Table Of Content

Short Communications Wilson Bulletin 1 16(4):352-354, 2004 Group Roosting Behavior of Yellow Tyrannulets (Capsiempis flaveola) Stefan Woltmann* — ABSTRACT. For4consecutiveevenings in south- son (Skutch 1989, Mayer 2004). Some tropi- ern Nicaragua, a group of three Yellow Tyrannulets cal tyrannids that build covered or globular {Capsiempisflaveola) roosted in the same plant, and nests also roost (either individually or with always arrived approximately 45 min before last light. Pre-roosting behavior appeared stereotyped and in- young) in these structures year-round (Fluvi- cluded mutual preening and a peculiar mannerofhop- colinae: Sulphur-rumped Flycatcher, Myiohius ping over one another. These three birds presumably sulphureipygius', Skutch 1989), and Eye- left the roost around first light each morning. Received ringed Flatbills (Platyrinchinae: Rhynchocy- 4 May 2004, accepted 6 October2004. clus brevirostris) sometimes build a different type of nest for roosting than for breeding (Skutch 1960). I describe here observations of Despite the large amount of time birds the roosting behavior of a group of three Yel- spend at roost sites and their presumed vul- low Tyrannulets (Elaeniinae: Capsiempisflav- nerability while asleep, little is known about eola), whose roosting behavior has not been roosting behavior of most species, especially described previously. those in the Neotropics. Skutch (1989) pro- The Yellow Tyrannulet (7.9 g) is a sexually vides a general overview of avian roost sites monomorphic, open-cup-nesting, lowland ty- and behavior, especially of Neotropical pas- rannid, resident from eastern Nicaragua south serines. Among the Tyrannidae, Skutch (1989) across northern South America, and disjunct- reported “sleeping in contact” in both Platyr- ly(?) from Bolivia east into southeastern Bra- inchinae (Common Tody-Flycatcher, Todiros- zil (Ridgely and Gwynne 1989, Ridgely and trum cinereum) and Tyranninae (Social Fly- Tudor 1994, Hilty 2003). In Central America, catcher, Myiozetetes similis; Tropical King- it lives in pairs or small (possibly family) bird, Tyrannus melancholicus), whereas groups in lowland thickets, overgrown pas- “sleeping in pairs” (i.e., roosting in close tures, and forest edges (Skutch 1960, Ridgely proximity, but not in contact) was noted in and Gwynne 1989; SW pers. obs.), but is of- Tyranninae (Gray-capped Flycatcher, Myioze- ten associated with bamboo in South America SW tetes granadensis; Boat-billed Flycatcher, Me- (Ridgely and Tudor 1994; pers. obs.). The garhynchus pitangua) and Elaeniinae (Yel- observations reported here were made in the low-bellied Elaenia, Elaenia flavogaster). In evening, 6-9 April 2004, at the confluence of these examples, the roosting groups consist of the Rio Bartola and Rio San Juan, Refugio a few individuals known or suspected to be Bartola, Depto. Rio San Juan, Nicaragua (10° paired or related. Cooperatively breeding 58' N, 84° 20' W; 30 m asl). Daytime tem- birds may be particularly prone to roosting in peratures were approximately 30° C, dropping contact (Skutch 1989), but few tyrannids are to 22—25° C at night; there was no precipita- reported or suspected to breed cooperatively tion during this period. Observations were (2-3 species out of >375), and these species made at the edge ofa clearing, where an over- may not always do so (Thomas 1979, Ricklefs grown pasture and secondary forest growth 1980, Brown 1987; J. A. Mobley pers. met. The 1.5-ha pasture was adjacent to the comm.). Migratory kingbirds (Tyranninae: Rio San Juan, and consisted mostly ofgrasses m Tyrannus spp.) have been observed roosting (1.5-2 high) interspersed with clumps (1.5- in large groups during the non-breeding sea- 3 m high) of an unidentified slender, woody legume with finely pinnate leaves and yellow ' Dept, of Ecology and Evolutionary Biology, 310 flowers. Dinwiddle Hall, Tulane Univ., New Orleans, LA On 6 April, at 17:40 CST (~15 min before 70118, USA; e-mail: [email protected] sunset; 35 min before complete darkness). 352 SHORT COMMUNICATIONS 353 three Yellow Tyrannulets appeared, giving niine and tyrannine tyrannids, and most often many single “wit” or “weet” notes. These involves young siblings, or young and their I vocalizations, while having a quality charac- parents; adult mated pairs apparently roost teristic of the species, were unlike the typical less often in direct contact with each other two-syllabled calls given while foraging and (Skutch 1989). at other times of the day. In contrast to the During the next 3 evenings, the birds ar- shy behavior of this species described by rived slightly earlier (17:20-17:30), did not Skutch (1960), the birds were unwary, and vocalize as much as on the first evening, and gave no indication of being disturbed by my were always settled by 17:35. It was not pos- presence 15 m away. While making many sible to determine whether the birds always short flights and hops through the vegetation, approached the roost site from the same di- the group quickly converged on the roost rection or traveled together, but each evening plant, a thin woody legume (2.2 m high) en- they appeared synchronously from the vege- twined by a vine with cordate leaves. The tation surrounding the roost plant. A few spo- m birds all perched on the same branch 1.5 radic observations of Yellow Tyrannulets in above ground, which placed them at the lower the pasture during the day were all of single edge ofthe plant’s foliage. The birds’ position individuals, but it was difficult to determine i left them completely exposed on three sides, whether or not other individuals were nearby but leaves from the plant and asso—ciated vine in thick vegetation. The birds always roosted provided total cover from above roost-site in the same plant and alternated daily between characteristics that Skutch (1989) reported for roosting on one of two branches that were several other tyrannids. only a few centimeters apart. On one evening, ^ Upon alighting on the roost branch, the after the birds had already settled, the birds ' birds appeared to “jockey” for position, fre- were flushed from the roost by a pair ofGray- quently hopping over one another. This could ish Saltators {Saltator coerulescens). The tyr- have been an effort to gain the centerposition, annulets returned, briefly jockeyed for posi- i but it was not uncommon for two birds to en- tion, engaged in some mutual preening, and gage in this hopping while the third looked on settled again within 4 min. Roost site fidelity from a branch a few centimeters away. This in birds is not uncommon (Skutch 1989, Wil- hopping behavior appeared highly stereo- lis and Oniki 2003), but because 1 was only typed: a bird hopped over a single adjacent able to check the roost site for these 4 con- bird, and the hopping bird alit as close as pos- secutive days, I do not know how frequently sible to the bird it hopped over. Sometimes the the site was used otherwise. hopping bird simply walked quickly over the I was unable to determine precisely when back of its neighbor, but more typically the the birds left the roost in the morning. On 2 hopping was of the same character as that of mornings, 1 checked the roost at 05:30 (—25 ' the hopping exhibited by some male manakins min after first light) and the birds were already (Pipridae) at leks. During this time, the birds gone. 1 made one check of the roost at 04:30 I frequently vocalized and faced opposite direc- (total darkness) with a flashlight, and the birds tions, but after 7 min they became silent and were still asleep at the roost. Thus, these birds all faced the same direction. Once settled, the probably left the roost somewhere around first three birds were in direct contact with each light. other and the contour feathers were fluffed out Despite observing the tyrannulets at close somewhat. The birds remained in this posi- range with binoculars, 1 was unable to detect tion, eyes open and looking about, until total any differences in plumage (U' behavior that darkness. The most common position for the might suggest something about the relation- group entailed all birds facing the same direc- ship of the birds. Yellow Tyrannulets breed at tion, the middle bird looking straight ahead, almost any time of year (in Costa Rica) and and both outer birds looking away from the lay two eggs per clutch (Skutch 1960): thus, ( i center one; this was the position the birds it is not likely that this was a group of three were in at the end of my observations on all young siblings roosting together, as Skutch 4 evenings. Roosting in direct contact with (1989) describes for a group of Rusty-mar- I other individuals has been noted in both clac- gined I lycatchers. Only the female is thought 354 IHE WILSON BULLETIN • Vol 116, No. 4, December 2004 to incubate eggs in Yellow Tyrannulets, but Hilty, S. L. 2003. Birds ofVenezuela, 2nded. Prince- the male helps feed the nestlings (Skutch ton University Press, Princeton, New Jersey. 1960). Extra-pair helpers at the nest are not Mayer, S. 2004. BirdsofBolivia2.1 (CD-ROM). Bird Songs International, Westernieland, The Nether- known for Yellow Tyrannulets, and generally lands. are rare among tyrannids (Brown 1987). Thus, Ricklefs, R. E. 1980. ‘Watch-dog’ behaviourobserved I may have been observing two adults with at the nest ofa cooperative breeding bird, the Ru- one young, one adult with two young, or three fous-margined FlycatcherMyiozetetescayanensis. agdeuslttss.thEaitthtehre oyfouthneg fsirtsatytwwiothsctehneairriopsarseungt-s RidgetIobliyst,he1R2.b2i:Sr1.d1sa6o-n1fd1Pj8a..naa.maG,wywnitnhe,CoJsrt.a1R9i8c9a.,ANigcuairdae- until their plumage appears (at least under gua, and Honduras. Princeton University Press, held conditions) identical to that of the adult. Princeton, New Jersey. Ridgely, R. S. and G. Tudor. 1994. The birds of ACKNOWLEDGMENTS South America, vol. 2: the suboscine passerines. University ofTexas Press, Austin. I am grateful for the hospitality of the staff at Re- Skutch, A. F. 1960. Life historiesofCentral American fugio Bartola, and thank the Louisiana Board of Re- birds II. Pacific Coast Avifauna, no. 34. gents for financial support. I thank T. W. Sherry, J. A. Skutch, A. F. 1989. Birds asleep. University ofTexas Mobley, and two anonymous referees for providing Press, Austin. constructive comments on this note. Thomas, B. T. 1979. Behavior and breeding of the White-bearded Flycatcher {Conopias inornata). LITERATURE CITED Auk 96:767-775. Willis, E. O. and Y. Oniki. 2003. Roosting and nest- Brown, J. L. 1987. Helping and communal breeding ing of the Burnished-buffTanager (Tangara cay- in birds. Princeton University Press, Princeton, ana) in southeastern Brazil. Ornitologia Neotrop- New Jersey. ical 14:279-283. Wilson Bulletin 116(4):354-356, 2004 Foraging by a Red-tailed Hawk along a Wetland Edge: How Large a Duck can be Captured? Joseph R. Jehl, ABSTRACT—A Red-tailed Hawk (Buteo jamai- ing” were formalized (e.g., Krebs and Davies censis', estimated mass 1,000-1,200 g) failed to kill a 1978). Originally, their interest was practical Red-breasted Merganser (Mergus serrator, estimated and involved questions such as what size prey cmma)s,sb1u,t15e0vigd)entthlayt idtiscpaapttcuhreedd ainssthaarvlilnogw Rweadte-rne(c<k2e5d a hawk could bring to the table. Much later, Grebe (Podiceps grisegena\ mass 645-660 g). These with the rise of wildlife management pro- observationsarepertinenttoestimatingtheuppermass grams, raptor enthusiasts turned to broader limit for successful foraging in water. Received9April ecological questions, including the impact and 2004, accepted 2 September 2004. selective effects of predators on prey popula- tions (e.g., Rudebeck 1950, 1951; Craighead Falconers were familiar with prey selection and Craighead 1956; Luttich et al. 1970). In centuries before ideas about “optimal forag- a classic study involving four species (Accip- iter nisus, Falco columbarius, F. peregriniis, ‘ Div. of Birds, U.S. National Museum of Natural Haliaeetus albicilla), Rudebeck (1950, 1951) History, Smithsonian Inst., Washington, DC 20560, reported that an average of 19% (range: 14- USA. 33%) of birds captured for prey “exhibited ^Hawk Mountain Sanctuary, Acopian Center, 410 Summer Valley Rd., Orwigsburg, PA 17961, USA. injury, abnormality, or abnormal behavior.” Current address: 2752 Poplar Ln., Annapolis, MD From this he concluded that raptors probably 21401, USA; e-mail: [email protected] selected weak or unfit birds in numbers dis-