DISTRIBUTION

Black Skimmers on the Mexican Plateau

"Black Skimmersshould now be consideredas occasionalvisitors to... Durango, Jalisco, and at leastformerly, Guanajuatoand the Valleyof Mexico."

Sartor O. Williams III

N NORTHAMERICA, the Black Skim- of the sightingit was apparent that the several meters. They then rested to- mer (Rynchopsnigra) is typically as- region had recently experiencedheavy gether on the far shore of the bay. They sociated with coastal situations. Inland rains, and throughout the morning the remained on shore for about 15 minutes, occurrences are generally considered wind was quite strong from the south. then took wing and began to skim the unusualand, while invariably newswor- On July 28, 1976, I found two Black bay again.At noon, as I was attempting thy, often appearas isolatedcases with- Skimmers at Laguna de Santiaguillo, to approach closer, the skimmers left out clear causal bases. Multiple sight- Durango (24ø50'N, 104ø55'W;elevation the bay and flew toward the open lake •ngs of birds from outside their normal 2000 m), a locality some 40 km north- During the period of observation, I ob- ranges or away from their expected west of Presa San Bartolo. I watched tained four pictureswith a 200 mm lens haNtats, however, can be important the two almost continuously from 10:45 and seven more with a 400 mm lens clues to the transpirationof significant a.m. until noon, usually through 8 x 40 Laguna de Santiaguillo is a large (13 km biologicalevents. In this paper I will (a) power binoculars, as I stood near the x 5 km), shallow, natural lake near the report three instances of Black Skim- spillway on the southeasternshore of villageof Guatimape, about 95 km north mers •n the interior highlandsof Mexico the lake. I first saw the skimmersas they of the city of Durango. The lake has no s•nce 1975; (b) review the validity of flew toward me from the open lake. natural outlet. A dam separatesthe per- past skimmer reports from the Mexican They immediately began to feed in a manent, northwestern portion of the Plateau; and (c) discussthese events as shallow bay some distance from me, lake from a vast, seasonally flooded regards weather phenomena, recent crisscrossingthe placid surfacein typi- playa to the southeast.The "bay" where skimmer dispersalinto the southwest- cal skimmer fashion. The two, both in the skimmers fed was actually a flooded ern United States, and annual ecolog- adult springplumage, stayed together at pasture. Livestock were grazing the ical eventsin the Mexican highlands. all times, although when skimming one higherground, while six fishermenwere On August 13, 1975, M. R. Baker and would occasionally trail the other by hauling seines through the shallows I were surprisedto find two Black Skim- mers at Presa San Bartolo, Durango (24ø32'N, 104ø40'W;elevation 1940 m). We s•ghted the two skimmers re- peatedly,often at very closerange, dur- ing a two-hour (10:00-12:00 a.m.) boat- •ng c•rcuit of the reservoir. Both birds were •n adult "spring" plumage (black above, with no white collar on the hind- neck)and appearedto be in goodphysi- cal condition. The skimmers were con- hnually in the air, sometimes flying to w•th•n a meter or two of the water's choppy surface,but we never saw them attempt to feed. The two were always together over the reservoir; they called occasionallybut generally were silent. W•th a 200 mm lens I obtained 10 color shdes of the skimmers at various times dunng the morning. Presa San Bartolo, a shallow reservoir of about 1700 ha, is located in central Durango near the town of Canatlfin, approximately 55 km MEXICO "• north of the city of Durango. On the day Figure 1. Map of Mexico showinglocation o,f places mentionedin the text. Map by S.R.D

Volume 36, Number 3 255 The region had received heavy rains, provided more specificinformation, in- history museum at the university in typical of the season,during the preced- cludmgpointing out that the pair that he Guanajuatois today namedin honor of ing several days. By 3:30 p.m., on the encounteredconstituted the only record Dr. Dug•s). Both were in professional day of the sighting,torrential rains were during his several years study of the contactwith noted nineteenthcentury falling, causingflash-flooding in nearby avifauna of the valley. A third nine- ornithologists in other countries It villages. teenth-century highland record is pro- would seem remarkable that these men vided by a specimenreportedly taken could have mistakenso singulara bird N THEMORNING OF MAY 24, 1978, near Mexico City by the collector G. H. asa skimmer.In addition,the Bafio (the during an aerial survey of water- White (Sclater 1864: 179). This speci- valley and !ake region immediately birds on the Mexican Plateau, C. E. men is probably the basis for Sanchez southof the city of Guanajuato)and the Knoder, P. D. Plaza, and I observed a (1878: 108) having included the Valley Valley of Mexico were, and to an extent flock of eight Black Skimmers at La- of Mexico within the area of geographic still are, likely places for such water- guna de Atotonilco, Jalisco (20ø25'N, distribution of the skimmer in Mexico. birds as skimmers,stray or otherwise, 103ø40'W; elevation 1500 m). These These three early highland records, to occur. birds, obviously disturbed by our air- representing two localities, were ac- craft, were seenflying toward the open cepted without questionby Salvin and DISCUSSION lake from the vicinity of the eastern Godman (1903: 416). They may have shore. Although we observed the birds overlookedthe fact that, several years NTHE UNITED STATES, inland occur- only briefly, we had no dotibt concern- earlier, Herrera (1887b: 319) had rences of skimmers usually produce lng their identity as skimmers. Although pointed out the unreliability of the speculationas to why thesebirds should it went unrecorded at the time, I believe locality data of many of White's speci- appear away from the sea. More often all the birds were spring-plumaged mens. The latter were often purchased than not, weather disturbances have adults. Laguna de Atotonilco is a large in native markets in Mexico City and been implicated in these records and, (12 km x 4 kin), shallow lake lying in a some of these could well have come indeed, most inland records in the closed basin in central Jalisco. It is from lowland areas. Ridgway (1919: United States have occurred during the situated near the town of Acatlfm de 453) followed Salvin and Godman by summer-fall period of warm weather Jufirez and is about 40 km southwest of including the three interior records; disturbances.Although some question Guadalajara. The weather on the day of however, he placed question marks has arisen concerning weather as a the sightingwas clear but quite hazy, as after the records that originated with cause of such vagrancy (e.g., Kaufman is typicalfor the regionprior to the onset Dug•s and Herrera. Why Ridgway did 1977: 151-152), Anderson et al. (1977 of the rainy season. this is not clear--it may have been due 234) have concludedthat dispersalof to lack of supportivespecimens and/or certain marine birds into the southwest- his uncertaintyas to which subspecies ern United States is weather-induced I might have been involved. He ascribed analyzed availableweather data for the White's specimento the nominaterace, three-weekperiod preceding each of my underwhich he also placedthe records three sightingsbut foundno particularly of Dug•s and Herrera. unusual weather phenomenaon either After Ridgway, however, these old Mexican coast that might have driven recordsapparently fell into disfavor, as seabirds inland. It is conceivable that, all subsequent works on the birds of as nocturnal feeders, Black Skimmers Mexico have either dismissed them as could be subjectto displacementby the unfoundedor ignoredthem altogether. severe, nighttimestorms that frequently Figure 2. Black Skimmer over Presa San Hellmayr and Conover (1948: 339-345), occurin coastalareas of Mexico dunng Bartoreo, Durango. Photo/S.O. perhaps aware of the uncertainty sur- the summer rainy season,and be carried Williams 111. rounding White's specimens and ob- over the sierra and into the interior Although these recent occurrencesof serving that Ridgway had seemingly However, while I cannot discount Black Skimmers on the high interior questioned the records of Dug•s and weather entirely, I doubt that all of tableland of Mexico are somewhat sur- Herrera, listed no inland localities for these three recent occurrences repre- prising,they are not without precedent. skimmers in Mexico. The most recent sent storm-driven strays. Over a century ago, Dug•s (1869: 142) compendiumof the distributionalstatus It is notable that recent influxes of recorded the speciesfrom the state of of Mexican birds statesflatly: "very old skimmers have occurred into California Guanajuato. Later, Herrera (1887a: reportsfrom the interior deserveno cre- and Arizona--almost certainlyfrom the 188)recorded it from the Valley of Mex- dence and remain unconfirmed" (Fried- west coast of Mexico (McCaskie et al ICO (the closed basin in the immediate mann et al. 1950: 112). 1974: 338, Grant and Hogg 1976 79, vicinity of Mexico City, which includes In retrospectI believe the records of Witzeman et al. 1977: 1172). Skimmers portionsof the Distrito Federal and the Dug•s for Guanajuato and Herrera for occur regularly in the latter region, from state of Mexico and which lies at an the Valley of Mexico are probablyvalid, the Gulf of California southward Al- elevation of about 2200 m). Dug6s re- whereasthat of White may be question- thoughseparated by imposingmountain corded the species without comment, able and perhapsshould be discounted. ranges, my highland localities •n Du- applyingthe acceptedbinomial plus the Both Dug•s and Herrera appearto have rango are only 250 km from coastal vernacular name "pico de tijera" in a been competent and respected natu- Sinaloa, and the Jalisco site is but 150 distributional list of vertebrates that he ralists, with some training in ornithol- km from the coast of Colima. In the had encountered in the region. Herrera ogy, including taxonomy (the natural coastal lagoons near Manzamllo,

256 AmericanBirds, May 1982 Knoder, Plaza, and I recorded several gree It •s of•nterest that in E1 Salvador, persal of Cahforma Brown Pehcans hundred Black Skimmers •n a large nest- Dickey and van Rossem (1938. 184) re- Btrd-Bandmg 48 228-238 corded Black Skimmers inland at Lake BEHRSTOCK, R. A. 1977. Notes on •ng colony of Laughing Gulls (Larus some northern birds wintering on the atrtcdla) on May 24, 1978. Taken to- Olomega on several dates during Au- Pacific coast of Guatemala. Am. Birds gether, the California, Arizona, and my gust; however, they could not deter- 31: 382. Mexican records may signal a recent mine if the birds came from the ocean DICKEY, D. R., and A. J. VAN ROS- each night or were migrantsthat simply SEM. 1938. The birds of El Salvador expansionin the rangeof the skimmer, Field Mus. Nat. Hist., Zool. Set., Vol owing to such factors as increases in stoppedto feed. 23: 1-609. numbers, displacementdue to environ- Regardlessof how or why they arrive DUG•S, A. 1869. Catfilogode animales mental factors, or other, unknown there, Black Skimmers should now be vertebrados observados en la Repfibhca causes The recent (winter 1975-76) ap- considered as occasional visitors to the Mexicana. La Naturaleza, Ser. 1, Vol 1: 137-145. Mexican Plateau, occurringin Durango, pearance of hundreds of Black Skim- FRIEDMANN, H., L. GR1SCOM, and R mers along the Pacific coast of Jalisco, and, at least formerly, Guana- T. MOORE. 1950. Distributional check- Guatemala (Behrstock 1977: 382), after juato and the Valley of Mexico. How- list of the birds of Mexico, Part 1 hawng gone unreported from that coun- ever, potentialnesting in the highlands Pacific Coast Avifauna 29: 1-202. try s•nce 1863 (Salvin 1865: 193, Land by skimmers seems most unlikely, at GRANT, G. S., and N. HOGG. 1976. Be- havior of late-nestingBlack Skimmers 1970 ll4), may indicate that there are least during the summer, in view of the at Salton Sea, California. WesternBirds more skimmers along the Pacific coast continually rising water levels during 7: 73-80. now than were there previously. How- the June-October rainy season, which HELLMAYR, C. E., and B. CONOVER ever, recent expansion would not ex- would likely prove detrimentalto sand- 1948. Catalogue of birds of the Americas and the adjacent islands plain the older Mexican Pleateau rec- bar-nestingspecies such as skimmers. Field Mus. Nat. Hist., Zool. Set., Vol ords Finally, it should be noted that while 13, Part 1, No. 3: 1-383. these Mexican occurrences undoubt- HERRERA, A. L. 1887a. La migraci6n en T MAYBE THAT THESE highland rec- edly representaltitude recordsfor the el Valle de M•xico. La Naturaleza, ords are not weather- or expansion- speciesin North America, they do not Ser. 2, Vol. 1: 165-189. --. 1887b. Notas acerca de los verteb- related at all, but instead they may approachthose for South America re- rados del Valle de M•xico. La Natu- reflect a small, perhaps regular move- ported by Murphy (1936: 1173) and raleza, Set. 2, Vol. l: 29%342. ment by nonbreedersup to plateau wet- others from Lake Titicaca in Peru (ele- KAUFMAN, K. 1977. The changing sea- lands During my fieldwork in Mexico, I vation 3800 m), which must remain the sons. Am. Birds 31: 142-152. LAND, H. C. 1970. Birds of Guatemala observedthat several other speciesthat altitudinal "high" for the species and Livingston Publ. Co., Wynnewood, typically nest in coastal or lowland probably for the genusas well. Pennsylvania. 381 pp. areas, notably Roseate Spoonbills MCCASK1E, G., S. LISTON, and W. A (Adata ajaja) and Wood Storks (Myc- ACKNOWLEDGMENTS RAPLEY. 1974. First nesting of Black terra americana), occur in flocks of up Skimmers in California. Condor 76 337-338. to 400 and 50 individuals, respective- Y FIELDWORKIN MEXICO was MURPHY, R. C. 1936. Oceanic birds of ly, in the highlands during the summer fundedprimarily by a doctoralfel- South America, Vol. 2. Am. Mus. Nat season Similarly, I have found during lowshipfrom the Welder Wildlife F6un- Hist., New York. Pp. 641-1245. this seasonthat Caspian Terns.(Sterna dation, with additional support being RIDGWAY, R. 1919. The birds of North and Middle America. Bull. U.S. Natl [=Hydroprogne] caspia), heretofore providedby the National AudubonSo- Mus. 50, Part 8: 449-457. unreportedfrom anywhereon the Mexi- ciety and the U.S. Fish and Wildlife SALVIN, O. 1865. The sea-birdsand wad- can Plateau, occur in flocks of up to 30- Service. I thank John P. Hubbard, Allan ers of the Pacific coast of Guatemala 40 "spring-plumaged" adults at wet- R. Phillips, and Ronald A. Ryder for Ibis 1865: 187-199. and F. D. GODMAN. 1897-1904 lands in the highlands of Jalisco. reading and providing helpful com- B'iologiaCentrail-Americana. Aves, Furthermore, ! have observed Laugh- ments on an earlier draft of this paper. Vol. 3. London. 510 pp. •ng Gulls in the highlands of central Discussions with Thomas B. McKee, SANCHEZ, J. 1878. Datos para el Durangoin July, and Amadon and Phil- Department of AtmosphericSciences, catfilogo de las aves que vivan en hps (1947: 577) collected one there in Colorado State University, and corre- M•Sxico. Anales del Mused Nacional de August; there are additional Laughing spondencewith PaulR. Julian,National Mdxico, Ser. 1, Vol. 1: 92-110. SCLATER, P. L. 1864. List of a collection Gull records for highland lakes in Center for Atmospheric Research, of birds procured by Mr. George H Jahsco, Michoacfin, Guanajuato, and Boulder, Colorado, were most helpful White in the vicinity of the City of the Valley of Mexico (Friedmann et al. to my understandingof the possiblein- Mexico. Proc. Zool. Soc. London 1864 1950 105). fluence of weather on these records. I 172-179. WlTZEMAN, J., J.P. HUBBARD, and The attraction of these highlands to am grateful to Karl F. Lueder for his K. KAUFMAN. 1977. The nesting sea- suchspecies during this seasoncould hospitality during my residence in son: southwest region. Am. Birds 31 possiblybe relatedto the abundanceof Chapala, Jalisco. 1171-1176. small, freshwater fishes in the shallow lakes and seasonal reservoirs of the LITERATURE CITED plateau.At least,it appearsthat several -Department of Fishery and typically coastal speciesof birds regu- Wildlife Biology, Colorado State AMADON, D., and A. R. PHILLIPS. University, Fort Collins, CO larly invadethe plateauand exploitthis 1947. Notes on Mexican birds. Auk 64: 80523. Present address resource, although this movement 576-581. couldperhaps be due to their beingdis- ANDERSON, D. W., L. R. DEWELSE, 428 PennsylvaniaAve , placedfrom the lowlandsto somede- and D. T. TILLER. 1977. Passive dis- Shieveport,LA 71105

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