Nearctic Migrants Research Articles

Avian assemblages associated with different grasslands managements in cattle production systems in the pampas of Argentina

Modifications in the structure of grasslands have been responsible for the decline of several avian species due to a reduced quality in available habitat. Currently, applications of the herbicide glyphosate have been introduced to promote winter forage production in the Flooding Pampas of Argentina. Rotational grazing has been another technique used to promote winter forage production. Here, we evaluated different grasslands managements in cattle production systems on species richness, composition, and abundance of bird assemblages in grasslands Pampas. We put emphasis on responses of two neartic migratory shorebirds, the Buff-breasted Sandpiper (Calidris subruficollis) and the American Golden Plover (Pluvialis dominica). The three treatments on natural grassland were: (1) paddocks of Ryegrass growth promotion through the application of herbicide glyphosate; (2) paddocks managed with Rotational grazing, and 3) paddocks managed with Continuous grazing. We considered three periods of the breeding cycle of the birds (early, late, post-breeding) for two years (2011/2012, 2012/2013). Vegetation cover lower than 10 cm was greater in both Rotational and Continuous grazing sites in comparison to the ryegrass promotion sites. A NMDS analysis revealed a clear separation in structure of bird communities among the three grazing treatments. The abundance of total birds and of short grassland birds was lower in grasslands with Ryegrass promotion. An indicator species analysis revealed the associations of shorebirds with Rotational and Continuous grazing sites. Grassland management with glyphosate application had an effect on the structure of assemblages of grassland birds in the Flooding Pampas, which was negative particularly with Nearctic migrants of conservation importance.

Notocotylus chionis (Trematoda: Notocotylidae) and Notocotylus sp. from shorebirds in southern Patagonian wetlands of Argentina: morphological and molecular studies

Southernmost South America provides significant wintering habitats for migrant shorebirds, most of which breed in the High Arctic tundra. Helminth species parasitizing these migratory birds have been well studied in North America; however, in South America they are poorly known. As part of an ongoing research on the helminth fauna from Patagonian birds in Argentina, we report Notocotylus chionis and Notocotylus sp. (Trematoda: Notocotylidae) parasitizing three shorebird species, the Nearctic migrants Calidris fuscicollis (WRSA) and Calidris bairdii (BASA) (Scolopacidae), and the Neotropical Charadrius falklandicus (TBPL) (Charadriidae). We provide a new morphological description of N. chionis considering that the previous one reported from the snowy sheathbill on Subantarctic islands are incomplete and based on few specimens. We also provided a morphometric characterization of Notocotylus sp. We obtained molecular data which confirmed the identification of specimens recovered from WRSA and TBPL as N. chionis. Phylogenetic analysis based on 28S ribosomal DNA sequences was performed. The results placed N. chionis close to other Patagonian species native to South America (i.e. N. primulus). Notocotylus chionis was found previously in the snowy sheathbill which inhabits in coasts of southern South America, Antarctic Peninsula and surrounding islands. Present finding in resident birds (TBPL) allows us to hypothesize that N. chionis is a Neotropical species whose life cycle is being completed in southern South America and Subantarctic islands and represents a valuable contribution to the knowledge of parasite diversity in the austral subpolar region of the western hemisphere.

The Tocantins-Araguaia Basin as a migratory route and a wintering area of Falco peregrinus (Aves, Falconidae)

The Peregrine Falco peregrinus, is an Nearctic migrant to Brazil where its status in central Brazil is still poorly known. Herein we present a compilation of records of the species from the state of Tocantins and comment on its use of a wintering site in the state of Goiás. These records show that the Tocantins-Araguaia River Basin is a migration route for the species, and therefore a mid-continental migration route through the interior of South America.

Length polymorphisms at two candidate genes explain variation of migratory behaviors in blackpoll warblers (Setophaga striata).

Migratory behaviors such as the timing and duration of migration are genetically inherited and can be under strong natural selection, yet we still know very little about the specific genes or molecular pathways that control these behaviors. Studies in candidate genes Clock and Adcyap1 have revealed that both of these loci can be significantly correlated with migratory behaviors in birds, though observed relationships appear to vary across species. We investigated geographic genetic structure of Clock and Adcyap1 in four populations of blackpoll warblers (Setophaga striata), a Neotropical–Nearctic migrant that exhibits geographic variation in migratory timing and duration across its boreal breeding distribution. Further, we used data on migratory timing and duration, obtained from light‐level geolocator trackers to investigate candidate genotype–phenotype relationships at the individual level. While we found no geographic structure in either candidate gene, we did find evidence that candidate gene lengths are correlated with five of the six migratory traits. Maximum Clock allele length was significantly and negatively associated with spring arrival date. Minimum Adcyap1 allele length was significantly and negatively associated with spring departure date and positively associated with fall arrival date at the wintering grounds. Additionally, we found a significant interaction between Clock and Adcyap1 allele lengths on both spring and fall migratory duration. Adcyap1 heterozygotes also had significantly shorter migration duration in both spring and fall compared to homozygotes. Our results support the growing body of evidence that Clock and Adcyap1 allele lengths are correlated with migratory behaviors in birds.

Seasonal variation in migration strategies used to cross ecological barriers in a nearctic migrant wintering in Africa

Ecological barriers such as oceans, mountain ranges or glaciers can have a substantial influence on the evolution of animal migration. Along the migration flyway connecting breeding sites in the North American Arctic and wintering grounds in Europe or Africa, nearctic species are confronted with significant barriers such as the Atlantic Ocean and the Greenland icecap. Using geolocation devices, we identified wintering areas used by ringed plovers nesting in the Canadian High‐Arctic and investigated migration strategies used by these nearctic migrants along the transatlantic route. The main wintering area of the ringed plovers (n = 20) was located in western Africa. We found contrasting seasonal migration patterns, with ringed plovers minimizing continuous flight distances over the ocean in spring by making a detour to stop in Iceland. In autumn, however, most individuals crossed the ocean in one direct flight from southern Greenland to western Europe, as far as southern Spain. This likely resulted from prevailing anti‐clockwise winds associated with the Icelandic low‐pressure system. Moreover, the plovers we tracked largely circumvented the Greenland icecap in autumn, but in spring, some plovers apparently crossed the icecap above the 65°N. Our study highlighted the importance of Iceland as a stepping‐stone during the spring migration and showed that small nearctic migrants can perform non‐stop transatlantic flights from Greenland to southern Europe.

Nasal mites (Mesostigmata, Rhinonyssidae) in Sternidae (Aves: Charadriiformes) on the southern Coast of Brazil.

Six species of birds of the family Sternidae are often found on the southern coast of South America. Sterna trudeaui, S. hirundinacea, Thalasseus maximus, T. acuflavidus and Sternula superciliaris are South American residents and Sterna hirundo, a Nearctic migrant. At least 500 species of nasal mites have been described around the world, and Rhinonyssidae is the most diverse family. These mites are bloodsucking endoparasites that inhabit the respiratory system of birds. This study aimed to report on occurrences of nasal mites in Sternidae on the southern coast of Brazil. Of the 106 birds analyzed, 8.5% (9 birds) were parasitized by nasal mites. This report provides the first record in the Neotropical region for two mite species, Sternostoma boydi and Larinyssus orbicularis parasitizing Thalasseus acuflavidus and Sternula superciliaris. No nasal mites were found in Sterna trudeaui or Thalasseus maximus. One host individual (T. acuflavidus) was parasitized by two species of nasal mites, S. boydi and L. orbicularis.

Shorebird Population Estimates Using Seasonal Aerial and Terrestrial Surveys at Samborombón Bay, Argentina

Abstract. Information about shorebirds is essential for predicting the impact of natural and human-mediated changes on their populations. Aerial and terrestrial surveys were performed to characterize shorebird abundance, spatial distribution and assemblage composition at Samborombon Bay, Argentina, during different tide levels and seasons. Approximately 60,000 shorebirds were observed using the intertidal flats. Highest abundances occurred during austral summer, autumn and spring when Nearctic migrants dominate the assemblage. Significant percentages (> 1%) of the populations of three Nearctic migrants [American Golden-Plover (Pluvialis dominica), Hudsonian Godwit (Limosa haemastica), and White-rumped Sandpiper (Calidris fuscicollis)], one Neotropical migrant [Two-banded Plover (Charadrius falklandicus)], and two resident species [American Oystercatcher (Haematopus palliatus) and Black-necked Stilt (Himantopus mexicanus)] were estimated. Large numbers of Semipalmated Plovers (C. semipalmatus), Rufous-ches...

Subarctic‐breeding passerines exhibit phenological resilience to extreme spring conditions

AbstractThere has been relatively little study of the capacity of subarctic passerines to adjust their phenologies to rapid changes on their breeding grounds. Here, we assess variation in passerine arrival timing in Denali National Park, Alaska, from 1995 to 2015, a period that included both the warmest and coldest recorded mean spring temperatures for the park. Using an open‐population occupancy modeling approach in which arrival events are random variables, we investigated interannual variation in the arrival distribution for 10 Nearctic–Nearctic migrants, three Nearctic–Neotropical migrants, and one Palearctic migrant. Neotropical–Nearctic migrants varied in terms of the flexibility of their arrival timing, but generally showed plastic phenologies, suggesting resilience under extreme spring conditions. In comparison, Nearctic–Nearctic migrants showed similar or greater plasticity in arrival timing. A majority of species showed synchronous–asynchronous fluctuation in arrival (i.e., synchronous arrival in some years, asynchronous in others) in combination with various levels of the mean response (i.e., early, average, and late arrival), suggesting the presence of interactions between environmental conditions at multiple scales and inter‐individual variation. The presence of synchronous–asynchronous fluctuation in arrival suggests that weakening of the north–south temperature gradient under continued Arctic amplification may strongly affect arrival variances. Our results also suggest that complex interactions between distributional and phenological changes may be possible. For example, the arrival distribution of Fox Sparrow (Passerella iliaca) became more synchronized over time, a pattern that coincided with a dramatic increase in occupancy probability through expansion of its elevational distribution. Overall, our findings suggest that monitoring of the mean–variance relationship may lead to a deeper understanding of the factors shaping phenological responses.

Birds of a wildlife reserve in the South American Pampa (Córdoba, Argentina)

In the Pampa ecoregion of South America, the intensification of agriculture has led to the almost total replacement of pristine vegetation by agroecosystems. This has caused a great loss of biodiversity and a decline of bird assemblages. We monitored birds in Dos Hermanas Wildlife Reserve, an integrated ecosystem-based management area in preserved natural saline wetland relicts (grasslands and shrublands) with a cultivated sector (sustainable grazing and organic crops). We recorded a total of 170 species, including altitudinal migrants, Nearctic migrants, migrants of the temperate-tropical and cold-temperate systems, and residents. Seven are globally threatened species and three are exotic species. The high diversity of birds recorded at Dos Hermanas Wildlife Reserve highlights the importance of this reserve for the conservation of the regional biota. The application of ecosystem-based management allows the presence of contrasting vegetation structures with positive effects on the diversity of bird assemblages in the Pampa region.

Change in Numbers of Resident and Migratory Shorebirds at the Cabo Rojo Salt Flats, Puerto Rico, USA (1985–2014)

Abstract. North American migratory shorebirds have declined markedly since the 1980s, underscoring the importance of population surveys to conduct status and trend assessments. Shorebird surveys were conducted during three multi-year periods between 1985 and 2014 and used to assess changes in numbers and species composition at the Cabo Rojo Salt Flats, Puerto Rico, USA, a site of regional importance in the eastern Caribbean. Eight fewer species (total = 21) were recorded in 2013–2014 as compared to the 29 from 1985–1992; all eight species were Nearctic migrants. Small calidrids had the highest population counts; however, this suite of species and all others experienced a ≥ 70% decline. Combined counts from the salt flats and neighboring wetlands in 2013–2014 were lower than counts only from the Cabo Rojo Salt Flats in two previous multi-year survey periods, which indicated a real change in numbers not just a shift in wetland use. Invertebrate prey density was lower in 2013–2014 than in 1994. Body fat cond...

Shorebird Seasonal Abundance and Habitat-Use Patterns in Punta Rasa, Samborombón Bay, Argentina

Shorebird assemblage composition and habitat-use patterns were characterized at Punta Rasa during the austral summer, autumn and winter. Compared to other sites within the region, this area showed high species richness, reflected by a total of 22 species recorded within a relatively short time frame. Differences in assemblage structure were driven by the use of estuarine mudflats and oceanic sandy beaches as feeding habitats. During low tide, more species used estuarine environments, achieving the highest total densities. Abundance patterns and assemblage composition also changed seasonally. Maximum total abundance occurred during the austral summer, and minimum total abundance during the austral winter. During the austral summer, the assemblage was dominated by Nearctic migrants such as American Golden-Plover (Pluvialis dominica), Hudsonian Godwit (Limosa haemastica) and White-rumped Sandpiper (Calidris fuscicollis). In addition, Two-banded Plover (Charadrius falklandicus) and American Oystercatcher (Haematopus palliatus) were abundant during the austral autumn. The Red Knot (Calidris canutus), a shorebird that dominated the austral autumn assemblage 25 years ago, was recorded in relatively small numbers during this study, probably reflecting the global population trend of a subspecies of the Red Knot (C. c. rufa) in the past two decades. During the austral winter, resident birds largely dominated the assemblage. However, it is noteworthy that some individuals of nine Nearctic migrant species remained in the area. In the case of the endangered Red Knot, Punta Rasa is, along with Lagoa do Peixe in Brazil, one of the sites in South America with the highest known abundances during the austral winter.

Do Nearctic migrant birds compete with residents at army ant raids? A geographic and seasonal analysis

ABSTRACT Army ant swarm raids in Neotropical montane forest are attended by diverse flocks of foraging birds that can include residents year-round and overwintering Nearctic migrants. We asked whether migrants and residents affect each other's ability to forage at army ant raids. We quantified variation in raid attendance by three guilds of birds: wintering migrants, regular and obligate raid attending residents (ant-following residents), and facultative raid attending residents. To test whether wintering migrants and residents were negatively associated at raids, we collected data on raid attendance in four adjacent life zones in the Tilaran Mountains of Costa Rica and in different seasons (when migrants were present and absent). We first compared the guilds' raid attendance among life zones. There was little geographic overlap of migrants and ant-following residents at raids, and raid attendance frequencies were strongly correlated with the estimated local abundances of these bird guilds in each life zo...

Density, habitat use, and opportunities for conservation of shorebirds in rice fields in southeastern South America

Worldwide, shorebirds are a major component of rice field avian biodiversity. Rice fields in Argentina and southern Brazil hold large numbers of shorebirds and have been recognized as important areas for migrating or wintering species. To develop successful shorebird conservation strategies, we need to understand geographic variation in shorebird abundance in rice fields as well as how bird use of rice fields varies over the rice growing cycle. We surveyed shorebirds in November and December in the main rice cultivation regions of interior Argentina and coastal Brazil to estimate shorebird densities using distance sampling and to evaluate densities of individual species at different stages of the rice cycle. We detected >7,000 shorebirds in rice fields, including a variety of Nearctic migrants. Density of resident species was generally low and showed no differences between countries. Densities of migratory taxa were higher and varied between Brazil and Argentina. Pectoral Sandpiper (Calidris melanotos) and Lesser Yellowlegs (Tringa flavipes) were the most common species in Argentina, but White-rumped Sandpiper (Calidris fuscicollis) and American Golden-Plover (Pluvialis dominica) were the most common species in Brazil. Pectoral Sandpiper density was nearly 8 times higher in Argentina than in Brazil; densities of the White-rumped Sandpiper and American Golden-Plover were 33 and 25 times higher in Brazil than in Argentina. Shorebird density was highest in lightly flooded paddies with rice height <20 cm. Our findings confirm the importance of rice paddies for shorebirds in southeastern South America and emphasize the need for detailed assessments to ensure that agricultural chemical and water management practices are biodiversity friendly.

Seasonal Variation in the Foraging Behavior of Some Migratory Western Wood Warblers

-I observed the foraging behavior of four warbler species (Dendroica petechia, Oporornis tolmiei, Geothlypis trichas, and Wilsonia pusilla) in the summer in Wyoming and in the winter in Nayarit, Mexico. Of six variables (absolute foraging height, relative foraging height, vegetation density, horizontal foraging position, feeding method, and foraging substrate) believed to be potentially important in distinguishing the warbler species ecologically, the two foragingheight variables provided the greatest separation of the four species in both summer and winter. An analysis of the behavioral similarity of each species from summer to winter revealed that feeding method was the least changed behavior and that absolute foraging height involved the greatest behavioral flexibility. The behaviors that are most flexible are possibly the least well tied to the birds' morphology and are also the ones that have been shown by other workers to reveal the effects of competitors through shifts. Therefore, ecological relationships among coexisting species (in terms of overlaps or positions in niche space) may never be fully derivable from morphological information alone. Received 6 March 1980, accepted 24 March 1981. ECOLOGICAL studies of Nearctic migrants on their breeding grounds are relatively common, but such studies on their wintering grounds are less common (but see Eaton 1953, Schwartz 1964, Willis 1966, Lack and Lack 1972, Leck 1972, Tramer 1974, Rappole 1975, Chipley 1976, Karr 1976, Mills 1976, Post 1978, Wilz and Giampa 1978, or some of the more recent studies included in Keast and Morton 1980). Comparative studies that deal with the ecology of migratory species on both their breeding and wintering grounds are rarer still (but see Root 1967, Baker and Baker 1973, Lack 1976, Bennett 1980, Rabenold 1980). Only through such comparative studies will we begin to understand the extent to which the morphology of a species represents a compromise among behaviors that vary seasonally (Fretwell 1972). In this paper I quantify the foraging behavior of four species of migratory wood warblers (Yellow Warbler, Dendroica petechia; MacGillivray's Warbler, Oporornis tolmiei; Common Yellowthroat, Geothlypis trichas; and Wilson's Warbler, Wilsonia pusilla) that can be found syntopically during both the breeding and nonbreeding seasons in western North America to determine (1) whether several potential mechanisms of ecological isolation change seasonally, and (2) which aspect of foraging behavior shows the grestest seasonal flexibility. STUDY SITES AND METHODS I collected foraging data on the four warbler species from 20 May-20 June 1975 within 4 ha of willow (Salix) habitat adjacent to the Jackson Hole Biological Research Station, Grand Teton National Park Wyoming (43?52'N, 1 10'34'W). Willows were the only large plants growing in the study area, and the open areas between them were filled with grasses and sedges. A foliage-height profile, which depicts the porportion of vegetation at different heights, is given in Fig. 1. Winter foraging data were collected from 15 January to 15 February 1975 and 1976 in second growth Present address: Department of Zoology, University of Montana, Missoula, Montana 59812. 765 The Auk 98: 765-777. October 1981 This content downloaded from 150.131.112.212 on Wed, 16 Oct 2013 20:33:09 PM All use subject to JSTOR Terms and Conditions 766 RICHARD L. HUTTO [Auk, Vol. 98

Feather growth rate and mass in Nearctic passerines with variable migratory behavior and molt pattern

ABSTRACT. Bird species vary greatly in the duration of their annual complete feather molt. However, such variation is not well documented in birds from many biogeographic areas, which restricts our understanding of the diversification of molt strategies. Recent research has revealed that molt duration can be estimated in passerines from ptilochronology-based measurements of the growth rate of their tail feathers. We used this approach to explore how molt duration varied in 98 Nearctic species that have different migratory strategies and molt patterns. As previously documented for Palearctic species, migration was associated with a shortening of molt duration among species that molted during summer on their breeding range. However, molts of winter-molting migratory species were as long as those of summer-molting sedentary species, which suggests that winter molt also allows Nearctic migrants to avoid the temporal constraints experienced during summer. Our results also suggest that migratory species that un...

Migratory flows and foraging habitat selection by shorebirds along the northeastern coast of Brazil: The case of Baía de Todos os Santos

Large numbers of Nearctic shorebirds migrate and winter along the coast of northeastern Brazil, but there is little information on their migratory flows, foraging ecology, and on the structure of the species assemblages that they form with resident shorebirds. We studied these issues on intertidal flats of Baía de Todos os Santos (Bahia), the second largest bay in Brazil. During a full year cycle we carried out weekly bird counts in an intertidal area of 280 ha divided in sectors, where we also measured environmental parameters. The analyses of weekly counts resulted in a detailed phenology of use of the area by shorebirds. Five species were resident and ten were Nearctic migrants. Several of the latter had clear peaks in numbers in March and October, revealing the use of the bay as a stopover during both the north-bound and south-bound migration flows. A canonical correspondence analysis of the relationship between environmental parameters and bird numbers indicated that the foraging bird assemblage could be divided into five main groups, occupying distinct ecological gradients in the study area. The most important factors driving this structure were invertebrate prey abundance, percentage of fine sediments, area of mangrove cover and distance to channels. Our findings imply that maintenance of the diversity of intertidal habitats in this bay is crucial to satisfy the particular habitat requirements of resident and migrant shorebirds using the northeastern coastal regions of Brazil.

Evolutionary history of a prominent North American warbler clade: The Oporornis–Geothlypis complex

The avian genera Oporornis and Geothlypis are thought to represent a single lineage of closely related New World wood-warbler (AOU Family Parulidae) species. Phylogenetic relationships within this assemblage have not yet been addressed using molecular genetic methods. We used sequence data from three mitochondrial (mtDNA) genes (cytochrome b, ND2, and control region) to reconstruct an hypothesis of relationships for this group. Our ingroup sampling included 34 individuals representing all currently recognized Oporornis (4 spp.) and Geothlypis (9 spp.) species. Our results indicate that Geothlypis is paraphyletic with respect to Oporornis formosus. The four members of Oporornis do not form a clade but instead comprise a grade at the base of the Oporornis–Geothlypis topology. Two species within Geothlypis are polyphyletic. The Costa Rican form of G. a equinoctialis is embedded within the Neotropical G. semiflava complex, and the widespread North American form G. trichas consists of at least two groups, each having a closer affinity to other Geothlypis species than with each other. Five Geothlypis species differ from one another on average by about 2% uncorrected (cytochrome b) divergence, indicating a rapid and recent radiation within this genus. Our phylogenetic hypothesis for this assemblage indicates that morphological characters such as size and plumage brightness that have traditionally defined relationships with Geothlypis are not concordant with molecular data. Most members of Geothlypis are sedentary whereas all members of Oporornis are long-distance Nearctic migrants. Our topology suggests that Geothlypis is derived from a migrant, Oporornis-like ancestor that ceased migration and established itself as a sedentary breeding population in the Neotropics. We speculate that an ecological switch from forested to more open habitats at this time led to range expansion and diversification in this new lineage.

Variation in Plumage Microbiota Depends on Season and Migration

Migratory birds can be efficient dispersers of pathogens, yet we know little about the effect of migration and season on the microbial community in avian plumage. This is the first study to describe and compare the microbial plumage community of adult and juvenile migratory birds during the annual cycle and compare the plumage community of migrants to that of resident birds at both neotropical and nearctic locations. We used length heterogeneity PCR (16S rRNA) to describe the microbial assemblage sampled from the plumage of 66 birds in two age classes and from 16 soil samples. Resident birds differed significantly in plumage microbial community composition from migrants (R > or = 0.238, P < 0.01). Nearctic resident birds had higher plumage microbial diversity than nearctic migrants (R = 0.402, P < 0.01). Plumage microbial composition differed significantly between fall premigratory and either breeding (R > or = 0.161, P < 0.05) or nonbreeding stages (R = 0.267, P < 0.01). Six bacterial operational taxonomic units contributed most to the dissimilarities found in this assay. Soil microbial community composition was significantly different from all samples of plumage microbial communities (R > or = 0.700, P < 0.01). The plumage microbial community varies in relation to migration strategy and stage of the annual cycle. We suggest that plumage microbial acquisition begins in the first year at natal breeding locations and reaches equilibrium at the neotropical wintering sites. These data lead us to conclude that migration and season play an important role in the dynamics of the microbial community in avian plumage and may reflect patterns of pathogen dispersal by birds.

The birds at Ilha Comprida beach (São Paulo State, Brazil): a multivariate approach

Birds were censused weekly from January 1999 to January 2001 along Ilha Comprida beach, a barrier island off São Paulo, southeastern Brazil. To evaluate the similarity in the bird's species composition among the weekly surveys, species counts data were arranged on a data matrix with 144 weekly surveys, analyzed following a multivariate analysis protocol. We counted a total of 205,399 individuals and 52 species. Migratory birds were an important component of the avifauna (maximum N = 21,294 individuals and 14 species). The largest numbers of birds were observed during summer, when Nearctic migrants arrive. All 14 of the most common species were migrants, including Calidris alba, Sterna maxima, Charadrius semipalmatus, Sterna hirundo, Thalasseus maximus, Pluvialis dominica and Calidris fuscicollis. The most common residents were Thalasseus s. eurrygnathus, Larus dominicanus, Coragyps atratus, Fregata magnificens and Sterna hirundinacea. Recently, most of the peripheral area adjacent to the beach has been urbanized and rapid habitat change is progressing. In this paper, we establish a reference that will allow future comparisons to assess the impact of such urbanization on the composition of bird populations on Ilha Comprida.

Aves marinas de la Isla del Coco, Costa Rica, y su conservación

Seabirds of Cocos Island, Costa Rica, and their conservation. The marine avifauna of Cocos Island includes 32 species, 17 genera and nine families. Eight of these species are reproductive residents and 25 are visitors. Among visitors, eight are Nearctic migrants, 11 are tropical species and 13 correspond to the Eastern Pacific geographic range. According to presence/abundance observations, six species are abundant (18.75%), one, common (3.13%), three, uncommon (9.37%), ten, casual (31.25%) and twelve, accidental (37.50%). I recommend a study of human impact, the establishment of an official checklist and periodical monitoring of this avifauna, and a better spatial definition of the coastal marine belt. Rev. Biol. Trop. 56 (Suppl. 2): 133-149. Epub 2008 August 29.