Pandion haliaetus ridgwayi es una subespecie que nidifica en la cuenca del Caribe sobre la que se conoce muy poco. En este trabajo presentamos un panorama sobre el estatus y la distribución de esta subespecie, con énfasis en la delineación de áreas de concentración de nidificación y proporcionando notas breves sobre su historia natural. En general P. h. ridgwayi se distribuye de forma dispersa y en números limitados con nidificación documentada en el sur de las Islas Bahamas, Turks y Caicos, y a lo largo de las costas de Cuba, de Yucatán en México y de Belice. Las zonas costeras albergan las únicas parejas reproductivas conocidas, las que construyen sus nidos en una variedad de estructuras naturales y cada vez con mayor frecuencia en estructuras artificiales. La mayoría de las parejas ponen sus huevos en noviembre y diciembre y generalmente los pichones dejan el nido en febrero y marzo. Datos limitados sugieren que las tasas reproductivas son bajas comparadas con aquellas de individuos de P. haliaetus que nidifican en latitudes más templadas. Recomendamos esfuerzos renovados para el censado de esta especie, especialmente en regiones donde los nidos pueden estar agrupados y discutimos el potencial para incrementar las poblaciones clave con plataformas artificiales para la nidificación.
The Caribbean Osprey (Pandion haliaetus ridgwayi) is a nonmigratory Osprey that nests in scattered numbers across the northwestern Caribbean, from the Bahamas through Cuba to the Yucatan Peninsula and Belize. Distinguished from its North American counterpart (P. h. carolinensis) by paler plumage and a whiter head, this bird remains in many ways the least known and certainly the least studied of the world's four subspecies of Osprey. Given its apparent low numbers and restricted range, this bird may even be at risk.
We present here an overview of the status and distribution of this little-known bird, with a focus on delineating areas of nesting concentration; we also provide brief notes on natural history as well as directions for future research. Because little is known, we base much of this report on a study of museum specimens, but include published and unpublished field reports, where available, as well as notes from a preliminary study of a small colony of Ospreys nesting in southern Belize.
Wink et al. (2004) recommended elevation of the four recognized Osprey subspecies (P. h. haliaetus, carolinensis, ridgwayi, and cristatus) to species level. That study, however, was limited to the calculated genetic distance of a single mtDNA gene (cytochrome b), and included no molecular data from ridgwayi, so we regard these conclusions as premature. See Prevost (1983) for a detailed discussion of Osprey subspecific taxonomy.
Data from museum collections were gathered from specimen labels during visits to institutions. JWW's work in Cuba was conducted incidental to other research in Isla de Pinos from 1992 to 2006, and in Ciénaga de Zapata from 2007 through 2012. JWW's observations in Cuba were facilitated by the Empresa Nacional para la Conservacion de la Flora y la Fauna, and he accompanied Empresa biologists on aerial surveys of Ciénaga de Zapata and Isla de Pinos. He was provided transportation to Ospreys nesting on cays by local fishermen at Playa Larga, Ciénaga de Zapata, and western Isla de Pinos. Field data were collected during brief, irregular visits to nest sites.
We derived information about ridgwayi in Belize and the Yucatan from varied sources: Sprunt's (1977) aerial surveys in April–May of 1971; brief, irregular, incidental observations by AFP, February 1988–2005, while traveling by boat and flying aerial surveys (1989, Belize coast only) in the region; and a more focused study at Glover's Reef Atoll, southern Belize, by NJC (under the auspices of the Wildlife Conservation Society), 18–23 January and 13–22 November 2008. This latter study involved surveys of nest activity, the establishment of a monitoring network, and nest observations (45 h total at three nests, dawn to dusk) with a focus on diet, foraging activity, and breeding behavior and nest success.
Results and Discussion
The Caribbean Osprey occurs in the Bahamas, the Turks and Caicos Islands, and Cuba (offshore cays and coastal regions), where it appears to be generally a rare resident, common in only a few locations. Among the 62 specimens of Ospreys JWW located in 23 museum collections in the West Indies, North America, and Europe, P. h. ridgwayi (n = 26) had been collected only in the Bahama Islands, the Turks and Caicos Islands, and Cuba and its satellites (Appendix; Fig. 1).
Elsewhere in the West Indies, no thorough survey or study of Ospreys has yet been conducted, so almost all information on P. h. ridgwayi has come through incidental observations. Interpreting these data is often difficult because North American Ospreys (P. h. carolinensis) migrate through and winter (a few) in the Bahamas and Antilles, and the majority of Osprey reports from the islands do not distinguish between the races. Further, some carolinensis are known to over-summer in the islands, and are often assumed by observers to be ridgwayi. Even where nesting has been reported, most observers have not recorded the race of the breeding birds, assuming all were ridgwayi. In recent years, however, several reports of carolinensis breeding in Cuba (see below) have complicated the description of the breeding range of ridgwayi.
Pandion h. ridgwayi is a vagrant to Hispaniola (Latta et al. 2006), the Cayman Islands (Bradley 1995, 2000), and possibly the Virgin Islands. Historically, it has been suggested that this race bred in the British Virgin Islands (George Dog, Anegada; Nichols 1943, Mirecki et al. 1977; but see Robertson 1962, Wiley 1984, Norton et al. 1989). One unlikely breeding record exists for St. Lucia in the Lesser Antilles (Keith 1997). Questionable records exist for breeding in Jamaica (e.g., Gosse in Gundlach 1876, 1893, Tenison 1968); these reports, however, are atypical, as all others report Ospreys have not nested in Jamaica, despite some birds over-summering on the island (e.g., Fletcher and Downer 1984, Swabey 1990). Furse (2005) reported both carolinensis and ridgwayi in coastal Grenada in December.
Ospreys have been observed constructing rudimentary nests (and old nest structures have been reported) in the Dominican Republic (Dod 1981, Wiley and Ottenwalder 1990, Latta et al. 2006, J. Brocca pers. comm.), Puerto Rico (Pérez-Rivera and Bonilla 1980, McNair et al. 2006, R. Pérez-Rivera pers. comm., J. Wiley unpubl. data) and St. Croix, U.S. Virgin Islands (Nellis 1979, Norton et al. 1989). No evidence of eggs or nestlings has been presented for any of these locations, however, nor have any of the building birds been identified as ridgwayi. Several of the birds observed constructing nests in Puerto Rico and the Virgin Islands were likely juvenile carolinensis (Norton 1989).
In the Bahamas, the Osprey is a widespread and fairly common resident, breeding sparingly on islands south of the Northeast Providence Channel (ca. 26°N, 77°W; Buden 1979, White 1998; Table 1). On Eleuthera, field crews active in the period 2002 to 2010 recorded only two nesting locations along the coast from Governor's Harbor south to Cape Eleuthera (J. Wunderle pers. comm.). Breeding has not been recorded in the northern Bahamas, on islands north of New Providence. Brudenell-Bruce (1975) suggested that many Osprey records for New Providence pertain to the migratory carolinensis. In summary, we find no records of concentrated breeding anywhere in the Bahamas, no cays or groups of cays where nests appear to be clustered (>2–3 nests).
Breeding records of Osprey (Pandion haliaetus ridgwayi) in the Bahamas and Turks and Caicos Islands.
Pandion h. ridgwayi is a widespread and permanent breeding resident throughout the Turks and Caicos Islands (Buden 1979, Ground 2001, Hallett 2006; Table 1). Although data are sparse, the bird appears to be fairly common here; indeed, if there is any nesting concentration in the West Indies, it appears to be in the Turks and Caicos. Future surveys would do well to focus on these islands.
Pandion h. ridgwayi has been reported from many of Cuba's 4195 satellite islands and several coastal areas of mainland Cuba, particularly Ciénaga de Zapata, Ciénaga de Birama, and the southern coast of Guantánamo (e.g., Gundlach 1876, 1893, Bond 1950a, 1956, Garrido and García Montaña 1975, Wotzkow 1985; Table 2; Fig. 1). P. h. ridgwayi is associated with cays, coastal bays, and saltwater areas, but also has been reported from coastal lakes and river mouths (Gundlach 1876, 1893, Wotzkow 1985; C. Wotzkow pers. comm.). Although the migratory race (P. h. carolinensis) is also encountered in saltwater lagoons and mangroves on the coasts and cays of Cuba (Garrido and García Montaña 1975), it is more often associated with inland freshwater bodies, including reservoirs, canals, rivers, temporary water bodies, and rice fields (Wotzkow 1985, C. Wotzkow pers. comm., O. Garrido pers. comm.). Both races occur in the Ciénaga de Zapata, but ridgwayi is the prevalent subspecies (J. Wiley unpubl. data).
Localities where Osprey (Pandion haliaetus ridgwayi) has been recorded in Cuba, Isla de Pinos, and satellites. Breeding records are indicated by “*.”
Although González Alonso (2002) reported Pandion h. ridgwayi as a locally abundant or common resident, most observers have considered it a rare permanent resident in Cuba, except in Oriente, where it appears to be more common (Garrido and García Montaña 1975, Wotzkow 1985). Kirkconnell (pers. comm.) noted that in the past the distribution of ridgwayi was much wider in the south. At Isla de Pinos (now Isla de la Juventud), Todd (1916) considered this bird a rare visitor, although it is now considered a common resident (J. Wiley unpubl. data). Pandion h. ridgwayi also breeds in the mangroves of Ciénaga de Zapata and on Cuba's offshore cays, including the archipelagos of Los Colorados, Sabana-Camagüey, Los Jardines de la Reina, and Los Canarreos (Table 3).
Timing of nesting activities of Osprey (Pandion haliaetus ridgwayi) in the Bahamas and Turks and Caicos Islands.
We note that although ridgwayi is known to breed in these locales, there are no data on overall numbers, or on areas where nesting may be concentrated; nor do we have much information on breeding success. Possible areas of concentration, in addition to Oriente, include Isla de Pinos, Los Jardines de la Reina, and the Los Canarreos, Los Colorados, and Sabana-Camagüey archipelagos, but researcher access is limited in all these areas, particularly to aircraft. There is a clear need for surveys during peak nesting season in these locations.
The migratory race carolinensis has long been considered a common winter resident and fall/spring transient in Cuba (Garrido and García Montaña 1975, Wotzkow 1985, Kirkconnell and Garrido 1991, 1997), but in recent decades this subspecies has become even more common. Wotzkow (1985) noted that the number of migrant and summer resident carolinensis increased since the middle of the 20th century. The increased number of carolinensis Ospreys visiting and remaining in Cuba year-round suggests that this race is encountering changing ecological conditions in Cuba that favor it. Since the end of the 1960s, aquatic habitats have increased substantially in Cuba with the construction of dams and creation of reservoirs, as well as expansion of the rice industry (Garrido and Wotzkow 1990). Also, substantial introductions of exotic fishes (including Oreochromis aureus, Sarotherodon mossambicus, Tilapia melanopleura, Micropterus salmoides; A. Pérez pers. comm.) have been made in recent years. As a consequence of additional and improved habitat, with augmented food supplies, populations of many bird species, including carolinensis Osprey, have increased in number and distribution in Cuba. Further, populations of North American Osprey have recovered from pesticide-related declines in the 20th century, so there are more individuals migrating through Cuba since that recovery. Satellite-tracking data suggest that at least 80–90% of North American Ospreys breeding east of the Mississippi River migrate through Cuba (see http://www.ospreytrax.com/2013AdPTT.html# for routes flown by Ospreys breeding in the northeastern U.S.).
Breeding by carolinensis in Cuba has been recorded in recent years, with numbers apparently increasing (Kirkconnell and Garrido 1991, 1997). C. Wotzkow and O. Garrido (pers. comm.) observed that P. h. carolinensis has recently occupied regions of Cuba that were formerly inhabited only by ridgwayi, with the latter race diminishing in numbers there.
There have been reports of mixed (ridgwayi × carolinensis) pairs of Ospreys reproducing in Cuba in recent years (Wotzkow 1985, Garrido 1992). Wotzkow (1985) reported a mixed pairing of the subspecies on Cayo La Piedra (Cayo Farito; northwest of Cayo Largo), where the pair nested in 1981. Bond (1956) noted that specimens of ridgwayi from the cays off southern Cuba had darker plumage, similar to that of carolinensis. That similarity may reflect hybridization between the two races. On the other hand, such similarity could compromise distinction of carolinensis from ridgwayi individuals by field observers, thus resulting in misidentification of individuals in pairs.
The only published survey of nesting Ospreys in this region was carried out by Sprunt (1977), who flew the Gulf and Caribbean coasts of Mexico, and the cays of Belize, in late April and early May, 1971. His flights focused on censusing colonies of nesting herons and egrets, but he noted Ospreys and their nests in passing. April and May are late to be censusing Ospreys in this region, as many pairs have fledged young (or failed) and left nests by then. In addition, reliably distinguishing individual ridgwayi from carolinensis at an altitude of 60–100 m is difficult; nests, however, are generally conspicuous from the air, so we focus here on Sprunt's counts of Osprey nests, with or without Ospreys in residence.
Along the Yucatan coast, Sprunt found Osprey nests in the Bahía de la Ascensión (Ascension Bay, part of the Sian Ka'An Biosphere Reserve: nine nests) and the Bahía del Espírito Santo (five nests). He found only one or two other nests outside this region in Caribbean Mexico. Ospreys and their nests were more common in Belize, where Sprunt found six nests scattered along the coast and cays north of Belize City, and 10 to the south; by far the largest concentration, however, was on the Turneffe Islands, a ca. 40 km2 atoll off the coast of northern Belize where Sprunt counted 17 nests. His survey did not include the atolls at Lighthouse or Glover's reefs, Belize, however, which are now known Osprey nesting sites (see below).
Surprisingly, no one has published reports of breeding Ospreys in Belize or the Yucatan since this survey, although recent anecdotal evidence suggests that ridgwayi has increased along the Yucatan coast and (perhaps) decreased in Belize. AFP (unpubl. data) found ridgwayi Ospreys fairly common (5–8 birds/d) along eastern edges of the Sian Ka'An Biosphere Reserve in February 2006 and 2007, with local eco-guides reporting 6–8 active nests within ca. 5 km of their lodge (ca. 15 km south of Tulum). Along the coast of Belize, AFP (unpubl. data, 1995–2005) found only scattered nests (3–5 active) on cays south of South Water/Carrie Bow, excluding Glovers Reef (see below). North along the Belize Barrier Reef, Ospreys have been known to nest in recent years (2010–2014) on Lighthouse Reef (one nest on Half Moon Caye, one on Long Caye), on Caye Caulker (one nest), on Ambergris Caye (one or two nests; A. Poole unpubl. data), and on Tobacco Caye (one nest; C. Dykstra unpubl. data). Although there are reports of other nests scattered throughout the northern cays, none has been substantiated. Clearly, renewed survey work is needed in this region, particularly on the Turneffe Islands where Sprunt (1977) found nesting concentrations in 1971.
Further south along the coast of Belize, on Glover's Reef Atoll, NJC (2008a, 2008b) found six active nests in January 2008, with a total of 18 ridgwayi in residence along a stretch of cays and reef about 6 km in length, indicating 12 breeders and 6 nonbreeders. Later that year, at the start of the breeding season (13–22 November), she located 4–5 active nests, although the total number of birds remained roughly the same, with five of the nonbreeders known juveniles.
Although data on movements of P. h. ridgwayi are few, it is generally considered a nonmigratory bird, based on year-round observations at nest sites (Poole 1989). Nonetheless, some researchers suggested that some portions of Cuban ridgwayi populations may be migratory, or at least show local movements outside of the breeding season (C. Wotzkow and O. Garrido pers. comm.). Gundlach (1893) was the first to observe seasonal migration of Ospreys along the coast of Guantánamo. Although he did not know of the two subspecies, ridgwayi is particularly abundant in this zone and is likely the race to which Gundlach referred (Garrido and García Montaña 1975, A. Llanes pers. comm.).
Clum (2008a) provides details from 45 hr of observation at three nests on Glover's Reef, November 2008. Key findings included: (1) duration of male foraging trips was short, averaging about 20 min, with 6 of 13 trips <10 min; (2) length of fish delivered to nests ranged from 15 to 30 cm, with estimated mass of those fish 150–350 g; (3) 1–4 fish/d were delivered to nests, adequate to meet estimated energy requirements of both the foraging male and his mate during incubation, when these observations took place, and roughly equivalent to prey delivery rates at Osprey nests in the U.S.A. (Poole 1989); and (4) genera of key identifiable prey species were Mulloidichthys, Ocyurus, Acanthurus, among others. In conclusion, during the period of this study, ridgwayi at Glover's Atoll did not appear to be food-limited. Clearly, we need further studies of additional populations at other times of year, particularly during the nestling season and during windy and stormy weather.
Pandion h. ridgwayi in Cuba characteristically builds its nest close to the sea on a prominent point of land, in the top of red (Rhizophora mangle), black (Avicennia germinans), or buttonwood (Conocarpus erectus) mangroves, or on the ground, rocks, or human-made structures (lighthouses, buoys, or partially or totally inactive cranes; Valdés Miró 1984, Wotzkow 1985, O. Suárez pers. comm., J. Wiley unpubl. data). Of seven active nests examined by Wiley, five were in red mangrove trees, two were in black mangroves; of 16 inactive nests, 11 were in red mangroves, three were in black mangroves, one was in a buttonwood mangrove, and one was on the ground. Mean height of active ridgwayi nests measured by JWW was 3.1 m (n = 7; range = 2–4 m).
Ospreys in the Bahamas nest on the ground, on sea-stacks, or in trees in isolated areas (Paterson 1972, E. Haxby in Norton 1985, J. Kushlan pers. comm.). Among human-made structures used by nesting Ospreys were an old pier, an abandoned church roof, and a field station water tower (White 1998). Paterson (1972) noted that pairs often use the same nest in successive seasons, adding to it each year.
In Belize, ridgwayi is known to nest on lighthouses, on the roofs of fishermen's shacks, on logs washed up along reefs, in trees (mostly mangrove), and on artificial platforms (Clum 2008b, A. Poole unpubl. data). We note that all nests found in Belize have been on offshore cays—along the reef and on atolls outside the reef; we found no records of nests along the mainland coast of Belize, perhaps owing to the threat of increased predation (snakes, iguanas) in that environment. Clum (2008b) detailed the locations of six nests found in January 2008 on Glover's Reef Atoll: two on artificial structures (lighthouse, tripod); three on the roots of overturned trees washed up along the reef; and one in a live white mangrove. This study suggested that nest sites are limited for Ospreys on Glover's Reef (very few trees and logs provide adequate support), but that the potential for bolstering populations with artificial nest sites (tripods, platforms) is considerable. Given the extraordinary degree to which carolinensis Ospreys use artificial nest sites in the U.S.A. (Poole et al. 2002), we encourage a program to develop nesting platforms for ridgwayi on the cays of Belize.
Along the Yucatan coast, ridgwayi nests in low trees on small islets, and occasionally on taller, flat-topped mangroves on larger cays (Sian Ka'An Biosphere Reserve; A. Poole unpubl. data). Increasingly, Yucatan Ospreys are nesting on artificial structures; e.g., a successful nest on a communications tower along the coast south of Tulum, and attempted nests (generally unsuccessful because support is lacking) on small thatched residences along that same coast (A. Poole unpubl. data). Here again, the potential to develop artificial sites to support Osprey nests seems considerable, especially considering that these could provide wildlife attractions in an area where ecotourism dominates the economy.
Nesting activity in the Bahamas and Turks and Caicos Islands generally spans a period from mid-October through April (Table 3), although there is a record of a pair on a nest as early as 10 September (Inagua Site Support Group in Norton et al. 2005) and a nest with an egg (likely inviable) as late as 11 April (D. Campbell in Buden 1979).
Breeding in Cuba follows a similar pattern, usually from October to May (A. Kirkconnell pers. comm.). Garrido (pers. comm.) observed an Osprey carrying a large stick on 25 February 1986. Nests at Los Indios, Isla de Pinos, contained eggs 10–18 December 1995 (three nests), and 24–26 December 1996 (three nests; J. Wiley unpubl. data). Three nests observed in Ciénaga de Zapata, 2–8 February 1999, contained half-grown nestlings (J. Wiley unpubl. data).
On Glover's Atoll, Belize, females produced eggs from mid-November to mid-January, with most birds laying mid-November to mid-December (Clum 2008b). Thus, most nestlings hatched during January, fledging in February and March.
Overall, the breeding season in Caribbean ridgwayi (peak egg-laying November–December; peak period for nestlings January–March) seems roughly similar to that seen in Osprey (P. h. carolinensis) populations in southern Florida, but significantly longer (at least 2 mo longer) than the laying period for northern U.S. Ospreys (carolinensis), where egg-laying is restricted to a period from early April to mid-May (Poole 1982, 1989). One would predict a more relaxed nesting period for ridgwayi, given the lack of pronounced seasonality and of significant migration in this race.
Ospreys generally lay 2–3 eggs in Cuba (Gundlach 1893, Garrido 1992). JWW found a mean of 2.7 (range = 2–3) eggs per clutch at seven nests in Cuba (J. Wiley unpubl. data). In the Bahamas, clutches ranged from one to three eggs (D. Campbell in Buden 1979, Wolfe 1951). Six sets of ridgwayi eggs (in the Ragnar Kreuger collection of the Finnish Museum of Natural History, University of Helsinki) collected from 1925 to 1935 at Andros Island, Bahamas averaged 2.66 (ranges = 2–3). Such clutch sizes are lower than those of Ospreys nesting at temperate latitudes in the U.S.A. and Europe, but equivalent to those of Ospreys nesting at subtropical latitudes (e.g., Florida Bay, Baja California; Poole 1989).
Brood size and fledging success.
We find few data on breeding success in this subspecies; unlike with Ospreys breeding in the U.S.A., no study has followed a population from egg-stage to fledging, to determine extent of loss, at what stage of nesting loss occurs, and overall success. Instead, we report here data from occasional (generally single) observations at scattered nests.
One nest in the Bahamas had two young (R. Sutherland in Buden and Sprunt 1993). The Inagua Site Support Group (in Norton et al. 2005) reported two pairs with two fledglings each, and four pairs with one fledgling on Great Inagua. Six nests examined in Cuba contained from one to three nestlings each (ages not reported; C. Wotzkow pers. comm.). Three nests observed at Ciénaga de Zapata (two nests) and Isla de Pinos (one nest) contained two nestlings each (J. Wiley unpubl. data). Both young fledged from one intensively studied nest (Wotzkow 1985).
In Belize (Clum 2008b), the duration of the Glover's Reef study was too short to determine fledging success (and clutch size) accurately, but in mid-January four surveyed nests contained: two small nestlings, one egg, one egg, and two eggs. Of two nests with adults surveyed briefly in the Sian Ka'An Biosphere Reserve, February 2007, one had 0 young and one had two young near fledging (A. Poole unpubl. data).
Overall, although data are sparse, brood sizes of ridgwayi Ospreys near fledging appear roughly similar to those of carolinensis Ospreys breeding at subtropical latitudes (south Florida and Baja California; Poole 1989, Poole at al. 2002). Clearly, we need better data on ridgwayi breeding success, from focused studies that follow nests over an entire season. Areas of nesting concentration—such as Glover's Atoll, Belize; Great Inagua, Bahamas; the Turks and Caicos Islands; and the Sian Ka'An Biosphere Reserve—would be obvious places to start. We encourage such studies.
For providing unpublished data, we thank Ancilleno O. Davis, James Kushlan, Rosemarie S. Gnam (Bahamas); Pedro Blanco, Orlando H. Garrido, Arturo Kirkconnell, Orestes Martínez, José “Fefo” Morales, Nils Navarro, Carlos Peña, Freddy Rodríguez Santana, Ariel Ruiz Urquiola, Bárbara Sánchez, Carlos Wotzkow (Cuba); Patrica E. Bradley (Cayman Islands and Turks and Caicos Islands); Ann Haynes-Sutton (Jamaica); Marcia Beltre, Jorge Luis Brocca, José A. Ottenwalder (Dominican Republic); Wayne J. Arendt, Sergio Colón, Raúl A. Pérez-Rivera, Fred C. Schaffner Gibbs (Puerto Rico); Judy Pierce, Lisa Yntema (Virgin Islands); Anthony Levesque (Guadeloupe); Alwin Dornelly (St. Lucia); Natalia Collier (Lesser Antilles); and J. Wunderle (Puerto Rico and Bahamas). JWW's work in Cuba was supported by the Empresa Nacional para la Conservación de la Flora y la Fauna; Centro para Investigaciones Marinas, Universidad de La Habana; and Museo Nacional de Historia Natural de Cuba. JWW is especially grateful for the support and companionship of Ariel Ruiz, the late María Elena Ibarra, Arturo Kirkconnell, Emilio Alfaro, Xiomara Gálvez Aguilera, and José Rivera Rosales. We thank the many curators and collection managers who provided data and accommodations during our visits to their institutions. Among these, we especially thank Steven W. Cardiff. Lynda Garrett (Patuxent Wildlife Research Center) and Robert L. Norton generously helped in obtaining literature. Thanks to Brooke Keeney for producing the map.