The Condor 90:607412 0 The Cooper OrnithologicalSociety 1988

THE GRAY-BREASTED CRAKE (LA 27X4LLUS EXILIS) IN COSTA RICA: VOCALIZATIONS, DISTRIBUTION, AND INTERACTIONS WITH WHITE-THROATED CRAKES (~5.ALBIGULARIS) l

F. G. STILES Escuelade Biologta.’ Universidadde CostaRica, Ciudad Universitaria “Rodrigo Facie, ” CostaRica, Central America

D. J. LEVEY Department of Zoology, 223 Bartram Hall, Universityof Florida, Gainesville,FL 32611

Abstract. We provide the first documentation ofLaterallus exilis in Costa Rica. Because of its secretive nature, little is known about this species.We describe the coloration of its soft partsand contrastits vocalizationswith those of L. albigularis,a common and sympatric congener. In Costa Rica, L. exilis apparently breeds during the rainy season.Contrary to previous beliefs, L. exilis appearslocally common and widespreadin Costa Rica. Although it appearsmost common in wet pastures,its habitat preferencesshift seasonally,in response to fluctuating water levels. BecauseL. albigularis occupiesthe same types of habitat, we looked for evidence of interspecific interactions. We found that each speciesresponded to playbacksof each other’s vocalizations and that seasonalhabitat shifts appearedreciprocal. Thus, we suggestthat the coexistence of these rails is a dynamic process, mediated by interspecificterritoriality and/or aggression. Key words: Laterallus exilis; Laterallus albigularis; vocalization;habitat; Costa Rica; interspecificinteractions; rails.

INTRODUCTION south! Brief notes on the ’s habitat have been The crakes of the Laterallus, collectively provided by Miller (1960), Wetmore (1965) Sto- the least-studied group in the family Rallidae rer (198 l), and Hilty and Brown (1986); the latter (Ripley 1977) are extremely secretive denizens authors provide descriptions of some of the calls of thick grassyor marshy vegetation, which they of L. exilis. Surprisingly, the nest and eggsof L. scarcelyever leave. The natural history of many exilis were described long ago from Trinidad speciesis very poorly known, even though the (Belcher and Smooker 1935) but no additional themselves may be widespread and even reports of nesting have been published. locally common. The Gray-breasted Crake, L. In Central America, L. exilis was long known exilis,is just such a species,being known from only from two specimens taken a century ago lessthan 50 specimensover its entire range from near the Nicaragua-Honduras boundary (Howell Belize to Paraguay (AOU 1983). Indeed, many 1957). Since then, five additional specimensbut of the specimenswere obtained without the birds few biological data have been obtained from Be- ever being seen in the field by the collector. Two lize, Honduras, Nicaragua, and Panama (Howell were caught by hand by men clearing tracts of 1957, Wetmore 1965, Russell 1966, Monroe marshy ground (Wetmore 1965); one was brought 1968). The speciesis still widely regardedas rare in by a house cat (Howell 1957); yet another was and local (e.g., Blake 1977). In this paper we caught in a mammal trap set in a rodent runway present the first reports of L. exilis from Costa (Storer 198 1). That the bird is often overlooked Rica, where it is far more common and wide- over wide areas is attested to by Storer’s (198 1) spread than previously suspected.We also de- specimen from Paraguay, which extended the scribe its vocalizations, soft-part colors, habitat, species’ known distribution 1,500 km to the and interactions with its abundant and much bet- ter known congener, the White-throated Crake (L. albigularis). To facilitate detection and iden- I Received 2 1 September 1987. Final acceptance25 tification of L. exilis. we also describe in detail March 1988. some vocalizations of L. albigularis.

I60171 608 F. G. STILES AND D. J. LEVEY

TABLE 1. Number of individuals of two Laterallus specieslocated by vocalizationson two censusesof different habitats at La Selva.

Wet season (August 198 I) Dry season (February 1983) L. exih L. albigularis L. exilis L. albigularis Habitat (n) (a (n) (n)

Tall grass-riverbank 0 3 0 4

TallShort-grass grass-highpasture ground 48+ ; 150 : Temporary marsh : : 4 1 Permanent marsh 0 10+ Totals 12+ 19 19 20+

HABITAT AND NEST repeatedly in searchof L. exilis.We twice flushed The first evidence of L. exilisin Costa Rica was Gray-breasted Crakes in a nearby pasture. Even- obtained at the La Selva Biological Station, 3 km tually we learned their call and how to distinguish south of Puerto Viejo de Sarapiqui, Provincia de it from those of the abundant L. albigularis.This Heredia, in the Caribbean lowlands, by S. Arm- permitted us to conduct a rough census of the bruster, M. Grayum, and P. Werner. At about two speciesin the area, a mosaic of tall grasson 22:00 on 5 February 1980, a bird flew into the high ground and along the river, shorter grassin field station where, evidently blinded by the lights, pastures, and both temporary and permanent it was captured, examined in detail with refer- marshes (Table 1, Fig. 1). ence to a field guide, identified as L. exilis,and We regularly heard at least two L. exilisin one released (M. Grayum, in litt.). small (ca. 2 mZ) area of tall grassduring late July, The first indication of the habitat of L. exilis but all attempts to trap, glimpse, or flush them in the area was a bird observed by Levey at close failed. The birds were no longer present on 18 range on the dark, rainy afternoon of 24 July August and Stiles searched this dense patch of 198 1, as it foraged by a mud puddle on a dirt grass.He found a globular nest of (now) dry grass road through tall grass.Between 28 July and 18 stemsand blades, about 14 cm outside diameter. August 198 1, we traversed the surrounding area It had a wide side entrance and was located about

Aug 1981 (wet season)

Feb 1983 (dry season)

FIGURE 1. Schematic diagram. habitats in La Selva area: North bank of Rio Puerto Viejo with relative abundancesof two speciesof Laterallus in wet and dry seasons. GRAY-BREASTED CRAKE IN COSTA RICA 609

TABLE 2. Measurementsof Laterallus exilis.

Exposedculmen ’ Wing chord Tarsuslength Weight (mm) (mm) (mm) (9) Males 16.2 12.6 22.7 292 (15-18) (68-78) (21-25) Females 14.8 72.8 22.6 342.3 (14-16) (71-75) (22-23) Specimen:adult female (UCR 2684) 16.1 70.2 22.0 34.9 Released:adult, male? 15.6 69.0 23.0 31.0 ’ Measurementsfrom Blake 1977 (n = 19 males,6 females). 2 Weightsfrom Ripley 1977 (n = 7 males,3 females). ’ R. W. Storer(pen. comm.) reportsa weght of 27 g for a femaleL. exilis collectedin Paraguay.

10 cm above ground. Apparently abandoned due eliminate the runways and making much noise. to our disturbance of the birds 2 weeks earlier, By gradually decreasingthe radius of the semi- the empty nest disintegrated upon being re- circle, we drove the birds toward the net and moved from the grass.The structure of the nest captured two of them. One was photographed, agreesfairly well with the description by Belcher measured, and released, the other, an adult fe- and Smooker (1935) although L. albigularis male, was collected (no. 2684 in the bird collec- builds a similar nest (Wetmore 1965). tion of the Museo de Zoologia, Universidad de Costa Rica). This bird had very light fat, and its DESCRIPTION OF SPECIMENS stomach contained insect remains, including a On 22 February 1983 we set a line of mist nets 2-cm tettigoniid grasshopper.Ripley (1977) re- (anchored at the bottom) just in front of a drain- ports its diet as “mainly seedsand, to some ex- age ditch and adjacent to an area where we had tent, insects.” Measurements of our two speci- heard L. exilis calling. With three assistants,we mens agreewell with those given in Blake (1977) moved in a semicircular path in front of the net, (Table 2). Becausethe two birds were netted to- trampling the grassas thoroughly as possible to gether, it is likely they were a pair. Weight and wing length of the bird we released relative to the bird we collected, suggestthat the released bird was a male. The two were similar in plumage and soft parts, save that the bird releasedshowed some narrow white tipping on the wing coverts, while the specimen shows none. No previous description or illustration (e.g., Ripley 1977, Storer 1981) does justice to the colors of the bill of L. exilis. The distal third of the lower mandible was black, the rest was a pale, almost luminous green. The green extended onto the proximal quarter of the upper mandible, cre- ating a large, bright, sharply defined patch of color (Fig. 2). The conspicuous contrast of the green and black surely produces a striking effect in the dim light of the bird’s runways under dense grass. Further contrast is provided by the red irides and narrow bare yellow eyelids. The legs were yellowish-buff.

VOCALIZATIONS The commonest vocalization of L. exilis is an explosive series of two to 10 sharp, penetrating whistled notes (Fig. 3a). The first note is usually FIGURE 2. Laterallus exilis bill pattern. slightly higher in pitch than the following notes 610 F. G. STILES AND D. J. LEVEY

8 30

3b

/ / 1 I I I 1 ! I I ’ -1-l 0 2 4 3d 3e 1 1

” TIME IN SECONDS TIME IN SECONDS FIGURE 3. Sonogramsof Lateral/us exilis(a, b) and L. dbigdaris (c, d, e) vocalizations. (From Stiles, reel # 13 in Florida State Museum BioacousticalLaboratory and Archives.) GRAY-BREASTED CRAKE IN COSTA RICA 611

and is very abrupt. In longer series,the final notes TABLE 3. Responses of two Laterallusspecies to may drop slightly in pitch. This vocalization, playbacksof their own vocalizations, and those of the other species,May 1984. dudedededededede,is given in a variety of situ- ations: in alarm or excitement, in response to Stimuli playbacks, or in response to disturbances such Whistled call of Churring trill of as a loud noise. Often if one bird calls, others in L. exihs L. albigdaris (Fig. 3a) (Fig. 3~) the vicinity take up the chorus. Re- No re- Re- No re- There seems to be some confusion over this Species tested sp0lX SPOIX” SpXlSd Sp3IW+ vocalization of L. exilis and one of the Black L. exilis 4 2 1 2 Rail, L. jamaicensis. According to Ridgely (198 1), L. albigularis 3 2 8 0

a recording from central Panama ascribed to L. ’ Response = approach and/or vocalization (within 10 set of playing of call). jamaicensis by the recordist, S. T. Harty, may 2 No response = no vocalization within 10 set or approach. be from L. exilis. Stiles has heard the recording in question and is sure that it is of L. jamai- censis- we have never heard such a vocalization cal, reveal a notable change in habitat use be- from L. exilis. The vocalization of L. exilis is tween wet and dry periods (Fig. 1). Laterallus similar but contains many more notes and lacks albigularisalways occupiedthe permanent marsh a final rolling note (Reynard 1974). and riverbank, while L. exilis always occupied The second vocalization of L. exilis is a dry shorter grassin the pasture. However, in the wet rattle with a sharp, “ticking” quality (Fig. 3b). It seasontall grasson high ground was used mainly may be brief or fairly prolonged. We have heard by L. exilis and the temporary marsh by L. al- it mainly from birds at close range responding bigularis.In February this marsh had completely vigorouslyto playbacks,and occasionallyat dawn dried out and we found mostly L. exilis there, and dusk. We suspectit is a territorial song. In while all tall grasswas occupiedby L. albigularis. general, it is heard much less often than is the At this time, we found two pairs of L. exilis in more prolonged, bubbly, churring trill of L. al- an area 50 x 75 m in the pasture, and ca. seven bigularis (Fig. 3c), which is given in a wider va- to eight pairs in an area of ca. 2 ha. After 1984 riety of situations (more frequently in response the pasture was mostly abandoned and the grass to playback, disturbances like loud noises, etc.). grew higher. In June 1986, the grasswas mostly The trills of both speciescontain approximately over 1 m in height and occupied mainly by L. 20 syllables/set but they differ dramatically in albigularis. In February 1987 there were no L. harmonics. In L. albigularis the dominant fre- exilis in this area, but there were some in a more quency is approximately 1.5 kHz, with a strong intensively-cropped pasture 0.5 km to the north- harmonic at 3 kHz. In L. exilis each syllable east. contains three frequencies (ca. 1.8, 2.5, and 3.2 These results indicate that local habitat dis- kHz) at which the sound is almost equally in- tribution of the two Laterallus speciesis highly tense, suggestinga complex vibration of syringeal fluid, with L. albig-ularis generally occupying structures,but without harmonics (Fig. 3b). La- wetter sites.Moreover, individuals or pairs seem terallus albigularis also has a slurred chip note, spacedout and each speciesresponds to the oth- which it gives mainly when distressed,alarmed, er’s vocalizations (Table 3). This strongly sug- or excited (Fig. 3d); in intense alarm, a shrill geststhat the two speciesare interspecifically ter- squealis given (Fig. 3e). All of thesevocalizations ritorial, and that the habitat shifts might reflect can be readily distinguished from vocalizations competitive interactions. The fact that L. albi- of L. exilis, which permits the use of vocaliza- gularis seemed to respond more vigorously to tions to censusabundance and local distribution calls of L. exilis than vice versa suggeststhat the of the two species-a practical necessity as the former is the aggressivelydominant species,as birds are usually impossible to see. might be expected from its larger size (mean weight = 42.8 g, n = 8, Stiles, unpubl. data). In INTERACTIONS WITH LATERALLUS this respect, it is noteworthy that L. albigularis ALBIGULARIS used its churring trill freely in responding to play- Censuses of August 198 1 and February 1983 back of calls of both speciesbut L. exilis trilled (Table l), made within 1 hr of sunrise and/or only once when responding to calls of its own sunset, when these rails are most active and vo- species.It would be interesting to determine if 612 F. G. STILES AND D. J. LEVEY

L. exilis used its trill more freelv where L. al- Hardy and the Florida State Museum Bioacoustical bigularisare absent (e.g., Trinidad: ffrench 1973). Laboratoryand Archives for producingthe sonograms. D. Harrison drew the figures,and S. Russelland R. Storerimproved the manuscrintwith their comments. We also thank R. Storer for permission to use unpub- DISTRIBUTION lished data. D. L. was supported by a JessieS. Noyes Laterallus exilis appears to be quite widespread, Foundation Fellowship and a Chapman Award from and even locally common, in the wet lowlands the American Museum of Natural History. F.G.S. re- ceived support from the Viscerrectoria de Investiga- of Costa Rica. In July 1984 Stiles found it nu- cion, Universidad de Costa Rica. merous in wet pasturesand a small brushy marsh near Laurel and Comte, in the southern Pacific LITERATURE CITED lowlands of Provincia Puntarenas near the Pan- AMERKAN ORNITHOLOGISTSUNION.’ 1983. Check- ama border. In July 198 5 he heard it calling fre- list of North American birds. 6th ed. American quently in wet, marshy pasturesaround San Jose Ornithologists’ Union, Washington, DC. de Upala, Provincia Alajuela, near the Nicara- BELCHER,C., A&DG. D. SMOOKER.1935. Birds ofthe colonv of Trinidad and Tobaao. Part II. Ibis 57: guan border. In October 1985 he found it in sim- 279-297. ilar habitats near Puerto Viejo and Manzanillo, BLAKE,E. R. 1977. Manual of neotropical birds. Vol. Provincia Limon, in the extreme southeastern 1. Univ. of Chicago Press, Chicago, IL. Caribbean lowlands. With the deforestation of FFRENCH, R. 1973. A guide to the birds of Trinidad most of Costa Rica’s humid lowlands in the last and Tobago. Livingston Publishing Co., Wynne- wood, PA. L. exilis, 30 years, we believe that the habitat of HILTY, S. L., AND W. L. BROWN. 1986. A guide to and its total numbers, have increased greatly. the birds of Colombia. Princeton Univ. Press, However, there seems no reason for supposing Princeton, NJ. that this speciesis a recent invader of Costa Rica. HOWELL,T. R. 1957. Birds of a second-growthrain forest area of Nicaragua. Condor 59:73-l 11. It has probably been present, but overlooked, all MEYERDE SCHAUENSEE, R. 1966. The speciesofbirds along-scarcely surprising in view of its ex- of South America and their distribution. Living- tremely secretive, skulking behavior. We believe ston Publishing Co., Narberth, PA. that L. exilis will be found common elsewhere MILLER,A. H. 1960. Additional data on the distri- in Central America and that Olson’s statement bution of some Colombian birds. Nov. Colomb. 1:235-237. that “exilis is far lesscommon [in Central Amer- MONROE,B. L. 1968. A distributional survey of the ica] than in South America” (Olson 1974:172) birds of Honduras. Omithol. Monogr. No. 7, needs reevaluation (see also Meyer de Schauen- American Ornithologists’Union, Washington,DC. see 1966). NEGRET,A., AND D. M. TEIXEIRA. 1984. The Ocel- lated Crake (Micropygia schomburgki)of Central Several authors have reported finding two or Brazil. Condor 86:220. more speciesof Laterallus (and other small rails) OLSON,S. L. 1974. The Pleistocene rails of North to be locally sympatric, apparently with or with- America. Condor 76: 169-l 75. out segregationby habitat (Storer 1981, Negret REYNARD,G. B. 1974. Some vocalizations of Black, and Teixeira 1984, Teixeira and Mendez Pirga Yellow and Virginia rails. Auk 9 11747-756. RIDGELY,R. S. 1981. A guide to the birds of Panama. 1984, Hilty and Brown 1986). Our observations Princeton Univ. Press, Princeton, NJ. strongly suggestthat the coexistence of small RIPLEY.S. D. 1977. Rails of the world. D. E. Godline neotropical rails may be a highly dynamic pro- Co., Boston. cess, perhaps largely mediated by interspecific RUSSELL,S. M. 1966. Status of the and Grav-breastedCrake in British Honduras. Condor territoriality and/or aggression,and strongly af- 68:iO5-107. fected by seasonal and successionalchanges in STORER,R. W. 1981. The Rufous-faced Crake (La- water levels and vegetation. teral/usxenopterus) and its Paraguayancongeners. Wilson Bull. 93: 137-144. ACKNOWLEDGMENTS TEIXEIRA.D. M.. AND M. E. MENDEZPIRGA. 1984. Notes on the SpeckledCrake (Coturnicopsnotata) The Organization for Tropical Studies provided logis- in Brazil. Condor 86:342-343. tical support, E. Brennan and M. Eddison helped cap- WETMORE,A. 1965. Birds of the Republic of Panama. ture the rails, and G. B. Reynard kindly provided the Part I. Smithson. Misc. Collect. 150. recordingof L. jamaicensis.We especiallythank J. W.