Puerto Rican Parrot Research Articles

Avian studies and research opportunities in the Luquillo Experimental Forest: A tropical rain forest in Puerto Rico

The Luquillo Experimental Forest (LEF) located on the Caribbean island of Puerto Rico has a rich history of ecological research, including a variety of avian studies, and is one of the most active ecological research sites in the Neotropics. The LEF spans an elevational range from 100 to 1075 m over which five life zones and four forest types are found in a warm, humid subtropical climate. A total of 23 bird species breeds here and another 76 species, mostly migrants, are known to occur. The food web of the forest in the lower elevations is especially well studied, which allows an assessment of the role of birds in the food web. The LEF is noted for its high densities of Eleutherodactylus frogs and Anolis lizards, which may depress insect densities thereby contributing to the low species richness and densities of most insectivorous birds. The signature species of the forest is the endangered Puerto Rican Parrot ( Amazona vittata) that has been the focus of intensive long-term research and recovery efforts, which have spawned research on associated species, including long-term studies on the Pearly-eyed Thrasher ( Margarops fuscatus) and botfly ( Philornis spp.) ectoparasitism. Given the frequency of hurricane disturbance to the LEF and studies providing baseline for comparisons, research has made major contributions to an understanding of the effects of hurricanes on forest ecosystems including bird populations and their resources. We summarize these and other studies from the LEF to characterize the avifauna and its environment while noting studies with management implications and identify opportunities for future ornithological studies.

ANATOMY OF A BOTTLENECK: DIAGNOSING FACTORS LIMITING POPULATION GROWTH IN THE PUERTO RICAN PARROT

The relative importance of genetic, demographic, environmental, and catastrophic processes that maintain population bottlenecks has received little consideration. We evaluate the role of these factors in maintaining the Puerto Rican Parrot (Amazona vittata) in a prolonged bottleneck from 1973 through 2000 despite intensive conservation efforts. We first conduct a risk analysis, then examine evidence for the importance of specific processes maintaining the bottleneck using the multiple competing hypotheses approach, and finally integrate these results through a sensitivity analysis of a demographic model using life‐stage simulation analysis (LSA) to determine the relative importance of genetic, demographic, environmental, and catastrophic processes on population growth. Annual population growth has been slow and variable (1.0 ± 5.2 parrots per year, or an average λ = 1.05 ± 0.19) from 16 parrots (1973) to a high of 40–42 birds (1997–1998). A risk analysis based on population prediction intervals (PPI) indicates great risk and large uncertainty, with a range of 22–83 birds in the 90% PPI only five years into the future. Four primary factors (reduced hatching success due to inbreeding, failure of adults to nest, nest failure due to nongenetic causes, and reduced survival of adults and juveniles) were responsible for maintaining the bottleneck. Egg‐hatchability rates were low (70.6% per egg and 76.8% per pair), and hatchability increased after mate changes, suggesting inbreeding effects. Only an average of 34% of the population nested annually, which was well below the percentage of adults that should have reached an age of first breeding (41–56%). This chronic failure to nest appears to have been caused primarily by environmental and/or behavioral factors, and not by nest‐site scarcity or a skewed sex ratio. Nest failure rates from nongenetic causes (i.e., predation, parasitism, and wet cavities) were low (29%) due to active management (protecting nests and fostering captive young into wild nests), diminishing the importance of nest failure as a limiting factor. Annual survival has been periodically reduced by catastrophes (hurricanes), which have greatly constrained population growth, but survival rates were high under non‐catastrophic conditions. Although the importance of factors maintaining the Puerto Rican Parrot bottleneck varied throughout the 30‐year period of study, we determined their long‐term influence using LSA simulations to correlate variation in demographic rates with variation in population growth (λ). The bottleneck appears to have been maintained primarily by periodic catastrophes (hurricanes) that reduced adult survival, and secondarily by environmental and/or behavioral factors that resulted in a failure of many adults to nest. The influence of inbreeding through reduced hatching success played a much less significant role, even when additional effects of inbreeding on the production and mortality of young were incorporated into the LSA. Management actions needed to speed recovery include (1) continued nest guarding to minimize the effects of nest failure due to nongenetic causes; (2) creating a second population at another location on the island—a process that was recently initiated—to reduce the chance that hurricane strikes will cause extinction; and (3) determining the causes of the low percentage of breeders in the population and ameliorating them, which would have a large impact on population growth.

Using artificial canopy gaps to restore Puerto Rican Parrot ( Amazona vittata) habitat in tropical timber plantations

Timber plantations have the potential to catalyze regeneration of natural forest on degraded land. However, effective management methods to restore native tree diversity and wildlife habitat in areas planted with non-native timber species are needed. Our study investigated the effectiveness of creating artificial canopy gaps within timber plantations to increase germination, growth, and survival of native tree species that may be important food plants for the Puerto Rican Parrot ( Amazona vittata). Seedling growth increased significantly in gaps; however, there were no differences in percent germination or survival between gap and closed (control) plots. Percent cover of grasses, shrubs, and vines increased in gaps, but the increased growth of competitors did not prevent tree seedlings from growing significantly more rapidly in gaps. Removing leaf litter at time of sowing had no effect on germination, growth, or survival of direct seeded species. Creation of canopy gaps by girdling timber trees reduced basal area of non-native tree species to levels comparable with those of native trees. Both local and landscape level diversity were predicted to increase in canopy gaps; however, plantations will continue to be dominated by non-native and timber tree species because advance regeneration of these species is common in plantation understories. Our results suggest that restoration of native tree diversity and wildlife habitat in plantations will require continued management to remove non-native species and to promote growth of tree species with high wildlife habitat value.

Artificial nest cavities for Amazona parrots

Artificial nest cavities for Amazona parrots

SURVIVAL OF CAPTIVE-REARED PUERTO RICAN PARROTS RELEASED IN THE CARIBBEAN NATIONAL FOREST

We report first-year survival for 34 captive-reared Puerto Rican Parrots (Amazona vittata) released in the Caribbean National Forest, Puerto Rico between 2000 and 2002. The purpose of the releases were to increase population size and the potential number of breeding individuals of the sole extant wild population, and to refine release protocols for eventual reintroduction of a second wild population elsewhere on the island. After extensive prerelease training, we released 10 parrots in 2000, 16 parrots in 2001, and eight parrots in 2002 ranging in age from 1–4 years old. All birds were equipped with radio-transmitters to monitor survival. The overall first-year survival estimate for the 34 parrots was 41% (CI = 22%–61%). Only one parrot died within the first week postrelease, with most (94%) surviving for at least eight weeks after release. Most (54%) documented mortalities were due to raptor predation, which claimed 21% of all released parrots. A captive-reared bird (male, age one), released in 2001, paired with a wild female and fledged two young in 2004. We also calculated survival based on 0% and 50% of observed predation losses and found hypothetical survival rates of 72% and 54%, respectively. Rigorous prerelease training and acclimation was believed to have improved initial postrelease parrot survival, and releasing mixed age-class groups suggests the potential for shortening the time to recruitment. Supervivencia de Individuos de Amazona vittata Criados en Cautiverio y Liberados en el Bosque Nacional del Caribe Resumen. Determinamos la supervivencia de 34 individuos de cotorras Amazona vittata criados en cautiverio y liberados en el Bosque Nacional del Caribe, Puerto Rico entre el 2000 y el 2002. El propósito de las liberaciones era aumentar el tamaño de la población y el número potencial de individuos reproductores en la única población silvestre remanente, y refinar los protocolos de liberación para eventualmente establecer una segunda población silvestre en la isla. Después de un adiestramiento extensivo, liberamos 10 cotorras en el 2000, 16 cotorras en el 2001, y ocho cotorras en el 2002 fluctuando en edades entre uno y cuatro años. Cada individuo se liberó con un radio transmisor para determinar su supervivencia. La tasa general de supervivencia para 34 cotorras después de un año fue de 41% (IC = 22–61%). Sólo una cotorra murió durante la primera semana post-liberación, con la mayoría (94%) sobreviviendo por lo menos ocho semanas después de liberadas. La mayoría (54%) de la mortandad se debió a la depredación por aves rapaces, la que reclamó 21% de todas las cotorras liberadas. Una cotorra criada en cautiverio (macho, un año de edad), y liberada en el 2001, se apareó con una hembra silvestre y produjeron dos volantones en el 2004. Reduciendo la mortandad por aves rapaces informada en este estudio en un 100%, o en un 50%, resultó en tasas hipotéticas de supervivencia del 72% y 54%, respectivamente. Creemos que el adiestramiento y la aclimatación rigurosa pre-liberación mejoraron la supervivencia inicial post-liberación, y que la liberación de grupos de cotorras de edades mixtas sugiere el potencial de acortar el tiempo de reclutamiento.

ESTIMATING POPULATION TREND AND PROCESS VARIATION FOR PVA IN THE PRESENCE OF SAMPLING ERROR

Time series of population abundance estimates often are the only data available for evaluating the prospects for persistence of a species of concern. With such data, it is possible to perform a population viability analysis (PVA) with diffusion approximation methods using estimates of the mean population trend and the variance of the trend, the so-called process variation. Sampling error in the data, however, may bias estimators of process variation derived by simple methods. We develop a restricted maximum likelihood (REML)-based method for estimating trend, process variation, and sampling error from a single time series based on a discrete-time model of density-independent growth coupled with a model of the sampling process. Transformation of the data yields a conventional linear mixed model, in which the variance components are functions of the process variation and sampling error. Simulation results show essentially unbiased estimators of trend, process variation, and sampling error over a range of process variation/sampling error combinations. Example data analyses are provided for the Whooping Crane (Grus americana), grizzly bear (Ursus arctos horribilis), California Condor (Gymnogyps californianus), and Puerto Rican Parrot (Amazona vittata). This REML-based method is useful for PVA methods that depend on accurate estimation of process variation from time-series data.

An economic assessment of the potential for predator management to benefit Puerto Rican parrots

The Puerto Rican parrot is one of the ten most endangered birds in the world, with the only wild population comprised of 30–40 birds. Predation has been identified as one of the factors limiting Puerto Rican parrot productivity in the wild, and the loss of a very few birds can have a great impact on the species. Management of red-tailed hawks, and black rats, feral cats and Indian mongooses, as well as further management of pearly-eyed thrashers is potentially beneficial to the parrot population. Because funding for the recovery of this rare species is finite, an analytical examination of the economics of predator management as a species enhancement method can provide managers with a solid basis for justifying and implementing this management approach. We used a benefit–cost analysis (BCA) to examine the potential Pareto improvements of predator management for protecting Puerto Rican parrots. The median and minimum expenditures aimed at parrot reproduction for both captive and wild parrots from 1997 to 2001 were used to define monetary values for Puerto Rican parrots. Predator management costs were estimated from existing US Department of Agriculture/Wildlife Services (USDA/WS) contracts for similar work in Puerto Rico. We examined the benefit–cost ratios (BCRs) for predator management assuming one to five and ten parrots were saved by the efforts. Analyses were conducted separately for each predator species and all species combined. The primary analyses focused on the benefits and costs for predator management for the current wild parrot population in the Caribbean National Forest (CNF), but another set of analyses targeted the proposed Rio Abajo (RA) site for the establishment of a second wild population. This second set of analyses was more conservative than for the existing population because predator management costs were assumed to be higher. Even when using the minimum monetary valuation for Puerto Rican parrots, the prevention of a single mortality due to predation within the existing wild population results in monetary benefits slightly exceeding the combined costs for management of each predator species (BCR=1.01). If median parrot values are applied, then only one parrot saved every 2.6 years allows the combined predator management to be cost-effective. If the year of maximal parrot values (averaged over captive and wild populations) is used, then only one parrot saved every 4.2 years makes application of all predator management methods cost-effective. Use of the single highest per-parrot value from among years and populations would result in the combined application of all forms of predator management being cost-effective if only one parrot is preserved from predation every 11.8 years. Assuming higher costs and minimum parrot values results in the combined application of predator management at the RA proposed population site to be cost-effective if 1.8 parrots/year are saved from predation. Use of median parrot value allows predation management to be cost-effective if one parrot is saved every 1.4 years. If actual costs for the RA site are the same as for the CNF, then the BCRs improve correspondingly. As more parrots are saved, the BCRs increase dramatically for each site.

Ecorisk Assessment Using Indicators of Sustainability: Invasive Species in the Caribbean National Forest of Puerto Rico

Abstract Ecological risk assessment using indicators of sustainability offers a framework for the objective analysis of management decisions in complex landscapes. To demonstrate this approach, we examined risks to the Caribbean National Forest. Among the many stressors, invasive species (especially bamboo and Africanized bees) pose the largest potential risk to management goals. Although bamboo is spreading slowly, the risk of colonization is sufficient to require monitoring and research. Africanized bees, on the other hand, should be removed immediately from sensitive areas to increase the nesting success of the endemic but endangered Puerto Rican parrot.

Parrot conservation in the lesser antilles with some comparison to the Puerto Rican efforts

There are four endemic species of Amazona parrots in the Lesser Antilles, namely the imperial or Sisserou parrot Amazona imperialis and the red-necked or Jaco parrot A. arausiaca of the Commonwealth of Dominica, the St Lucia parrot A. versicolor of St Lucia, and the St Vincent parrot A. guildingii of St Vincent and The Grenadines. Seven other endemic members of the same family, Psittacidae, have become extinct in the region in historical times. These four extant species are now all threatened by deforestation, predation, illegal hunting and collecting, and natural disasters. Measures for parrot conservation consist of environmental education, habitat protection, enforcement of appropriate legislation, and enhancement of wild breeding and captive breeding. These approaches are reviewed for each of the islands and compared with the relatively successful but much more expensive conservation measures adopted for the Puerto Rican parrot A. vittata in the Commonwealth of Puerto Rico. Recommendations are made for future conservation emphasis and research.

Puerto Rican Parrots and Potential Limitations of the Metapopulation Approach to Species Conservation

Population viability analyses for a number of endangered species have incorporated a metapopulation approach. The risk assessments of these viability analyses have indicated that some extant populations should be subdivided into numerous subgroups with exchange of individuals among them in order to reduce the chance of catastrophic loss of the species. However, routine application of a policy of extensive subdivision may have detrimental consequences for certain endangered species. We examine the Puerto Rican Parrot as a case history in which this policy is ill‐advised. In 1989, apopulation viability analysis was conducted for the parrot. The document recommended subdivision of the existing small captive flock into three groups. One of these captive flocks would consist of individuals transferred to a multi‐species facility in the continental United States. Subsequently, individuals from this facility would be exchanged with the insular captive population(s) and the relict wild flock. For two reasons, implementation of this recommendation might have led to serious repercussions. First, this parrot, like many endangered species, has gone through a genetic bottleneck and may have a heightened susceptibility to disease. Multi‐species facilities are a high‐risk environment favoring the transmission of pathogens, especially when the facilities are located outside the natural ranges of a particular species. Second, the parrot is a K‐selected species for which mate selection is idiosyncratic. This type of species often proves difficult to breed in captivity in small groups. Part of the problem in mate selection may be reduced by a policy allowing frequent transfers of individuals among facilities, but such movements increase the chances of spreading disease in the metapopulation. Thus, population viability analyses need to acknowledge that proliferation of captive subgroups accompanied by exchanges of individuals can in themselves carry substantial risks that must be weighed against the presumed benefits of subdivision.

Fruit Fall in the Luquillo Experimental Forest, Puerto Rico

Fruit fall in the Luquillo Experimental Forest (LEF) varied with forest type but averaged 600 kg/ha/yr for the 11,000 ha forest. Within a given forest type, fruit fall varied spatially and seasonally. A palm (Prestoea montana) flood plain forest averaged 560 kg/ ha/yr and individual palm fruit mass changed from season to season. Lower montane wet, or tabonuco (Dacryodes excelsa ), forest had a low rate of fruit fall (332 kg/ha/yr) and strong seasonal pulses in both space and time. Fruit fall was higher in secondary forests (820 kg/ha/yr) and plantations (1418 kg/ ha/yr) than in mature tabonuco forests that normally occur in those sites. Fruit fall in the upper montane, or palo colorado (Cyrilla racemiflora), forest averaged 263 kg/ha/yr. Somewhere in the LEF there always appears to be a stand at peak rate of fruit production. Fruit fall data are used to reduce a previous estimate of forest carrying capacity for the endangered Puerto Rican parrot, Amazona vittata, from 51,000 to 2000-38,000 birds.

Application of DNA fingerprinting to the recovery program of the endangered Puerto Rican parrot.

The Puerto Rican parrot was reduced to approximately 13 animals in 1975 and as a conservation measure, a captive population was established from a few founders taken from the wild between 1973 and 1983. The number of successful breeding pairs in captivity has been low, and the captive breeding program has not been as productive as that of the closely related Hispaniolan parrot. Therefore, a genetic study was initiated to examine the relative levels of relatedness of the captive founders using levels of bandsharing in DNA fingerprints. Unrelated captive founder Puerto Rican parrots had the same average level of bandsharing (0.41) as second-degree relatives of the Hispaniolan parrot (0.38, P > 0.05), with an inbreeding coefficient of 0.04. High levels of bandsharing (> 40%) between pairs of males and females correlated with reproductive failure, suggesting that inbreeding depression is partly responsible for the low number of breeding pairs. Consequently, DNA profiling can be used to guide the captive breeding program for the Puerto Rican parrot, and other endangered species, by identifying pairs of males and females with low levels of bandsharing.

Characterization and assessment of an avian repetitive DNA sequence as an icterid phylogenetic marker.

The first tandemly repeated sequence examined in a passerine bird, a 431-bp PstI fragment named pMAT1, has been cloned from the genome of the brown-headed cowbird (Molothrus ater). The sequence represents about 5-10% of the genome (about 4 x 10(5) copies) and yields prominent ethidium bromide stained bands when genomic DNA cut with a variety of restriction enzymes is electrophoresed in agarose gels. A particularly striking ladder of fragments is apparent when the DNA is cut with HinfI, indicative of a tandem arrangement of the monomer. The cloned PstI monomer has been sequenced, revealing no internal repeated structure. There are sequences that hybridize with pMAT1 found in related nine-primaried oscines but not in more distantly related oscines, suboscines, or nonpasserine species. Little sequence similarity to tandemly repeated PstI cut sequences from the merlin (Falco columbarius), saurus crane (Grus antigone), or Puerto Rican parrot (Amazona vittata) or to HinfI digested sequence from the Toulouse goose (Anser anser) was detected. The isolated sequence was used as a probe to examine DNA samples of eight members of the tribe Icterini. This examination revealed phylogenetically informative characters. The repeat contains cutting sites from a number of restriction enzymes, which, if sufficiently polymorphic, would provide new phylogenetic characters. Sequences like these, conserved within a species, but variable between closely related species, may be very useful for phylogenetic studies of closely related taxa.

Status and conservation of parrots and parakeets in the Greater Antilles, Bahama Islands, and Cayman Islands

SummaryIn the 1490S a minimum of 28 species of psittacines occurred in the West Indies. Today, only 43% (12) of the species survive. All macaws and most parakeet species have been lost. Although the surviving parrot fauna of the Greater Antilles, Cayman Islands, and Bahama Islands has fared somewhat better than that of the Lesser Antilles, every species has undergone extensive reductions of populations and all but two have undergone extensive reductions in range, mostly as a result of habitat loss, but also from persecution as agricultural pests, conflicts with exotic species, harvesting for pets, and natural disasters. The Cayman Brae ParrotAmazona leucocephala hesterna, with its tiny population (lessthan 150 individuals in the wild) and range, and the Puerto Rican ParrotA. vittata, with 22-23 birds in the wild and 56 individuals in captivity, must be considered on the of extinction and in need of (in the tatter's case, continuing) aggressive programmes of research and management. Other populations declining in numbers and range include the Yellow-billedAmazona collaria, and Black-billedA. agilisParrots of Jamaica, Hispaniolan ParakeetAratinga chloroptera, Hispaniolan ParrotAmazona ventralis, Cuban ParrotA. leucocephala leucocephalaand, most seriously, Cuban ParakeetAratinga euops. The population of the Grand Cayman Parrot (Amazona leucocephala caymanensis), although numbering only about 1,000 birds, appears stable and the current conservation programme gives hope for the survival of the race. An active conservation and public education programme has begun for the Bahama ParrotA. l. bahamensis, which still occurs in good numbers on Great Inagua Island, but is threatened on Abaco Island. Recommendations for conservation of parrots and parakeets in the region include (1) instituting term programmes of research to determine distribution, status, and ecology of each species; (2) developing conservation programmes through education and management approaches that are culturally, politically, and economically sensitive to the region; and providing and protecting habitat within suitably sized reserves.

Estimation of Growth and Extinction Parameters for Endangered Species

Survival or extinction of an endangered species is inherently stochastic. We develop statistical methods for estimating quantities related to growth rates and extinction probabilities from time series data on the abundance of a single population. The statistical methods are based on a stochastic model of exponential growth arising from the biological theory of age— or stage—structured populations. The model incorporates the so—called environmental type of stochastic fluctuations and yields a lognormal probability distribution of population abundance. Calculation of maximum likelihood estimates of the two unknown parameters in this model reduces to performing a simple linear regression. We describe techniques for rigorously testing and evaluating whether the model fits a given data set. Various growth— and extinction—related quantities are functions of the two parameters, including the continuous rate of increase, the finite rate of increase, the geometric finite rate of increase, the probability of reaching a lower threshold population size, the mean, median, and most likely time of attaining the threshold, and the projected population size. Maximum likelihood estimates and minimum variance unbiased estimates of these quantities are described in detail. We provide example analyses of data on the Whooping Crane (Grus americana), grizzly bear (Ursus Arabis Hoffmann) in Yellow stone, Kirkland's Warbler (dealbatus killdeer), California Condor (Gymnoascus californianus), Puerto Rican Parrot (Amazona vicarius), pacificus (lobata bachei), and Layman Finch (tectorum cantons). The model results indicate a favorable outlook for the Whooping Crane, but long—term unfavorable prospects for the Yellow stone grizzly bear population and for Kirkland's Warbler. Results for the California Condor, in a retrospective analysis, indicate a virtual emergency existed in 1980. The analyses suggest that the Puerto Rican Parrot faces little risk of extinction from ordinary environmental fluctuations, provided intensive management efforts continue. However, the model does not account for the possibility of freak catastrophic events (hurricanes, fires, etc.), which are likely the most severe source of risk to the Puerto Rican Parrot, as shown by the recent decimation of this population by Hurricane Hugo. Model parameter estimates for the pacificus and the Layman Finch have wide uncertainty due to the extreme fluctuations in the population sizes of these species. In general, the model fits the example data sets well. We conclude that the model, and the associated statistical methods, can be useful for investigating various scientific and management questions concerning species preservation.

Home Range and Movements of Juvenile Puerto Rican Parrots

We studied home range and movements of 15 radio-marked, juvenile Puerto Rican parrots (Amazona vittata) fledging from wild nest during summer and fall, 1985-87. When juvenile parrots remained in the nest valley, home ranges during 1986 (x=32±10 [SE] ha, n=4) were larger (P=0.0079) than during 1987 (x=13±6 ha, n=5). After radio-marked parrots integrated into adult flocks, home ranges during 1986 (x=1,075±135 ha, n=3) were similar (P=0.10) to 1987 (x=416±62 ha, n=2). Juvenile marrots restricted their movements to nest valleys an average of 58±29 days following fledging. After joining adult flocks, juvenile parrots routinely flew between the east and west slopes of the Luquillo Mountains but did not exhibit a seasonal pattern of movement

A New Species of Warbler (Parulidae) from Puerto Rico

THE West Indies are among the best known of the world's tropical regions, and our knowledge of the distribution of indigenous land birds in the Greater Antilles has been thought to be nearly complete (Bond, 1956). The last new species from the Antilles were described in 19'27, the results of work in the Zapata Swamp of Cuba (Barbour and Peters, 1927) and the isolated Morne de la Selle in Haiti (Wetmore, 1927). No new species has been found in Puerto Rico in this century, and it would seem unlikely that a bird could escape detection on the island, which has a human population density now approaching 320 per square km, and less than 3,300 ha (0.4 percent of land area) of virgin forest remaining (Wadsworth, 1949). Nevertheless the discovery of extant populations of the Puerto Rican Whip-poor-will (Caprimulgus no.ctitherus) by Reynard (1962) and the Puerto Rican Plain Pigeon (Columba inornata wetmorel) by Leopold (1963), both previously presumed extinct (Bond, 1956, 1961), indicated that the inventory of the Puerto Rican avifauna might be incomplete. The largest remaining forest in Puerto Rico is in the Sierra de Luquillo at the island's eastern end. In September 1968 the senior author and his wife established residence within the forest at an elevation of 770 m, and began intensive studies of the Puerto Rican Parrot (Amazona vittata) and the Puerto Rican Tody (Todus mexicanus). These studies included a series of census routes through the forest to assess easonal and altitudinal distribution a d abundance of these and other species (Kepler and Kepler, 1970). Two census routes were established in Elfin Woodland (Figure 1), a distinctive forest type confined to the higher peaks and ridges. In this forest they occasionally noticed a warbler of peculiar appearance, but were unsure of its identity because of the difficulty of seeing small birds in this habitat. The bird (see Frontispiece) showed similarities both to the Blackand-white Warbler (Mniotilta varia), a common North American migrant to Puerto Rico, and the Arrow-headed Warbler (Den•oica pharetra), a