514 SHORT COMMUNICATIONS methods to the assessmentof genetic mating sys- the evolution of vocal soundsused at close range. tems in vertebrates,p. 133-161. In J. D. Ferraris Proc. Int. Ornithol. Congr. 18:737-741. and S. R. Palumbi [eds.], Molecular zoology: ad- MORTON,E. S., AND K. C. DERRICKSON.1996. Song vances, strategiesand protocols.Wiley-Liss, New ranging by the Dusky Antbird, Cercomacra tyr- York. ann.ni ranging without song learning. Behav. FLEISCHER,R. C., C. L. TARR,AND T. K. PRATT.1994. Ecol. Sociobiol. 39: 195-201. Genetic structureand mating system in the Palila, ROBERTSON,B. C., AND J. K~KKAWA.1994. How do an endangered Hawaiian honeycreeper, as as- they do it?-Monogamy in Zosterops lateralis sessedby DNA fingerprinting. Mol. Ecol. 3:383- chlorocephala. J. Ornithol. 135:459. 392. SEUTIN,G., B. N. WHITE,AND I? 'I BOAG. 1991. Pres- JEFFREYS,A. J., V WILSON,AND S. L. 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MORTON. social systemsin northern Venezuelan habitats,p. 1990. The ecology and evolution of extra-pair 233-259. In J. Eisenberg [ed.], Vertebrateecology copulation in bird<: Current Omithol. 7:330-369. in the northern Neotropics. Smithson. Inst. Press, WINGFIELD.J. C., AND D. S. FARNER.1976. Avian en- Washington,DC. docrinology-field investigations and methods. MORTON,E. S. 1980. The ecological backgroundfor Condor 78:570-573. The Condor 99~514-519 Q The CooperOmlthological Society 1997 ON THE BEHAVIOR OF THE BLACK SWIFT ’ MANUEL MAR~N Museum of Natural Science and Department of Zoology and Physiology, Louisiana State University, Baton Rouge, LA 70803 and Western Foundation of Vertebrate Zoology, Camarillo, CA 93012, e-mail: [email protected] Abstract. The behavior of Black Swifts was stud- then most roostedon the cave walls. During incubation ied in southern California from 1990 to 1992. Four and early brooding, an adult always remained at the types of aerial interactions were distinguished: (a) nest, and food transfer between adults was observed group chase, (b) pair chase, (c) pair contact, and (d) during this period. touch and grasp. The latter two interactions can be Key words: behavior, aerial and hostile displays, intraspecificor interspecific.Aerial copulationwas not begging, roosting, Cypseloides niger. observed. Nestlings, from age 18 days onward, and adultsgave hostile or deterrencedisplays by wing-rais- ing. Begging by nestlings was silent but aggressive Swifts as a group are remarkably uniform in shape, toward the adult. Silent begging may be an antipre- which makes them difficult to identify, and their aerial dator strategyfor a speciesthat producesa single chick lifestyle makes them difficult to observe. As a result, per season. Nestlings have a far more conspicuous little is known about their behavior, even for common white facial marking than adults; this may function as species. This is especially true in the New World a target signal to guide food delivery in the dimly lit swifts. nesting conditions and as an aid for the adult to find The subfamily Cypseloidinae contains 12-l 3 spe- the nest when arriving late at night. Adults roostedon cies, most of which are tropical or semitropicalin dis- the nest for the first half of the nestling period and tribution. All are similar in body shape,and most have uniform dark plumage and facial markings, which in some are distinctive. All speciesin the subfamily nest I Received 8 March 1996. Accepted 29 November in sites behind waterfalls, in caves, or deep gorges,on 1996. sea cliffs, and in sea caves. Moisture, inaccessibility SHORT COMMUNICATIONS 515 to terrestrial predators, and darknessor at least deep flew horizontally, and the secondbird approachedfrom shade during most of the day seem to be the rule for below. Next they turned over and clashed or almost nest sites within the group. touched with the feet. Sometimes one bird emitted The Black Swift, Cypseloides niger, is a widely dis- clicking notes. After a few seconds, the higher bird tributed species, found locally from northwestern changedits direction of flight, and the lower bird con- North America through Middle America and the West tinued in horizontal flight. Occasionally,two birds be- Indies (AOU 1983). Despite its wide range, most of came involved in a fourth type of aerial interaction, what is known about the species is limited to infor- “touch and grasp,” in which the birds grasped each mation on distribution and breeding biology (Knot-r other by the feet and tumbled downward for a few 1961, Foerster and Collins 1990). In this paper aerial meters, sometimes several meters, occasionally sepa- interactions,hostile displays, begging behavior, roost- rating just above the vegetation. Subsequently,they ing, and possiblepair bond behavior are described. rejoined the group (if any) above. Both the third and the fourth type are likely aggressiveinteractions. STUDY SITE AND METHODS On four dates in 1992, Black Swifts were observed The biology of the Black Swift was studied in the San in aerial interactionsof the third and fourth types with JacintoMountains in the vicinitv of Idvwild. Riverside Violet-green Swallows (Tuchycinetu thnlassina). Co., southernCalifornia. Most observationswere con- These aerial interactions were observed when the ducted at a single site where an aggregation of 6-7 swifts flew over the top of the pines in a section of the pairs nested every year. From 1990 to 1992, the area canyon where a group of swallows usually foraged. was visited 40 times. Visits were made at l-15 day When a swift approachedthe swallow flock, a swallow intervals, with observation periods ranging from l-3 would chase the swift, and they would graspeach oth- days. The area immediately surroundingthe site was ers’ feet. Sometimes this action was just a brief dash covered by coniferousforest. The nesting site, at 1,500 or a short descent,with birds being graspedby the feet m elevation, was a cave formed by large boulderswith as in the third and fourth interaction types described a substantial flow of water through a side wall and above. On 8 July 1992, I photographedone of these several minor drips in the cave ceiling. Water flowed interspecific interactions (Fig. 1). This type of inter- through the stream year-round, but substantialdiffer- specific aggressionalso occurred intraspecifically(see ences occurred among years and the flow declined below). from beginning to end of summer. More detailed in- Aerial interactionsof the third and fourth types de- formation on the vegetationand site of the area can be scribed above, in which two birds graspedeach other found in Barbour and Major (1977) and Foerster and by the feet while descendingearthward, have been re- Collins (1990). garded as aerial copulations (e.g., Foerster 1987). Whether in swifts these aerial interactionsare actually RESULTS AND DISCUSSION copulations has been controversial (Marin and Stiles AERIAL INTERACTIONS 1992). In other swifts, similar interactionshave been observed or photographed,but not considered copu- For much of the breeding season(May-September) I lations (Francis 1987). Copulation at the nest has been observed the birds in several types of aerial interac- reported for many swifts in other genera, e.g., Apus tions, primarily in the vicinity of the breeding site. I (Moreau 1942, Lack and Lack 1952), Chaeturu (Fi- was able to distinguishfour types of aerial interactions, scher 1958), Collocalia (Medway 1962), Cypsiurus not all related to courtship.The first type, which I des- (Fry et al. 1988), and Streptoprocne (Rowley and Orr ignated as “group chase,” was a horizontal flight dur- 1962). ing which one of the birds led a high-speedchase. The Becausethese aerial interactionscan be interspecif- leading bird (presumably a female) usually was fol- ic, I question whether such behavior involves copula- lowed by 3-6 birds; one or more of the chasing birds tion. It is more likely that aerial interactionsof types emitted soft high-pitched sounds.Although flight was three and four are a form of aggressionrather than occasionally erratic, all birds remained close together sexual behavior. This reasoningmay apply to many if at high speeds, and the group seemed well synchro- not all swifts. nized. Group chasesmay involve the formation of new pairs or pair bond reinforcement. They mainly oc- HOSTILE DISPLAY curred early in the season. The second kind of aerial interaction was “pair The wing-raising display appearsto be used to intim- chase.” Usually, but not always, this began when a idate an opponent or predator. When incubating or pair was moving in a continuous horizontal flight. brooding, adult Black Swifts did not leave the nest, Sometimes this type of chase split off from a group and when I approachedthem closely, they reacted by chase, with two birds separatingfrom the group, and raising the wings. A similar intimidation display seems subsequentlythe birds would make a high-speed dive to be performed by adults in many swift species,e.g., and follow each other closely in erratic flight maneu- Chaeturu SDD.