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Predator-prey relationship between Wilson's plovers and fiddler crabs in northeastern Venezuela
... Shorebirds are ideal subjects for studies of selective foraging, and many attempts have been made to relate their prey preferences to prey availability (e.g. Rands & Barkham 1981;Piersma et al. 1993;Kalejtja & Hockey 1994;McNeil et al. 1995;Thibault & McNeil 1995). Several studies have shown that prey availability depends not only on the total number of prey present, but also on behavioural interactions between predator and prey (Zwarts 1985;Kersten et al. 1991;Ens et al. 1993). ...
... These interactions are particularly important when prey animals, such as fiddler crabs (Uca spp.), are able to detect and evade potential predators. The availability of fiddler crabs to shorebirds has usually been estimated by counting either the number of open burrows in an area, or the number of crabs active on the surface when a predator is not present (Zwarts 1985(Zwarts , 1990Ens et al. 1993;Thibault & McNeil 1995). These simple measures of prey availability have been intuitively accepted despite mounting evidence of their inaccuracy (Goss-Custard 1984;Zwarts 1985Zwarts , 1990Ens et al. 1993;Kalejta 1993;Thibault & McNeil 1995). ...
... The availability of fiddler crabs to shorebirds has usually been estimated by counting either the number of open burrows in an area, or the number of crabs active on the surface when a predator is not present (Zwarts 1985(Zwarts , 1990Ens et al. 1993;Thibault & McNeil 1995). These simple measures of prey availability have been intuitively accepted despite mounting evidence of their inaccuracy (Goss-Custard 1984;Zwarts 1985Zwarts , 1990Ens et al. 1993;Kalejta 1993;Thibault & McNeil 1995). If earlier studies incorrectly estimated the relative abundance of different size and sex classes, this may have led to incorrect assessments of foraging selectivity by shorebirds and sexbiased predation on fiddler crabs (see Boshe 1982;Zwarts 1985Zwarts , 1990Ens et al. 1993). ...
Accurate measurements of prey availability are vital to our understanding of foraging behaviour, particularly prey selectivity. In the present study, observations of shorebirds foraging for fiddler crabs on intertidal mudflats demonstrate that prey availability depends both on the temporal variation in crab activity and on the crabs’ responses to the presence of foraging shorebirds. Our results suggest that measurements of prey availability that do not specifically account for prey activity patterns and their responses to predators are neccessarily inaccurate. Furthermore, our results also show that tests for foraging selectivity are extremely sensitive to the way in which prey availability is measured and can even indicate active prey selectivity when more accurate measures of prey availability show predators to be non-selective. Because inaccurate measures of food resources greatly reduce our ability to detect food preferences, greater care must be taken to account for prey activity patterns and their responses to predators in measurements of prey availability.
... Aportes al conocimiento de la ecología y biología reproductiva de esta subespecie en el Caribe colombiano fueron realizados por Pantaleón & Rodríguez (2001) en el Santuario de Fauna y Flora Los Flamencos, y por Naranjo (1979) y Reyes-Herrera & Ruiz-Guerra (2001) en el Vía Parque Isla de Salamanca. En Venezuela, Morrier & McNeil (1991) evaluaron el tiempo invertido en la actividad de movimiento y en la incubación por parte de machos y hembras de día y de noche, y Thibault & McNeil (1994,1995 sugirieron que la búsqueda nocturna de alimentos en periodo no reproductivo por parte de la especie es una estrategia para evitar depredadores diurnos como las rapaces. ...
Estudiamos algunos aspectos de la reproducción de dos subespecies del Chorlito Piquigrueso (Charadrius wilsonia beldingi y C. w. cinnamominus) en dos sitios de anidación en Colombia, uno en el Parque Nacional Natural Sanquianga, localizado en la costa del Pacífico y el otro en la Vía Parque Isla de Salamanca, en la costa Caribe. La reproducción de estas dos subespecies ocurre entre los meses de marzo y agosto, con una postura de aproximadamente tres huevos que eclosionan en 21-22 días. En Salamanca, encontramos cuatro nidos de la subespecie cinnamominus, mientras que en Sanquianga encontramos 35 nidos de la subespecie beldingi, localizados en playas arenosas con escasa vegetación cercanas a manglar. Los nidos encontrados en Salamanca estuvieron cerca de vegetación baja y presentaron material en el fondo, contrario a los nidos de Sanquianga que frecuentemente se ubicaron cerca de objetos arrojados por el mar y sólo presentaron material circundante. Este estudio resalta el valor del PNN Sanquianga como sitio de importancia para la reproducción del Chorlito Piquigrueso en Colombia.
... While not well studied, the diet of Piping Plovers and Snowy Plovers is similar and varies by location and season, but polychaete worms and other invertebrates appear to be common items [5,10,11,22]. Also poorly studied, Wilson's Plovers also eat invertebrates but prefer larger species, particularly fiddler crabs (Uca spp.) [6,23,24]. ...
Simple Summary
This research studied three species of imperiled shorebirds—Piping Plover, Snowy Plover, and Wilson’s Plover—that are similar in appearance and share habitats outside the breeding season. Researchers counted the number of these birds on a barrier island in Southwest Florida and examined how tide and wind affected their abundance and foraging behavior. They found that all three species were more likely to be found on the mudflats during lower tides and on the beach during higher tides. All of the feeding observed was on the mudflat, but one of the species, Wilson’s Plovers, was never observed feeding during the study. The high densities of these plover species are likely due to the mudflat habitat that provides more food, a beach habitat that provides a relatively safe location to roost, and the location of the barrier island, which is surrounded by other good places to forage and rest. While each species used the barrier island’s habitats slightly differently, the high densities of all three species present an opportunity to have a large conservation impact by protecting this dynamic area.
Abstract
Piping Plover (Charadrius melodus), Snowy Plover (Charadrius nivosus), and Wilson’s Plover (Charadrius wilsonia) are imperiled species that overlap in both their range and habitat outside the breeding season. The purpose of this research was to document the abundance of these species at a barrier island in Southwest Florida, USA, and to examine the influence of tide and wind on both their abundance and foraging. We walked ~700 m surveys through tidal mudflat and adjacent beach semiweekly at 0730–1030 from 24 September 2021–4 March 2022. During these 38 surveys, Piping Plovers were the most abundant of the three species, and the average number counted was 34 (SD 17.3) compared with 11 (SD 6.3) Snowy Plovers and 14 (SD 14.1) Wilson’s Plovers. All of the species were more likely to be found on the mudflats during low tides and the beach during high tides. Our findings suggest the high densities of Piping, Snowy, and Wilson’s Plover are due to a mudflat habitat that provides high availability of prey, a beach habitat that provides a relatively safe location to roost, and the context of the barrier island, which is surrounded by other suitable habitats. While each species used the barrier island’s habitats slightly differently, the high densities of all three species present an opportunity to have a large conservation impact by protecting this dynamic area.
... They visually recognize predators (Hemmi 2005b) and also utilize social information from conspecifics escaping to burrows, to escape to their own burrows (Wong et al. 2005;Muramatsu 2021). The predator of fiddler crabs is known to be birds (Thibault and McNeil 1995;Backwell et al. 1998;Koga et al. 1998Koga et al. , 2001Iribarne and Martinez 1999) and crabs (Pratt et al. 2002;Kuroda et al. 2005;Moto and Wada 2016). ...
The flight initiation distance model predicts that prey initiates to escape at a point where the cost of staying exceeds its benefits that they acquire from staying, such as the availability of food resources and mates. Social behaviors, such as courtship or territorial behaviors can generally increase reproductive success, although they have the potential to attract predators. Using refuge enhances the probability of survival. Therefore, for prey, social behaviors increase the benefits, and the use of refuge decreases the costs of staying. However, most empirical studies testing these predictions have used human approaches as predator mimics and have not represented natural predation events in the field. We quantified predator–prey interactions between the predator, the varunid crab (Helicanajaponica), and its prey, the fiddler crab (Austruca lactea), based on field observations. We then demonstrated the effects of social behaviors and distance from a refuge on predation risk and the adjustment of distance according to the predator–prey distance. Fiddler crabs adjusted the prey-prey burrow distances according to the predator–prey distance when it was < 45 cm. When > 45 cm, the prey-prey burrow distances did not influence it. The varunid crabs were shown to target prey that were closer in distance. Predators physically reached prey that were further from their burrows. These results show that predation risk caused prey to regulate prey-prey burrow distances according to predator–prey distances. In addition, varunid crabs frequently contacted fiddler crabs that employed social behaviors, suggesting that social behaviors elevated predation risk.
Significance statement
We quantified predator-prey interactions between the predatory varunid crab and the prey fiddler crab from field observations. We demonstrated that fiddler crabs adjusted their distance from their burrows according to the predator-prey distances. Varunid crabs targeted prey that were closer. Prey that were reached by the predator were situated further away from their burrows and frequently employed social behaviors. These results suggest that the social behaviors of prey elevate predation risk, although prey adjust the distance from the burrow according to the predator-prey distance.
... Fiddler crabs also serve as a primary food source for a wide range of vertebrate and invertebrate taxa (Raut, 1943;Kushan, 1979;Subramanian, 1984;Petit & Bildstein, 1987;Zwarts & Dirksen, 1989, 1990Zwarts, 1990;Zwarts & Blomert, 1990;Grant, 1992;Turpie & Hockey, 1993;Lee & Kneib, 1994;McNeil & Rompré, 1995;Thibault & McNeil, 1995;De Santo et al., 1997;Backwell et al., 1998;Olmos et al., 2001;Vannini et al., 2001;Whitelaw & Zajac, 2002;Jennions et al., 2003;Hugie, 2004;Martínez, 2004;Ribeiro et al., 2004;Rulison, 2010;Rush et al., 2010;Lourenço et al., 2017;Alleman & Guillen, 2017), and are often viewed as a critical respondent to near-coast pollution events (Krebs & Burns, 1977;Burns & Teal, 1979;Lee et al., 1981;Deecaraman & Fingerman, 1985;Shafer & Hackney, 1987;Snowden & Ekweozor, 1987, Jacob, 1988Snowden & Ekweozor, 1990;Burger et al., 1991Teal et al., 1992;Culbertson, 2008;Chase et al., 2013;Zengel et al., 2016;Deis et al., 2017;Damare et al., 2018;Franco et al., 2018). ...
Fiddler crabs (Ocypodidae Rafinesque, 1815) occupy most tropical and semitropical coastlines worldwide where they are keystone species and ecosystem engineers. I present updated ranges for all 105 species and explore both global and local patterns to establish a baseline distribution as species ranges begin to shift with climate change. Globally, the average number of species per occupied coastline is five, with only limited allopatry observed within the group. Cohesive species assemblages were used to define four zoogeographic fiddler realms containing 24 provinces and transitional zones. These regions can serve as units of study when trying to explore which factors influence the distribution of coastal species.
... Se alimenta durante el día y la noche usando el sentido de la vista, su modo de forrajeo incluye corridas rápidas y ataques directos a la presa que preferentemente son crustáceos, principalmente cangrejos violineros del género Uca spp. (Strauch y Abele 1979, Thibault y McNeil 1994, 1995. ...
Este documento técnico presenta la información completa de tres años de investigación sobre aves playeras en Ecuador. Este documento sirve como un respaldo al Resumen Ejecutivo del Plan de Conservación de Aves Playeras recientemente publicado (Diciembre 2017).
... A bee looking for nectar profits from the knowledge of a flower opening its bloom at a certain time of day . Cyanobacteria replicate at night to do so without damaging ultraviolet radiation while some prey animals forage at this time avoid predators (Pittendrigh 1993;Thibault & McNeil 1995). For prediction of those recurring environmental rhythms though a sense of time and a way to measure time are needed. ...
... At Mida, crabs are frequently taken by Whimbrel, Terek Sandpiper, Lesser and Greater Sandplovers, and Grey Plovers. Crabs are the main prey for eight species of plovers, sandpipers and curlews in West Africa (Zwarts 1985), and for the Wilson's Plover Charadrius wilsonia in South America (Thibault and McNeil 1995). ...
The Crab Plover, a little known endemic species of the north and west coasts of the Indian Ocean and the only member of the family Dromadidae, was studied at Mida Creek, one of its main overwintering areas. Roosting and feeding alternated in relation to the tidal cycle. Feeding occurred both by day and by night, but in different areas. Prey were pursued chiefly by visual detection; tactile probing was also used but with low success. The diet included all prey types present within a 25 cm layer of mud, but prey which often come to the surface (crabs and molluscs) dominated, while worms which remain within the mud were preyed upon less frequently. Juveniles took less than half the weight of food taken per min by the adults, due to a lower capture rate and smaller prey. The juveniles seemed to have Che same rate of prey detection as the adults, but to be less able at prey capture, especially for prey thai, hide in mud and are presumably more difficult to catch. The overall feeding behavior of the Crab Plover is very similar to that of the Charadrius and Pluvialis waders.
... Aportes al conocimiento de la ecología y biología reproductiva de esta subespecie en el Caribe colombiano fueron realizados por Pantaleón & Rodríguez (2001) en el Santuario de Fauna y Flora Los Flamencos, y por Naranjo (1979) y Herrera & RuizGuerra (2001) en el Vía Parque Isla de Salamanca. En Venezuela, Morrier & McNeil (1991) evaluaron el tiempo invertido en la actividad de movimiento y en la incubación por parte de machos y hembras de día y de noche, y Thibault & McNeil (1994,1995) sugirieron que la búsqueda nocturna de alimentos en periodo no reproductivo por parte de la especie es una estrategia para evitar depredadores diurnos como las rapaces. A pesar de la información descrita arriba, el conocimiento de las poblaciones de C. wilsonia que anidan en Colombia aún presenta vacíos, lo cual resulta preocupante si se tiene en cuenta que la pérdida de hábitats importantes para aves playeras ha sido particularmente dramática en los últimos 100 años (Bildstein et al. 1991, Page & Gill 1994). ...
Estudiamos algunos aspectos de la reproducción de dos subespecies del Chorlito Piquigrueso (Charadrius wilsonia beldingi y C. w. cinnamominus) en dos sitios de anidación en Colombia, uno en el Parque Nacional Natural Sanquianga, localizado en la costa del Pacífico y el otro en la Vía Parque Isla de Salamanca, en la costa Caribe. La reproducción de estas dos subespecies ocurre entre los meses de marzo y agosto, con una postura de aproximadamente tres huevos que eclosionan en 21-22 días. En Salamanca, encontramos cuatro nidos de la subespecie cinnamominus, mientras que en Sanquianga encontramos 35 nidos de la subespecie beldingi, localizados en playas arenosas con escasa vegetación cercanas a manglar. Los nidos encontrados en Salamanca estuvieron cerca de vegetación baja y presentaron material en el fondo, contrario a los nidos de Sanquianga que frecuentemente se ubicaron cerca de objetos arrojados por el mar y sólo presentaron material circundante. Este estudio resalta el valor del PNN Sanquianga como sitio de importancia para la reproducción del Chorlito Piquigrueso en Colombia. ABSTRACT We studied some aspects related to breeding of two subspecies of Wilson's Plover (Charadrius wilsonia beldingi and C. w. cinnamominus) at two nesting sites in Colombia, one in Sanquianga National Park on the Pacific Coast, and the other in Isla de Salamanca National Park, on the Caribbean Coast. Both subspecies breed from March through August, with an approximate clutch size of three eggs, and an incubation period of 21-22 days. We found four nests of C. w. cinnamominus in Salamanca and 35 nests of C. w. beldingi in Sanquianga. The nests found in Salamanca were located close to vegetation and included material only in their bottom, in contrast to nests found in Sanquianga, which were often located near objects brought by the sea in sandy beaches with scant vegetation, and only included material in their periphery. This study highlights the importance of Sanquianga National Park as a breeding site for Wilson's Plover in Colombia.
... During daylight, vision is often relied upon for search and pursuit, while during darkness, nonvisual sensory systems typically have increased importance. Nocturnal foraging can be favoured, owing to increased prey susceptibility and availability (McMahon and Evans 1992;Thibault and McNeil 1995;Reimchen 1998a) and reduced predation risk and competition (Culp et al. 1991). Theoretically, the search for and pursuit of prey during darkness require reliance on different sensory modes and produce different costs and benefits than during daylight. ...
Brown bears (Ursus arctos) have been reported to be primarily diurnal throughout their range in North America. Recent studies of black bears during salmon migration indicate high levels of nocturnal foraging with high capture efficiencies during darkness. We investigated the extent of nocturnal foraging by brown bears during a salmon spawning migration at Knight Inlet in coastal British Columbia, using night-vision goggles. Adult brown bears were observed foraging equally during daylight and darkness, while adult females with cubs, as well as subadults, were most prevalent during daylight and twilight but uncommon during darkness. We observed a marginal trend of increased capture efficiency with reduced light levels (day, 20%; night, 36%) that was probably due to the reduced evasive behaviour of the salmon. Capture rates averaged 3.9 fish/h and differed among photic regimes (daylight, 2.1 fish/h; twilight, 4.3 fish/h; darkness, 8.3 fish/h). These results indicate that brown bears are highly successful during nocturnal foraging and exploit this period during spawning migration to maximize their consumption rates of an ephemeral resource.
... H. diversicolor tends to be more active at night (Evans, 1987), which makes it more conspicuous. Differences in the day and night activity of prey have been shown to cause changes in the foraging activity of waders (Thibault and McNeil, 1995;Kuwae, 2007). ...
Many species of waders forage extensively at night, but there is very little information on
the relevance of this behaviour for the energy budget of waders wintering in estuarine wetlands. Quantitative data on diurnal and nocturnal intake rates can indicate the extent to
which birds need to forage at night to supplement their diurnal energetic intake, or rather
show a preference for nocturnal foraging.
We compared day and night foraging behaviour, diet, and energy consumption of several
wader species in the Tejo estuary, Portugal. There were significant differences between diurnal and nocturnal foraging behaviour. In general, birds moved less at night and scolopacid waders tended to use more tactile foraging methods. Although birds consumed the same type of prey in the two periods, the relative importance of each type changed. Overall, energy consumption was higher during the day except in grey plover, which achieved higher crude intake rates at night.
Our results support the assertion that night foraging is an important part of the energy balance of waders during late winter, but that in most species it is less profitable than diurnal foraging.
... Grackles preferentially attack male over female U. beebi at breeding burrows, perhaps because the claw of males makes them easier to spot (Koga et al. 2001). However, fiddler crabs of all sizes have avian predators that target them (Zwarts 1985; Bildstein et al. 1989; Bildstein 1993; Thibault & McNeil 1995; Koga et al. 1998 Koga et al. , 2001 ). A diversity of predators could render males of all size classes approximately equally vulnerable. ...
Individuals can express boldness in their readiness to resume courtship signaling following a perceived threat. The degree of boldness that is selectively favored depends on the magnitude of costs and benefits that may vary across time and space. We examined within- and between-individual variation in the boldness of courting male sand fiddler crabs, Uca pugilator, across an entire breeding season at a South Carolina (USA) salt marsh where courtship is restricted to supratidal embankments. Boldness was assessed by the time to re-emergence and the number of re-emergences of males who were purposely startled into their breeding burrows once every 3 min for a total of five times. The two measures of boldness were significantly positively correlated. Courting males are on average bolder when their density is high and when tidal conditions correspond to peaks in the number of females moving over the embankment surface. Time to re-emergence increases with successive startles although some males consistently re-emerge faster than others. Large males are not bolder than small males. When male density is high, nearest neighbors frequently re-emerge at the same time, suggesting that males cue on the responses of other nearby males, perhaps by assessing substrate vibration. This may reduce the chance of losing a potential mate to a local competitor.
... Consequently, it is believed that shorebirds that detect prey by touch, without having to see them, would be able to feed as fast during darkness as during daytime, whereas birds that detect prey primarily by sight would be disadvantaged at night, unless having specialized adaptations favoring nocturnal vision [McNeil et al., 1992]. The Uca fiddler crabs, the preferred prey of Wil-son's Plover and the territorial Willet, contrary to abovementioned invertebrates, although swarming by thousands on intertidal mudflats both in the day and at night, are more active during daytime [McNeil and Rompré, 1995;Thibault and McNeil, 1995]. On moonless nights, territorial Willets have impaired vision, abandon their feeding territory, and move to habitats where they feed tactilely with non-territorial individuals [McNeil and Rompré, 1995;Rompré and McNeil, 1996]. ...
Some shorebird species forage with the same feeding strategy at night and during daytime, e.g. visual pecking in the Wilson's Plover (Charadrius wilsonia) or tactile probing in the Short-billed Dowitcher (Limnodromus griseus). The American Woodcock (Scolopax minor) uses tactile probing, by day and by night, but sometimes pecks for insects during daytime. The Black-winged Stilt (Himantopus himantopus) is a visual pecker, both by day and by night, and sometimes forages tactilely on windy (agitated water surface) moonless nights. Territorial Willets (Catoptrophorus semipalmatus) are visual peckers during daylight and on moonlight conditions but switch to tactile feeding under lower light conditions. It could be postulated that some shorebird species would switch from visual feeding during daytime to tactile foraging at night because they have poor night vision compared to species that are always sight foragers irrespective of the time of the day. This issue was examined by comparing retinal structure and function in the above species. Electroretinograms (ERGs) were obtained at different light intensities from anesthetized birds, and the retinae were processed for histological observations. Based on ERGs, retinal sensitivity, and rod:cone ratios, both plovers and stilts are well adapted for nocturnal vision. Although they have low rod density compared to that of stilts and plovers, Willets and woodcocks have a scotopic retinal sensitivity similar to that of stilts and plovers but rank midway between plovers and dowitchers for the b-wave amplitude. Dowitchers have the lowest scotopic b-wave amplitude and retinal sensitivity and appear the least well adapted for night vision. Based on photopic ERGs and cone densities, although stilts, Willets and dowitchers appear as well adapted for daytime vision, plovers occupy the last rank of all species examined. Compared to the nighttime tactile feeders and those that switch from daytime visual pecking to tactile feeding at night, nighttime sight feeders have a superior rod function and, consequently, potentially superior nocturnal visual capabilities.
The continuation of long-term avifaunal surveys conducted on St. Croix, U.S. Virgin Islands, from August 2004 through July 2012 (8 yr) resulted in new information on 87 species, 67 of which are rare to uncommon. However, our emphasis is on site-specific documentation of 16 rare to common breeding waterbirds and 3 columbids. We also provide documentation for individuals of 10 waterbird and 1 falcon species marked in North or South America or the Caribbean that were re-sighted or recovered on St. Croix. Four individuals of two of these species (Whimbrel (Numenius phaeopus) and Ruddy Turnstone (Arenaria interpres)) migrated to St. Croix more than once. We fully document vagrant and rare transient avian species that have occurred on St. Croix fewer than 10 times and rare to uncommon species that otherwise are of historical interest. We include five species previously unknown on St. Croix: Curlew Sandpiper (Calidris ferruginea), Great Black-backed Gull (Larus marinus), Black-billed Cuckoo (Coccyzus erythropthalmus), Greater Ani (Crotophaga major), and Fork-tailed Flycatcher (Tyrannus savana). Some noteworthy occurrences of rare to uncommon species were influenced by weather events. Using current data in conjunction with past records, published and unpublished, we assess changes in the status of avian species on St. Croix with respect to site-specific environmental changes. Although documented changes in the status of birds on St. Croix were sometimes the result of increased observer effort, some changes in species status were real. Some real positive changes were associated with a general increase in rainfall over the past decade. Avian species that increased in abundance and distribution since 2002 include eight waterbirds, one resident columbid, two partial migrant columbids, and one migrant parulid. While we found no clear evidence of any negative declines since 2002, species that showed a negative decline since the 1980s include one migrant larid, and three migrant landbirds, all forest species. Keywords: breeding, conservation, distribution, landbirds, St. Croix, waterbirds, wetlands Resumen: Registros y observaciones de aves acuáticas nidificantes, aves raras y poco comunes e individuos marcados en St. Croix, Islas Vírgenes de los Estados Unidos—La continuación de los muestreos de aves a largo plazo realizados en St. Croix, Islas Vírgenes de los Estados Unidos, desde agosto de 2004 hasta julio de 2012 (8 años) dio como resultado nueva información sobre 87 especies, 67 de las cuales son raras o poco comunes. Sin embargo, nuestro énfasis está en la documentación sitio-específica de 16 especies de aves acuáticas nidificantes raras y comunes y de 3 colúmbidos. También proporcionamos documentación para individuos de 10 especies de aves acuáticas y 1 falconiforme marcados en América del Norte, América del Sur o el Caribe que fueron vistos o recuperados en St. Croix. Cuatro individuos de dos de estas especies (Numenius phaeopus y Arenaria interpres) migraron a St. Croix más de una vez. Documentamos completamente las especies de aves transitorias vagrantes raras que se han registrado en St. Croix menos de 10 veces y las especies raras a poco comunes que de otro modo son de interés histórico. Incluimos cinco especies desconocidas previamente en St. Croix: Calidris ferruginea, Larus marinus, Coccyzus erythropthalmus, Crotophaga major y Tyrannus savana. Algunas ocurrencias notables de especies raras a poco comunes fueron influenciadas por eventos climáticos. Utilizando datos actuales junto con registros pasados, publicados y no publicados, evaluamos los cambios en el estado de la avifauna de St. Croix con respecto a los cambios ambientales sitio-específicos. Aunque los cambios documentados en el estado de la avifauna de St. Croix fueron en ocasiones el resultado de un incremento en el esfuerzo de observación, algunos de estos cambios fueron reales. Algunos cambios positivos reales se asociaron con un aumento general de las precipitaciones en la última década. Las especies de aves que aumentaron en abundancia y distribución desde 2002 incluyen ocho aves acuáticas, un colúmbido residente, dos colúmbidos migratorios parciales y un parúlido migratorio. Aunque no se encontraron pruebas claras de un decline negativo desde 2002, las especies que mostraron una disminución negativa desde la década de 1980 incluyen un lárido migratorio y tres aves terrestres migratorias, todas ellas especies de bosque. Palabras clave: aves acuáticas, aves terrestres, conservación, distribución, humedales, nidificación, St. Croix Résumé: Mentions et observations d’oiseaux d’eau nicheurs, d’oiseaux rares et peu communs et d’individus marqués à Sainte-Croix (Îles Vierges américaines)—La poursuite de l’étude à long terme de l’avifaune de Sainte-Croix (Îles Vierges américaines), d’août 2004 à juillet 2012 (8 ans) a fourni de nouvelles informations sur 87 espèces, dont 67 rares à peu communes. Nous avons toutefois mis l’accent sur la documentation à l’échelle des sites pour 16 oiseaux d’eau nicheurs, rares à communs, et trois colombidés. Nous fournissons également des informations sur 10 espèces d’oiseaux d’eau et une espèce de faucon dont des individus marqués en Amérique du Nord, en Amérique du Sud ou dans les Caraïbes ont été contrôlés ou repris à Sainte-Croix. Quatre individus de deux de ces espèces (Courlis corlieu (Numenius phaeopus) et Tournepierre à collier (Arenaria interpres)) ont migré plus d’une fois jusqu’à Sainte-Croix. Nous documentons entièrement les espèces vagabondes et rares observées moins de 10 fois à Sainte-Croix et les espèces rares à peu communes présentant un intérêt historique. Nous mentionnons cinq espèces jusqu’alors inconnues à Sainte-Croix : le Bécasseau cocorli (Calidris ferruginea), le Goéland marin (Larus marinus), le Coulicou à bec noir (Coccyzus erythropthalmus), l’Ani des palétuviers (Crotophaga major) et le Tyran des savanes (Tyrannus savana). Certaines apparitions remarquables d’espèces rares à peu communes étaient liées à des événements météorologiques. En utilisant les données actuelles en conjonction avec des données antérieures, publiées et non publiées, nous évaluons les changements du statut des espèces d’oiseaux à Sainte-Croix par rapport à des changements environnementaux à l’échelle des sites. Bien que les changements documentés du statut des oiseaux à Sainte-Croix soient parfois liés à une augmentation de l’effort d’observation, certains d’entre eux sont bien réels. Des changements positifs réels peuvent être associés à une augmentation générale des précipitations au cours de la dernière décennie. Parmi les espèces d’oiseaux dont l’abondance et la répartition ont augmenté depuis 2002, se trouvent huit oiseaux d’eau, un colombidé présent toute l’année, deux colombidés partiellement migrateurs et une paruline migratrice. Bien que nous n’ayons trouvé aucune preuve manifeste de déclin négatif depuis 2002, les espèces qui ont affiché un déclin négatif depuis les années 1980 comprennent un laridé migrateur et trois espèces forestières terrestres migratrices. Mots clés: conservation, oiseaux d’eau, oiseaux terrestres, répartition, reproduction, Sainte-Croix, zones humides
Studies of migratory and resident shorebirds in Venezuela have been mainly
concentrated in the western Caribbean islands and at some interior wetlands of
Venezuela. However, the wetlands of the central coastal region of Venezuela also
support signiicant communities of resident and migratory shorebirds,
particularly Laguna de Tacarigua. In this study we assess the abundance and
species richness of migratory and resident shorebirds, in relation to variation in
the water depth of their foraging areas in a narrow channel between mangroves
at Laguna de Tacarigua between May 2008 and April 2009. We recorded an
aggregate of 783 individuals of 14 shorebird species during eight monthly
counts along a 3-km long transect. Eleven species were trans-hemispheric
migrants, and three were intra-tropical migrants with resident populations. The
occurrence of these birds at Laguna de Tacarigua was determined by the water
depth in the foraging areas.
Avocets wintering on the Guerande peninsula have a daily cycle unusual among intertidal shorebirds: they roost during the day on the intertidal mud and feed at night on the salt-marshes. The authors study the diet of these shorebirds as well as the characteristics of the saltpans used during nocturnal feeding. Avocets seek mainly Chironomidae larvae and polychete worms, and favour 'water-stocking' basin and evaporation saltpans which are not used for salt production (water depth between 2 and 15 cm). The nocturnal feeding is analysed using the 'preference' hypothesis, i.e. that avocets 'prefer' saltpans as the sediment is more favourable to the development of their prey, and feed at night because of lower disturbance level and potential higher prey activity.
Many birds move at night, and although there is strong potential for collisions with stationary structures, the behavior of birds in response to such structures is poorly understood. We studied the nocturnal interactions of waterbirds with a 550v transmission powerline in the flat, open landscape of the Florida Everglades using a combination of surveillance radar to detect incoming birds, and night vision optical equipment to observe flight behavior. During 118 hours of observation we recorded a total of 285 flocks of ciconiiform birds crossing the powerline during spring 1997. We visually observed 663 birds in 187 flocks, and documented their response to the powerline. We found that the flight directions and the colony site locality strongly suggested regular nocturnal foraging behavior of some species, especially Black-crowned Night Herons (Nycticorax nycticorax) and Wood Storks (Mycteria americana). Birds flying at night were less likely to react to the powerline, suggesting that powerlines may pose more of a collision threat during darkness. However, we also found that waterbirds flew higher at night than during the day and thus came into a zone of potential contact with the powerline much less often than during the day.
We studied nocturnal and diurnal behavior of breeding American Avocets (Recurvirostra americana) at the Jay Dow, Sr. Wetlands in the northwestern Great Basin, USA. Seven-day observation periods were centered on two full moons when ambient light was maximal and auxiliary lighting unnecessary. We recorded avocet density, habitat use, interbird distances, and behavior three times daily (beginning at 07:00, 15:00, 23:00 PST) for 14 days. We calculated the mean proportion of individuals within flocks engaged in four behavior classes (foraging, copulating, agonistic, other). Foraging birds were further subdivided by technique (pecking, dunking, scything). Avocets copulated with similar frequencies during the morning, afternoon, and night. Avocets were more aggressive and closely spaced at night than during day. The full repertoire of behaviors seen during daylight also occurred at night, though frequencies of particular behaviors, flock location, and interbird distances varied among morning, afternoon, and nighttime observations. The role of nocturnal reproductive behavior should be assessed in species generally perceived as being diurnal.
differed between day-time and night-time and varied with the presence and absence of moonlight, depending on the behavioural status (territorial or non-territorial) of individuals, their foraging strategy (visual or tactile), and types and abundance of available prey. Territorial Willets were visual foragers when feeding on fiddler crabs (Uca cumulanta) on sand-mud substrata, both by day and on moonlit nights. Territorial Willets, on moonless nights, and non- territorial ones, during all light conditions, foraged tactilely on soft or liquid mud habitats. G. Rompr & R. McNeil, Dpartement de sciences biologiques, Universitde Montreal, C.P. 6128, Succ. "Centre-ville", Montreal, Quebec, Canada H3C 3J7.
We examine foraging behavior of coastal black bears (Ursus americanus kermodei) during different light regimes on a salmon stream in British Columbia, Canada (2000-2002). Bears (maximum 7 simultaneously) were primarily active during daylight near the onset of the salmon spawning run and shifted to twilight and darkness as the spawning run progressed. Overall time budget included search and pursuit (58%), handling and ingestion (38%), and agonistic interactions with other bears (4%). Scavenging was greatest during daylight (19%) and lowest during darkness (3%). Bears were most efficient at capturing live salmon when standing (35.4% success) followed by running (20.5%) and walking (15.2%). Highest capture efficiency Occurred during twilight (33.6%) compared with daylight (26.5%) and darkness (24.7%). Capture rate ranged from I to 3 salmon per hour per bear, Our results suggest that bears increased their total salmon intake by alternate use of visual and auditory cues during daylight and darkness.
Investigations of day and night abundance and foraging activity of several shorebird and waterfowl species in the western
Jade Bay had previously shown that their abundance did not differ between day and night but the proportion actively foraging
was significantly higher at night, especially in surface feeders, such as plovers, Dunlins, Common Redshanks, Pied Avocets,
Shelducks and Mallards. Foraging activity patterns in shorebirds are greatly affected by the behaviour and availability of
their benthic prey, but quantitative data on day-night activity of intertidal invertebrates are scarce. Therefore in this
study we determined activity patterns and availability of benthic prey species (i) by different sampling methods and (ii)
by visual observations of macrozoobenthic organisms during day and night from April to June 2004. Sampling showed that the
abundance and biomass of macrozoobenthic organisms was similar during both day and night. But visual observations showed significantly
greater numbers of the polychaetesHediste diversicolor andHeteromastus filiformis at the surface by night than by day suggesting that polychaetes may be more available to shorebirds at night. In addition
two sampling methods, the generally used corer and the sediment-plane (described byDesholm et al. 1998) were compared for their ability to determine the vertical distribution of benthic organisms. Sediment-plane
samples showed a significantly higher abundance of vertically mobile polychaetes in the uppermost layer than the core samples.
This indicates that the sediment-plane is a better and more accurate means of recording the density of benthos communities
in the uppermost sediment layers than the corer, because the polychaetes are not able to escape into deeper mud. However,
the best method for determining the availability of macrozoobenthic prey for surface feeding birds would appear to be direct
observation of surface activity.
In Bahia Samborombon (SW Atlantic; 35°30′–36°22′S; 56°45′–57°23′W) migratory American golden plover (Pluvialis dominica), black-billed plover (P. squatarola), ruddy turnstone (Arenaria interpres), and whimbrel (Numenius phaeopus) forage on fiddler crabs (Uca uruguayensis). These shorebirds have distinct patterns of feeding behavior and capture different proportions of each sex and size. P. dominica made short runs, capturing mostly juvenile crabs, which are eaten whole. P. squatarola use a similar feeding strategy but capture females primarily. A. interpres walks continuously, capturing almost exclusively large male crabs (71%). N. phaeopus walk in the Uca patch and probe burrows by inserting the bill; they primarily capture females. The feeding rate of A. interpres is higher than that of P. dominica, P. squatarola, and N. phaeopus. Handling time shown by P. dominica and A. interpres was greater than the other two species for all categories of crabs. In all cases, handling time of male crabs was greater
than those of either females or juveniles. All the evidences suggest that U. uruguayensis is an important food source for all these species and should be accounted in any conservation endeavor. *** DIRECT SUPPORT
*** A01BY085 00006
Fiddler crabs (Uca sp.) provide a good example of prey whose antipredator behaviour places them in a ‘waiting game’ contest with their predators. After visually detecting an approaching predator, fiddler crabs typically retreat into a burrow. When this occurs, a crab must decide how long to wait for the predator to depart before re-emerging and potentially exposing itself to attack. Similarly, the predator must decide how long to wait for the crab to re-emerge before departing in search of other foraging opportunities. Hugie (2003, Behavioral Ecology,14, 807–817) recently presented an analysis of such a predator–prey waiting game. The model makes various predictions, including ones about the general shape of each player's waiting distribution (the distribution of waiting times one would expect to observe for individuals in that role). I present an empirical test of the waiting game during interactions between the black-bellied plover, Pluvialis squatarola, and the fiddler crab Uca princeps. As predicted by the model, the plovers' waiting distribution resembled a negative exponential function, whereas the waiting times of crabs were more variable and followed a positively skewed distribution. As further predicted, very little overlap occurred between the two players' waiting distributions and plovers rarely outwaited crabs. I conclude that the waiting decisions of the black-bellied plover and U. princeps support the general predictions of Hugie (2003) and result from a predator–prey waiting game.
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