and Jim Sedgwickcritiqued the Prairie Prairie Falcon sites in northern Mexico had an 84% Falcon information as part of a larger unpublished occupancy rate, similar to Prairie Falcons in the US manuscript. This short communication has been re- Rocky Mountain Region, where an average of 27 (x = viewed by George Allen, Noel Snyder, Susan Tom- 87%) out of 31 sites were occupied over a three-year quist, and an anonymousreviewer. To all of the people period (Enderson 1964). In northern Mexico there was and organizationswho directly and indirectly helped, an average of 3.0 fledged young from six successful we give our deepest appreciation. nests. Ogden and Homocker (1977) found a mean of 3.7 fledgedyoung per successfulnest (9 1 nests)and 3.1 LITERATURE CITED fledgedyoung per nestingattempt (110 nests)in south- western Idaho. Olendorff and Stoddart (1974) reported ALLEN, G. T. 1987a. Prairie Falcon aerie site char- a mean of 3.4 fledged young per nesting attempt (27 acteristicsand aerie use in North Dakota. Condor nests)in northeasternColorado. Enderson(1964) found 89:187-190. a mean of 1.4 fledged young per nesting‘ attempt (67 ALLEN, G. T. 1987b. Estimating Prairie Falcon and pairs that laid eggs) and 1.2 fledged young per pair Golden Eagle nesting populations in North Da- studied (77 pairs). kota. J. Wildl. Manage. 5 1:739-744. Prairie Falcon nest cliffs in northern Mexico were AME~UCANORNITHOLOGISTS' UNION. 1983. Checklist similar to nest cliffs in the US. Runde and Anderson of North American birds. 6th ed. American Or- (1986) summarized the characteristicsof Prairie Fal- nithologists’ Union, Washington, DC. con nest cliffs in the western US and found the cliffs BROWN,D. E. [ED.]. 1982. Biotic communities of the vary from 2-l 54 m tall (K = 29 m, n = 4 18), the mean AmericanSouthwest-United Statesand Mexico. nest height is 60%70% (X = 63%. n = 417) of cliff Desert Plants 4: l-342. height, and the exposureof nest cliffs (n = 188) tends CADE,T. J. 1982. The falcons of the world. Cornell to be southerly. Boyce (1987) measured 52 nest sites Univ. Press, Ithaca, New York. in the Mojave Desert, California, and found a mean ELY. C. A. 1962. The birds of southeasternCoahuila. cliff height of 29.3 m, a mean nest height of 18.3 m Mexico.‘ Condor 64:34-39. (62% of cliff height), and a mean southern exposure, ENDERSON,J. H. 1964. A study of the Prairie Falcon similar to the summaryby Runde and Anderson(1986). in the central Rocky Mountain region. Auk 81: Allen (1987a) found that Prairie Falcon nestsin North 332-352. Dakota are on small cliffs with a mean cliff height at HITCHCOCK,M. A. 1978. A nesting survey and eco- 34 nests of 11 m, a mean nest height at 33 nests of 7 logicalstudy of the PeregrineFalcon in the western m (64% of cliff height), and that cliffs facing southwest Chihuahuan Desert, 1976-1978. M.S.thesis, Sul seem to be preferred. Ross State Univ., Alpine, TX. The Prairie Falcon often is common (where it occurs) HUNT, W. G. 1976. Western Texas and northeastern in the arid and semi-arid desertsand steppesofwestem Mexico, p. 269-270. In R. W. Fyfe, S. A. Temple, SHORT COMMUNICATIONS 765

and T. J. Cade [eds.], The 1975 North American easternMexico, p. 377-388. In W. Swanson[ed.], PeregrineFalcon survey. Can. Field-Nat. 90:228- National Geographic Society Research Report, 213. 1977. Vol. 18. National Geographic Society, Hm, W. G., J. H. ENDERSON,D. V. LANNING, M. A. Washington DC. Hrrcucoc~, AND B. S. JOHNSON.1988. Nesting OGDEN, V. T., ANDM. G. HORNOCKER.1977. Nesting Peregrinesin Texas and northern Mexico, p. 115- density and successof Prairie Falcons in south- 121. In T. J. Cade, J. H. Enderson, C. G. Thelan- western Idaho. J. Wildl. Manage. 4 1:l-l 1. der, and C. M. White [eds.],Peregrine Falcon Pop- OLENDORFF, R. R., AND J. W. STODDART,JR. 1974. ulations: their management and recovery. Univ. The potential of management of raptor popula- Wisconsin Press, Madison. tions in western grasslands,p. 47-88. In F. N. INSTITUTODE GEOG~AF~A,UNIV. NAC. AuTCIN.Mnxrco. Hamerstrom. Jr.. B. E. Harrell. and R. R. Olen- 1970. Cartas de Climas: Chihuahua. Culiacan. dotIT [eds.], Management of raptors. Raptor Res. Hidalgo de1Parral, Monterrey, Nogales, Ojinaga; Rept. no. 2. and San Luis Potosi. Comision de Estudios de1 RUNDE,D. E.. AND S. H. ANDERSON.1986. Charac- Tenitorio National. 7 maps. teristics of cliffs and nest sites used by breeding LANNING,D. V., P. W. LAWSON,AND W. G. HUNT. Prairie Falcons. Raptor Res. 20:21-28. 1985. Ecology of the Peregrine Falcon in north-

The Condor93:765-768 0 The CooperOrnithological Society 1991

DEMOGRAPHY OF THE PIGEON GUILLEMOT ON SOUTHEAST FARALLON ISLAND, CALIFORNIA ’

DOUGLAS A. NELSON Department of Zoology, Universityof California, Davis, CA 95616

Key words: Demography; Pigeon Guillemot; Cep- from their wintering areas,and continuedobservations phus columba; seabirds;survivorship. until late July or August when chicks began to fledge. I also visited the island for one month in April 1981 Auks (Alcidae) form an important component of ma- and May 1982. rine avifaunas in the Northern Hemisphere, in terms In 1977, I studied about 10 pairs of guillemots that of numbers of both individuals and species.In order nestedatop a 40 m high ridge on Shubrick Point. After to effectively manage and protect alcid populations, 1977, I also made observations on the southeastside basic demographic data are vital (Nisbet 1979). De- of the island where approximately 20 pairs nested in mographic parametershave been estimated for five of or near a rubble pile at the head of a surge channel the six speciesin the North Atlantic (Hudson 1985). (East Landing). In contrast, survivorship of banded birds is known for Guillemots nested in natural and artificial crevices only one Pacific Ocean alcid species(Ancient Murrelet, at East Landing (Nelson 1987). Eight-nine guillemots Synthliboramphusantiques, Gaston 1990). In this note, were capturedwith leg noosesand banded with unique I report survivorshipand recruitmentof a color-marked combinations of two color bands and a numbered mo- sample of Pigeon Guillemots (Cepphuscolumba) over nel U.S. Fish and Wildlife Serviceband (Nelson 1987). a five-year period. To minimize nest desertion, I allowed birds to occupy a site for at least one week before capture. Additional METHODS birds were identified by unique tears or holes in their I observedPigeon Guillemots in 1977 and from 1979- webbed feet or by plumage marks in the white wing 1982 on SoutheastFarallon Island, California (37”42’N, patches.Birds were sexedby copulation position (Nel- 123QO’W) a 44 ha island about 43 km west of San son 1987). The Point Reyes Bird Observatory (PRBO) Francisco.Biological and physicalfeatures of the island also banded between 19 and 284 chicks annually since were describedbv Ainlev and Lewis ( 1974) and Ainlev 1970 with unique year-classcolor rings (Ainley et al. and Boekelheide-(1990): Among the ‘12 speciesof ma- 1990). Most of these birds were banded on Lighthouse rine birds breeding on SE Farallon is a population of Hill, about 200 m from my study sites.Several of these approximately 1,000 Pigeon Guillemot pairs (Ainley birds were in my study plot each year as territory own- et al. 1990). I beganobservations in March 1977, 1979 ers and non-territorial “loafers.” and 1980 before guillemots had returned to the island Survivorship of territory owners was estimated by resightingbanded birds and five birds with easily vis- iblei unique natural marks at Shubrick Point and East * Received 13 November 1990. Final acceptance5 Landing. This includesseveral pairs eachyear that held April 1991. territories but did not produceeggs (Nelson 1987). Sur-