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“Replacements” of Landbird Species on Socorro Island, Mexico
Abstract
The endemic dove Zenaida graysoni of Socorro Island, an oceanic island in the Pacific south of Baja California, became extirpated between 1958-1978, and the endemic mockingbird Mimodes graysoni diminished during the same years and was approaching extinction by 1981. The mainland mourning dove Z. macroura became established on Socorro between (probably) 1971-1978, and the mainland northern mockingbird Mimus polyglottos between 1978-1981. Extermination of the endemics was probably caused by predation by feral cats Felis catus introduced in 1957 or later. There is no evidence of any actual competition between the pairs of species, and their preferred habitats overlap only slightly. The nearly concurrent establishment of the two invading species, known to have occurred frequently as casual visitors to Socorro and other islands, is attributed largely to the provision of fresh water made available as a result of human settlement.-from Authors
... The avifauna of the Revillagigedo Islands, particularly that of Socorro, has been the subject of several studies addressing taxonomy, status, and biogeographic relationships (Anthony, 1898;McLellan, 1926;Brattstrom & Howell, 1956;Jehl & Parkes, 1982;Stone, 1986;Brattstrom, 1990;Wehtje et al., 1993). Formed in the late Tertiary, the islands have always been isolated from the mainland (Fig. 1), leading to interesting evolutionary processes for the terrestrial animals and plants (Johnston, 1931;Gentry, 1949;Brattstrom, 1953Brattstrom, , 1990Jehl & Parkes, 1983;Levin & Moran, 1989;Jimenez, 1991 At the present time, Socorro Island contains eight endemic taxa of terrestrial birds (one genus and seven subspecies): yellow-crowned night heron Nyctanassa violacea gravirostris, Socorro red-tailed hawk Buteo jamaicensis socorroensis, Socorro ground dove Columbina passerina socorroensis, green parakeet Aratinga holochlora brevipes, Socorro wren Thryomanes sissonff, Socorro mockingbird Mimodes graysoni, tropical parula Parula pitiayumi graysoni, and Socorro towhee Pipilo erythrophthalmus socorroensis. Two other endemic taxa, the Socorro dove Zenaida graysoni and elf owl Micrathene whitneyi graysoni, are believed to be extirpated from the island. ...
... The mourning dove Zenaida macroura arrived around 1958, and the northern mockingbird Mimus polyglottos became established in 1978. Apparently their colonization was favored by human activities and increasing populations of introduced sheep, both of which have created a habitat suitable for avian colonization (Jehl & Parkes, 1983). One marine bird species not discussed here is Townsend's shearwater Puffinus auricularis, which is endemic to the archipelago (Jehl, 1982;Santaella & Sada, 1991). ...
... The increasing island distribution of the northern mockingbird and the potential effect of competition between this species and the endemic mockingbird should be reviewed. Jehl and Parkes (1983) found that Socorro and northern mockingbirds used different habitats: 'Only once, in 1978, did we see a Northern Mockingbird in the habitat of the Socorro Mockingbird'. In 1990-1992, we found the northern mockingbird in every disturbed forest site. ...
Socorro Island supports the highest plant and animal diversity of the Revillagigedo Islands. Eight endemic terrestrial bird species (one endemic genus and seven endemic subspecies) currently are present on the island. One endemic species is now extinct and the status of another endemic subspecies is uncertain. Forty visiting species (both seasonal and accidental) represent the non-endemic terrestrial avifauna of the island. In this work, we present quantitative data on the abundance and density of the endemic avifauna and on the degree of habitat disturbance on Socorro Island. We found that plant species richness, plant density, and number of vegetative strata in the less disturbed areas to be positively related to bird density. The simple community structure and fragile island ecosystem are now threatened by several factors including sheep overgrazing, erosion, predation by feral cats, and human disturbance. Therefore, we propose that the island be protected by means of an integratedresource management plan and be designated as a legally protected area. Five management strategies are needed immediately. Finally, we propose to work jointly with Mexican military personnel to manage, improve, and preserve the ecosystems of Socorro Island.
... Such a negative impact of novel competitors is likely to be similar, regardless of if their origin is due to anthropogenic causes or natural colonization (Nackley et al. 2017). One factor that may contribute to the pressure on incumbent insular species is that islands rarely provide alternative habitats suitable for endemic species to shift their population ranges to in order to minimize competition with new colonizers (Jehl andParkes 1983, Vilà andHulme 2017). ...
... In this study, our main objective was to unveil the possible impact of the recent establishment and expansion of a breeding population of Sardinian Warbler on the densities of its congeners, Cyprus and Spectacled Warblers, with much longer established breeding populations in Cyprus, in the light of previous work on competition and turnover of species on islands (Mayr 1965, Jehl and Parkes 1983, Dhondt 2012, Bellard et al. 2016, Hoffmann and Courchamp 2016, Wilson et al. 2016. Through this study we aimed to quantify population densities and dynamics in different areas, habitat types, and across seasons. ...
Many island endemics around the world have evolved from populations of colonists. Further colonizations may lead to interactions between older and newer colonists. Little is known, however, regarding the impact of more recent island colonizers on incumbent congeners, partly because of a dearth of examples of natural colonizations in the recent past. Sardinian Warbler (Sylvia melanocephala) recently colonized Cyprus and has rapidly expanded its breeding range. We examined the impact of the Sardinian Warbler colonization on the endemic Cyprus Warbler (S. melanothorax) and on another congener, the Spectacled Warbler (S. conspicillata). We performed 402 population surveys in 32 sample plots across the island, covering five different habitat types and variation across three seasons. Our results show that Cyprus Warbler has undergone a significant decline during the five years of the study, especially in disturbed habitats, while Sardinian and Spectacled Warbler populations have remained stable. Although the longer established Spectacled Warbler clearly segregated habitat with Cyprus Warbler, Sardinian Warbler numbers were negatively associated with Cyprus Warbler abundance, suggesting its presence may contribute to the endemic’s decline. Maquis scrub was favored by both Cyprus Warbler and Sardinian Warbler, but the latter also occurred in high densities in disturbed habitats. The colonizer’s prevalence in disturbed, mixed habitat, suggests it may replace the endemic in parts of its former range following anthropogenic perturbations. Natural colonizations may contribute to rapid population declines in island endemics in a similar way to introduced species, especially when combined with strong effects of habitat disturbance.
... Often, primary prey is determined by relative abundance (Van Aarde 1980;Veitch 1985). Predation by cats has been directly responsible for numerous island extinctions of mammals (Mellink 1992;Tershy et al. 2002), reptiles (Iverson 1978;Mitchell et al. 2002), and birds ( Jehl & Parks 1983;Lever 1994;Dowding & Murphy 2001;Veitch 2001). ...
... Such examples lend support to the idea that only a few predators can have substantial impacts on prey demography and community-level processes (Estes et al. 1998;Roemer et al. 2001;Roemer et al. 2002). A more recent case of wild extinction occurred in Socorro Island (Mexico), where an endemic species of dove (Zenaida graysoni) disappeared in the wild and the population of an endemic passerine (Mimodes graysoni) was reduced nearly to extinction after cats were introduced by a military garrison in the late 1950s ( Jehl & Parks 1983;Martínez & Curry 1996). ...
Feral cats are directly responsible for a large percentage of global extinctions, particularly on islands. We reviewed feral cat eradication programs with the intent of providing information for future island conservation actions. Most insular cat introductions date from the nineteenth and twentieth centuries, whereas successful eradication programs have been carried out in the last 30 years, most in the last decade. Globally, feral cats have been removed from at least 48 islands: 16 in Baja California (Mexico), 10 in New Zealand, 5 in Australia, 4 in the Pacific Ocean, 4 in Seychelles, 3 in the sub-Antarctic, 3 in Macaronesia (Atlantic Ocean), 2 in Mauritius, and 1 in the Caribbean. The majority of these islands (75%; n= 36) are small (≤5 km²). The largest successful eradication campaign took place on Marion Island (290 km²), but cats have been successfully removed from only 10 islands (21%) of ≥10 km². On Cousine Island (Seychelles) cat density reached 243 cats/km², but on most islands densities did not exceed 79.2 cats/km² (n= 22; 81%). The most common methods in successful eradication programs were trapping and hunting (often with dogs; 91% from a total of 43 islands). Frequently, these methods were used together. Other methods included poisoning (1080; monofluoracetate in fish baits; n= 13; 31%), secondary poisoning from poisoned rats (n= 4; 10%), and introduction of viral disease (feline panleucopaenia; n= 2; 5%). Impacts from cat predation and, more recently, the benefits of cat eradications have been increasingly documented. These impacts and benefits, combined with the continued success of eradication campaigns on larger islands, show the value and role of feral cat eradications in biodiversity conservation. However, new and more efficient techniques used in combination with current techniques will likely be needed for success on larger islands.
... In some instances, observations that seem consistent with a general theory turn out, upon close examination, to have a very different genesis. For example, the endemic dove Zenaida graysoni of Socorro Island disappeared between 1958 and 1978, while the population of the endemic mockingbird Mimodes graysoni dwindled rapidly towards extinction at exactly the same time (Jehl & Parkes 1983). Approximately during the same period, the mainland Mourning Dove Z. macroura and mainland Northern Mockingbird Mimus polyglottos established resident populations on the island. ...
... The dogma is that stronger mainland species readily replace weaker island ones, and the theory is the dynamic equilibrium theory of island biogeography, in which extinction must balance immigration to maintain species richness (MacArthur & Wilson 1967). This interpretation would be greatly in error on both counts (Jehl & Parkes 1983). Predation by newly introduced feral cats probably caused the decline of both endemics. ...
It has not been established that a major cause of extinction in birds or any other taxa is failure of metapopulation dynamics: the collapse of a network of ephemeral but discrete populations as movement between them becomes increasingly infrequent. The few data on who goes where and who mates with whom suggest that most species are structured as either a single large population or a small set of source populations and a larger set of sinks. The extinction of the latter is irrelevant to the persistence of the species. However, regional decline of a species in the face of habitat destruction and fragmentation can mimic a failure of metapopulation dynamics, because distinct aggregations of individuals will disappear much as they would if populations in an interacting network were eliminated one by one. Any species with highly restricted range is at great risk of extinction from spatially localized forces, such as cyclones or deforestation. Restricted range rather than inherent weakness is the main reason that so many island species have gone extinct or are endangered. Species with small populations in contact with much larger heterospecific ones with which they are interfertile are threatened with extinction by hybridization. Finally, the disappearance of a species from a site may be due to subtle habitat change, even if this observation seems superficially consistent with some general population theory, such as the dynamic equilibrium theory of island biogeography. Current theory is an inadequate substitute for intensive field studies as a means to address the conservation problems of individual species.
... Herbivores were introduced to these islands in different periods. Domestic sheep (Ovis aries) were brought to Socorro in 1869 [8]. Overgrazing by sheep facilitated the transformation into open and eroded habitats of a significant percentage of the forests and scrublands in the southeast half of the island [9]. ...
The Revillagigedo Archipelago, located in the Eastern Pacific Ocean, stands out for its unique biological richness and endemism. These islands remained uninhabited until the second half of the twentieth century, allowing a better conservation status than on other oceanic islands. However, the continuous introduction of potentially invasive alien plant species, and the lack of adequate control or eradication actions, jeopardize the conservation and restoration of these islands’ fragile ecosystems. We present the most complete vascular plant species inventory and an updated list of alien plant species of the Revillagigedo Archipelago, which was compiled through an extensive review of national and international plant collections and other sources. Our 272 species list includes 106 alien plant species (39.3%; 104 in Socorro, and 16 in Clarion): 67 (24.8%) are naturalized, 14 (5.2%) are casual aliens, and 25 (9.3%) subsist under cultivation. The documented alien species belong to 73 families. Annual and perennial herbs are the prevailing life forms in the alien flora, while naturalized species are primarily native to North America. The number of introduced species has increased significantly since the islands became inhabited. Many of the recently introduced species pose a major invasion risk like on other islands of the world.
... More than 16 million animals are estimated to be killed by cats each year in New Zealand, where there are no native mammals except for bats . Studies also show that at least 248 species, including mammals (Mellink, 1992;Tershy et al., 2002), reptiles (Iverson, 1978;Mitchell et al., 2002), and birds (Jehl & Parkes, 1983;Veitch, 2001), have been affected by the negative impacts of feral cats on 120 islands around the world Medina et al., 2011). For these reasons, many countries have attempted to eradicate and/or manage feral cats (Bester et al., 2002;Nogales et al., 2004;Veitch, 2001). ...
Feral cat management needs cooperation, including financial support, from a variety of stakeholders. We used a payment card approach to investigate the willingness of tourists to donate to non-lethal feral cat management at a potential natural World Heritage site on Amami Oshima Island in Japan. We found that more than 80% of tourists intended to donate funds to non-lethal feral cat management, and the mean willingness to donate was about USD $14 (1374.1 JPY). The rate of participation in the donation was higher than that found in previous studies, and the amount of intention to donate was large enough to support non-lethal cat management. Respondent income and attitudes toward lethal options affected intentions to donate. Those who valued the island farmland also had a higher intention to donate. Our findings provide useful information for the implementation of feral cat management strategies to conserve biodiversity while minimizing conflict.
... Oceanic islands are really relevant in the context of whole world biodiversity because harbor an important number of endemic species (Mac Arthur and Wilson 1967;Gorman 1979;Whittaker and Fernández-Palacios 2007). On its, feral cats have been directly responsible for the extinction of numerous mammals (Mellink 1992;Tershy et al. 2002), reptiles (Iverson 1978;Mitchell et al. 2002) and birds (Jehl and Parks 1983;Lever 1994;Veitch 2001). For this reason this predator is considered to be one of the 100 worst invasive species in the world (Lowe et al. 2000). ...
... Frequently, feral cats (Felis catus) have been introduced as pets or as an attempt to control rodent populations (Moran 1996, Van Aarde 1980). As a result, cats have been responsible for the extinction and extirpation of at least 10 bird and mammal species from Mexican islands , and at least 9 other mammals, 2 birds, and 1 lizard are under threat for the same reason (Álvarez-Castañeda and Ortega-Rubio 2003, Arnaud et al. 1993, IUCN 2011, Jehl and Parkes 1983, Mellink et al. 2002. ...
... In Socorro, an oceanic island located on the Revillagigedo Archipelago in the Mexican Pacific (Fig. 1), cats have been present since 1957. Jehl & Parkes (1983) con-sidered that this predator is responsible for the in situ extinction of the endemic Socorro dove (Zenaida graysoni). Cats are also a threat to the Socorro Blue Lizard (Urosaurus auriculatus; Arnaud et al., 1994), and Townsend's Shearwater (Puffinus auricularis; Llinas-Gutiérrez, 1994). ...
Socorro is an oceanic island rich in biodiversity and endemisms. However, the island has been threatened by feral cats since 1957. The diet of this predator, determined through the analysis of stomach contents of 79 cats, consisted mostly of house mice (Mus musculus, 22.16%), endemic lizards (Urosaurus auriculatus, 15.09%), anthropogenic rubbish (15.09%), and insects (Orthoptera, 13.20%). The home range of the feral cat was identified through telemetry using four individuals with GPS/VHF radio-collars. The three males had a much larger average home range of 219.10 ha, as compared with 118.86 ha of the female. Knowing the home range of the Socorro Island feral cat is critical for the successful eradication of the island's invasive population. Thanks to this information, it is possible to calculate the trapping effort and the amount of bait needed per unit area to successfully carry out the ongoing eradication, contributing to the conservation of global biodiversity.
... In Socorro, an oceanic island located on the Revillagigedo Archipelago in the Mexican Pacific (Fig. 1), cats have been present since 1957. Jehl & Parkes (1983) con-sidered that this predator is responsible for the in situ extinction of the endemic Socorro dove (Zenaida graysoni). Cats are also a threat to the Socorro Blue Lizard (Urosaurus auriculatus; Arnaud et al., 1994), and Townsend's Shearwater (Puffinus auricularis; Llinas-Gutiérrez, 1994). ...
Isla Socorro es una isla oceánica rica en biodiversidad y endemismos. Sin embargo, la isla ha sido impactada por el gato asilvestrado desde 1957. A través del análisis del contenido estomacal de 79 gatos se determinó la dieta de este depredador, la cual está constituida mayormente por el ratón doméstico (Mus musculus, 22.16%), la lagartija endémica (Urosaurus auriculatus, 15.09%), residuos antropogénicos (15.09%), e insectos (Orthoptera, 13.20%). Se identificó el ámbito hogareño de los gatos a través de telemetría, utilizando cuatro individuos con radio-collares GPS/VHF. El ámbito hogareño de los machos resultó de 219.10 ha en promedio, mucho mayor que el de las hembras que fue de 118.86 ha. Conocer el ámbito hogareño del gato asilvestrado de Isla Socorro es clave para la erradicación exitosa de la población de la isla. Gracias a esta información se ha podido calcular el esfuerzo de trampeo o la cantidad de carnada que deben ser empleadas por unidad de área durante la erradicación en curso, que es relevante para la conservación de la biodiversidad global.
... Del archipiélago de Revillagigedo se han publicado varios estudios enfocados a listados de aves (Anthony 1898, Brattstrom y Howell 1956, Jehl y Parkes 1982, 1983, Everest 1988, Howell y Webb 1989, 1990, Santaella y Sada 1991, Pitman y Ballance 2002, Wanless et al. 2009) y en ninguno de ellos se reporta la presencia de S. decaocto, por lo que este trabajo representa el primer registro en las islas Clarión y Socorro. ...
Registramos la presencia de Streptopelia decaocto en dos islas del archipiélago de Revillagigedo: isla Clarión e isla Socorro. Observamos
tres adultos de S. decaocto entre marzo y julio de 2015. En ambas islas las aves se encontraron asociadas a sitios con
actividad humana: en las instalaciones del destacamento militar de la Marina, Armada de México y en uno de sus buques. Se
requieren de más estudios que permitan evaluar la distribución, abundancia y efectos de S. decaocto en las islas de Revillagigedo.
... In Socorro, an oceanic island located on the Revillagigedo Archipelago in the Mexican Pacific (Fig. 1), cats have been present since 1957. Jehl & Parkes (1983) con-sidered that this predator is responsible for the in situ extinction of the endemic Socorro dove (Zenaida graysoni). Cats are also a threat to the Socorro Blue Lizard (Urosaurus auriculatus; Arnaud et al., 1994), and Townsend's Shearwater (Puffinus auricularis; Llinas-Gutiérrez, 1994). ...
Socorro is an oceanic island that has been affected by the presence of feral cats since 1957. The diet of this predator was determined through the analyses of stomach contents of 79 captured cats, which consisted of a higher percentage of house mice (Mus musculus) (22.16%), endemic lizards (Urosaurus auriculatus) (15.09%) and anthropogenic refuses (15.09%); it also fed largely on insects (Orthoptera) (13.20%). The home range of the cats was identified through telemetry, using four animals with radio-collars GPS/VHF. Males had an average home range of 219.10 ha, compared with 118.86 ha of the female. The range of the female H02 overlapped 100% with that of the male M06. Knowing the home range of the cats of Socorro Island will aid in the successful management of the species, since it will possible to calculate the trapping effort and the amount of bait needed per unit area to successfully carry out any conservation management plan.
... Del archipiélago de Revillagigedo se han publicado varios estudios enfocados a listados de aves (Anthony 1898, Brattstrom y Howell 1956, Jehl y Parkes 1982, 1983, Everest 1988, Howell y Webb 1989, 1990, Santaella y Sada 1991, Pitman y Ballance 2002, Wanless et al. 2009) y en ninguno de ellos se reporta la presencia de S. decaocto, por lo que este trabajo representa el primer registro en las islas Clarión y Socorro. ...
We recorded for the first time the presence of Streptopelia decaocto in two of the Revillagigedo islands; Clarion and Socorro. We observed three adults of S. decaocto on different dates between March and July 2015. On both islands, we observed the birds in areas associated with human activities: in the military base of the Mexican Navy and in a vessel of the Navy. Further studies are needed to assess the distribution, abundance, and effects of S. decaocto in the Revillagigedo Islands.
... Aunque en muchos de los casos de extinción de especies conocidos hasta la fecha no se dispone de información sobre los factores causantes, se estima en más de la mitad de los casos estarían involucradas especies invasoras, mientras que hasta un 20% de las extinciones parecen provocadas exclusivamente por la acción de especies invasoras (Clavero y García-Berthou, 2005 (Jehl y Parkes, 1983;Jehl y Everett, 1985;Aguirre-Muñoz et al., 2009); en estas islas, a menudo deshabitadas, la introducción de especies exóticas puede ser el principal factor de antropización ambiental (Reaser et al., 2007). Es destacable que, aunque en la mayoría de los casos no se llegue a la extinción total de una especie, la presencia de especies invasoras puede ser el detonante de la desaparición de poblaciones nativas, disminuyendo la diversidad local y alterando los procesos ecológicos y evolutivos en un proceso conocido como homogenización biótica, por el cual se produce un aumento en la similitud genética, taxonómica y funcional entre diferentes zonas o ecosistemas a lo largo de un periodo de tiempo determinado (Olden, 2008). ...
El estado de Michoacán incluye la región productora de aguacate Hass (Persea americana)
más importante a nivel nacional y mundial; sin embargo, esto ha generado una reducción
importante en la superficie forestal de bosques templados y por consiguiente, la pérdida
de biodiversidad. El objetivo de este estudio fue determinar la riqueza y abundancia de
aves en paisajes dedicados al cultivo de aguacate bajo dos condiciones de manejo; huertos
inmersos entre fragmentos remanentes de bosque (HAB) y en ausencia de estos (HA).
Con base a técnicas de censos poblacionales, búsqueda intensiva y captura con redes,
aplicadas a intervalos mensuales, en dos años consecutivos se registraron un total de 128
especies, de las cuales 118 (92%) fueron para HAB y 62 (48%) para HA, habiendo diferencias
significativas en la diversidad alpha de Fisher (15.4 para HA, y 23.8 para HAB).
La composición de las especies más abundantes varió entre tipos de huerta, siendo las
especies de HA más afines a zonas urbanas. Concluimos que las prácticas de manejo de
huertas que incluyan remanentes de bosque, son mejor alternativa no sólo para las aves
sino por los beneficios y servicios ambientales como control de plagas para mantener
huertas más saludables.
... En el Archipiélago Revillagigedo, ubicado en el Pacífico Mexicano, se presentan fuertes alteraciones en sus habitáis ocasionadas por actividades humanas y por las especies animales introducidas (Ortega et al., 1992). En Socorro, la mayor de las cuatro islas que integran el Archipiélago, durante los últimos 30 años se ha reducido la abundancia y distribución de algunas especies de aves, tal como el zenzontle de Socorro (Mimodes graysoni), la pardela (Puffinus auriculatus) y el pipilo (Pipilo erythrophtalmus socorroensis) (Castellanos y Rodríguez-Estrella, 1993;Jehl y Parkes, 1982), habiéndose extinguido la paloma de Socorro (Zenaida graysoni) entre 1958 y 1978 (Jehl y Parkes, 1983). Actualmente el tecolote enano endémico (Micrathene whitneyi graysoni) no ha sido avistado en las últimas expediciones realizadas y se teme también haya desaparecido. ...
Resumen Entre abril de 1988 y noviembre de 1990 se efectuaron recorridos en diferentes asociaciones vegetales y estratos altitudinales de Isla Socorro para conocer la distribución del gato, la cual parece estar en función de la distribución del ratón doméstico (Mus musculus) y las actividades humanas, concentrándose en las inmediaciones del Sector Naval. El análisis de 46 heces fecales colectadas durante 1990 principalmente en zonas de matorral de Crotón, pastizal inducido y en el Sector Naval, muestra que la dieta del gato según los porcentajes de ocurrencia, esta constituida por tres principales tipos de presa: insectos del Orden Orthoptera, el ratón doméstico y la lagartija azul (Urusaurus auriculatus). En menor porcentaje aparecieron las aves, siendo la tortolita (Columbina passerina) la más frecuente en las muestras. Nuestras observaciones indican que a pesar de que los gatos no son abundantes y su distribución no abarca más del 50% de la superficie isleña, existe la necesidad de erradicarlo, ya que representa un peligro real para las especies nativas, particularmente para la avifauna y la lagartija azul. Consideramos que para la erradicación del gato, la cacería y los trampeos intensivos son métodos adecuados, siendo riesgoso el uso de venenos y el control biológico.
... Aunque en muchos de los casos de extinción de especies conocidos hasta la fecha no se dispone de información sobre los factores causantes, se estima en más de la mitad de los casos estarían involucradas especies invasoras, mientras que hasta un 20% de las extinciones parecen provocadas exclusivamente por la acción de especies invasoras (Clavero y García-Berthou, 2005 (Jehl y Parkes, 1983;Jehl y Everett, 1985;Aguirre-Muñoz et al., 2009); en estas islas, a menudo deshabitadas, la introducción de especies exóticas puede ser el principal factor de antropización ambiental (Reaser et al., 2007). Es destacable que, aunque en la mayoría de los casos no se llegue a la extinción total de una especie, la presencia de especies invasoras puede ser el detonante de la desaparición de poblaciones nativas, disminuyendo la diversidad local y alterando los procesos ecológicos y evolutivos en un proceso conocido como homogenización biótica, por el cual se produce un aumento en la similitud genética, taxonómica y funcional entre diferentes zonas o ecosistemas a lo largo de un periodo de tiempo determinado (Olden, 2008). ...
... Otro factor que puede llegar a influir y que se ha registrado en palomas, es la depredación de huevos y pichones por animales silvestres (Murton et al. 1974. La depredación por animales domésticos no debe ser subestimada pues en el paisaje rural hay presencia de perros y gatos que pueden llegar a influir en el tamaño poblacional como sucedió con Zenaida graysoni (Jehl & Parkes 1983). Aunque no se han hecho mediciones de densidad poblacional para L. conoveri, los TABLA 3. Nidos de L. conoveri encontrados en la vereda La Cascada durante el año 2004. ...
The Tolima Dove is a Colombian endemic, considered a threatened species due to its restricted distribution and the loss of its habitat; studies on habitat use do not exist. Our objective was to identify and characterize the habitat use of a population of L. conoveri in the river canyon Combeima (Tolima); six monitoring stations were established where extended point counts with variable radiuses/radii and a plant characterization on plots of 1000m2 were developed. Foraging, nesting, and perching were associated to plant variables through Canonical Correspondence Analysis (CCA). It was found that the dove feeds on seeds of Trompeto (Bocconia frutescens), a shrub typical of disturbed areas and a high frequency in the study area. The species used open areas for the foraging, this behavior showed an inverse relationship with secondary forest. For the nesting, the dove uses coffee trees, shrubs, and isolated weedy bushes near human housings, this behavior showed direct correspondence with the shrub. L. conoveri survives in degraded places and rural landscapes with sectors of dense undergrowth and abundant supply of seeds.
... The overall anticipated effect is a net benefit to the island ecosystem. This prediction is based on documented cases of widespread damage, including numerous extinctions, caused by introduced feral cats on islands (Aquirre et al. 2008;Dowding and Murphy 2001;Iverson 1978;Jehl and Parks 1983;Keitt et al. 2005;Lever 1994;Mellink 1992, Mitchell et al. 2002Nogales et al., 2004;Tershy et al., 2002;Veitch 2001) and follow-up studies that document the recovery of island species after cats have been removed (Keitt et al. 2002;Keitt and Tershy 2003;Nogales et al., 2004;Ratcliffe et al. 2010). The positive impacts expected on Floreana will primarily be the reduction in mortality of native and endemic island species including, but not limited to, the IUCN-listed Galápagos petrel, medium tree finch and Galápagos martin. ...
... The feral cat (Felis catus) is among the world's worst invasive alien species (Lowe et al. 2004). Its presence on islands has been recognized as one of the main causes of extinction of insular species (e.g., Jehl and Parkes 1983, Mellink 1992, Veitch 2001. Cats on islands have contributed to the extinction of 33 mammals, birds, and reptiles worldwide , Medina et al. 2011. ...
Guadalupe Island, off the Baja California peninsula, México, hosts the most important growing Laysan
Albatross (Phoebastria immutabilis) breeding colony in the eastern Pacific. Since this seabird’s first arrival in 1983, it has been affected by predation from feral cats (Felis catus), present on Guadalupe since the late 19th century. Heavy predation events have been recorded on the island, so we initiated a feral cat control campaign in 2003 and began collecting baseline information for developing an eradication plan. At the same time, we conducted seasonal monitoring of Laysan Albatross reproductive success in order to assess the benefits from control activities. Cat relative abundance on Guadalupe was estimated through spotlight surveys, and control was done at the southernmost end of the island around the 2 locations where Laysan Albatross nest: Colinas Negras and Punta Sur. Laysan Albatross population growth rate was calculated based on the number of reproductive individuals, while breeding success was estimated as the proportion of laid eggs that resulted in fledged chicks. A total of 203 cats were removed from the south end of Guadalupe between 2003 and 2013. During this same period, high reproductive success (0.8) was recorded for Laysan Albatross, suggesting a positive effect of cat control activities. We found significant differences in reproductive success between years with predation and no predation by feral cats. The Laysan Albatross colony on Guadalupe has grown steadily during the past 30 years, increasing from 4 to 143 breeding pairs between 1984 and 2013, respectively, and with a population growth rate of 1.10 between 2004 and 2013.
... Kingdon (1990) examined dispersal capabilities in some 20 avian families of birds and concluded that pigeons are the most effective colonists. They occur in oceanic islands off Africa (Kingdon 1990), Ecuador (Grant & Grant 1979), Mexico , Jehl & Parkes 1983, Europe (Bannerman & Bannerman 1966), as well as in Micronesia, Macronesia, New Guinea and surrounding islands (Beehler et al. 1986, Pratt et al. 1987. ...
To commemorate the sesquicentennial of Charles Darwin's "On the Origin of Species by Means of Natural Selection", we address an essential topic in this publication. Domestic pigeons were extremely important in shaping Darwin's theory of evolution: pigeons featured prominently not only in his "Origin of Species", but also in his treatise on "Variation under Domestication", in his "Descent of Man" and finally in his "Expression of Emotions". Darwin saw the process of domestication as solid evidence demonstrating the power of selection. He argued convincingly that all domestic pigeon breeds (some 150 in his day) descended from one ancestral species, the Rock Dove (Columba livia), and that from this single species, humans selected directionally for colors, sizes, shapes, peculiarities of bill shape and length, plumage characteristics and voice qualities. While these domestic races achieved remarkable morphological differentiation under selection in the course of human generations, extant genera of pigeons (Columbiformes) have attained similar traits during the course of natural selection in the wild. We present a comparison of such characters between modern domestic breeds of the Rock Dove, the original Darwin's Pigeons plus new breeds, and wild pigeon species to encourage further studies on their evolution in the light of molecular techniques not available at Darwin's time.
... Ground-feeding birds also formed the majority of birds eaten by cats in a mainland forest (Fitzgerald & Karl 1979) and on Stewart Island (Karl & Best 1982). On Socorro Island, off the Mexican coast, feral cats have exterminated the endemic dove and mockingbird, and reduced the numbers of the towhee (all ground-feeders), although tree-dwelling species remain common (Jehl & Parkes 1983). Nesting petrels also suffered very heavy predation on Herekopare Island and the susceptibility of the different species was probably influenced by their size and the timing of breeding. ...
House cats (Felis catus) were introduced to Herekopare Island, a mammal-free island of about 28 ha near Stewart Island, in about 1925. In winter 1970, the total population of 33 cats (20 males, 13 females) — a density of 1.2 cats/ha — was killed, mainly by trapping. Examination of stomach contents and scats showed that the cats fed mainly on petrels, supplemented by land birds and insects. The bird life of Herekopare Island was studied by H. Guthrie-Smith in 1911, L. E. Richdale in the early 1940s, and by New Zealand Wildlife Service staff in 1968 and 1970. Their accounts indicate that a vast breeding population of diving petrels and thousands of broad-billed prions were probably exterminated by the cats, though fairy prions and sooty shearwaters persisted. Among land birds, the yellow-crowned parakeet, robin, fernbird, brown creeper, Stewart Island snipe, and banded rail were exterminated. Two other species, the red-crowned parakeet and tomtit, probably disappeared but subsequently recolonised the island. Although cats had the greatest influence on the bird life over this period, wekas, which were present for some years, together with changes in the vegetation, may have affected some bird populations.
... Rats also can depredate bird nests, mainly those in burrows, but also those high in trees (Atkinson 1985, Fitzgerald et al. 1991) and have been reported as egg predators for the Blue-crowned Parrot (Aratinga acuticaudata neoxena) on Margarita Island (Rojas-Suárez 1994b). It is obvious that cats and rats can contribute considerably to population declines, and even extinction, of island bird species (Jehl and Parkes 1983, Fitzgerald 1988, Diamond 1989, Fitzgerald et al. 1991, Martínez and Curry 1996, Dowding and Murphy 2001, Nogales et al. 2003. ...
The Yellow-shouldered Parrot (Amazona barbadensis) has a disjunct geographical distribution and the smallest population of the species inhabits La Blanquilla Island in the southern part of the Caribbean Sea. We conducted field work from 1993 to 1998 to gather information on the natural history and population status of this parrot on La Blanquilla. We compared that information with similar data gathered previously from Margarita Island. We found three communal roosts on La Blanquilla and estimated the parrot population to be similar to 100 individuals. We found an average of 8.8 +/- 3.6 active nests/year; all nests were in the central and western parts of the island, mainly in tree cavities of Guaiacum officinale. Nests on La Blanquilla Island were closer to the ground than nests on Margarita Island. The breeding season on La Blanquilla Island started later and clutch size was lower (2.24 +/- 0.95 eggs/nest) than on Margarita Island. Parrots were observed foraging on 12 plant species; most observations involved consumption of the fruit of Casearia tremula (Flacourtiaceae). The main threats to Yellow-shouldered Parrots on La Blanquilla are predation and illegal poaching. Survival of the Yellow-shouldered Parrot on La Blanquilla Island is uncertain because of small population size and increasing threat levels.
... Mosquitoes are the principal vectors of avipoxes (Hansen 1999). Two columbid species currently exist on Socorro Island: the Socorro Ground Dove Columbina passerina socorrensis, an endemic subspecies that exists in small numbers at lower elevations throughout the island (Wehtje et al. 1993), and the Mourning Dove, a migratory species that was not recorded on Socorro Island prior to 1978 but has since become established (Jehl and Parkes 1983). The Mourning Dove and Socorro Dove are genetically closely related (Johnson and Clayton 2000). ...
To assess the potential disease risks posed by resident Columbiformes to the reintroduction of the Socorro Dove Zenaida graysoni to Socorro Island, Mexico, the endemic Socorro Ground Dove Columbina passerina socorrensis and the recently arrived Mourning Dove Zenaida macroura, were screened for ecto- and endoparsites, haemosporidia, Trichomonas gallinae, Chlamydophila psittaci and avian pox. All of the Mourning Doves and Socorro Ground Doves sampled appeared healthy upon capture. We detected Haemoproteus spp. in 88% of Mourning Dove and 30% of Socorro Ground Dove samples using microscopy. Two polymerase chain reaction (PCR) DNA amplification methods detected either Haemoproteus spp. or Plasmodium spp. Pooling results from both tests yielded positives in 100% of the Mourning Doves and 52% of the Socorro Ground Doves. A nested PCR detected Leucocytozoon spp. in 94% of the Mourning Doves and 61% of the Socorro Ground Doves sampled. Thus, at least two genera of haemosporidia are present in columbids of Socorro Island. Microscopy for T. gallinae yielded positives in 33% of Mourning Dove and 30% of Socorro Ground Dove samples. C. psittaci was not detected using PCR on either cloacal swab samples or tissue samples from tested Mourning Doves or Socorro Ground Doves. Necropsies revealed neither lesions indicative of the wet form of avian pox, nor internal lesions associated with trichomoniasis. These results suggest that Socorro Doves selected for reintroduction should be screened carefully to evaluate potential immunological challenges by native haemosporidians and to avoid introduction of other diseases apparently absent from native Columbiformes on Socorro Island.
... A particularly well-known exam- ple is that of the Stephens Island wren Xenicus lyalli , the entire population of which was eliminated by a single cat belonging to the island's lighthouse keeper (Oliver, 1955). Likewise, the Socorro dove Zenaida graysoni has also been driven to extinction primarily by cats (Jehl & Parks, 1983). Similarly, mammalian species such as hutias Geocapromys spp. ...
1. A questionnaire survey of the numbers of animals brought home by domestic cats Felis catus was conducted between 1 April and 31 August 1997. A total of 14 370 prey items were brought home by 986 cats living in 618 households. Mammals made up 69% of the items, birds 24%, amphibians 4%, reptiles 1%, fish < 1%, invertebrates 1% and unidentified items 1%. A minimum of 44 species of wild bird, 20 species of wild mammal, four species of reptile and three species of amphibian were recorded.
2. Of a sample of 696 individual cats, 634 (91%) brought home at least one item and the back-transformed mean number of items brought home was 11.3 (95% CI 10.4–12.2). The back-transformed means and number of cats retrieving at least one item from each prey group were: 8.1 (7.4–8.9) mammals for 547 (79%) cats, 4.1 (3.8–4.5) birds for 506 (73%) cats, 2.6 (2.2–3.0) herpetofauna for 145 (21%) cats and 2.2 (1.8–2.7) other items for 98 (14%) cats.
3. The number of birds and herpetofauna brought home per cat was significantly lower in households that provided food for birds. The number of bird species brought home was greater in households providing bird food. The number of birds and herpetofauna brought home per cat was negatively related to the age and condition of the cat. The number of mammals brought home per cat was significantly lower when cats were equipped with bells and when they were kept indoors at night. The number of herpetofauna brought home was significantly greater when cats were kept in at night.
4. Based on the proportion of cats bringing home at least one prey item and the back-transformed means, a British population of approximately 9 million cats was estimated to have brought home in the order of 92 (85–100) million prey items in the period of this survey, including 57 (52–63) million mammals, 27 (25–29) million birds and 5 (4–6) million reptiles and amphibians.
5. An experimental approach should be taken to investigate the factors found by this descriptive survey to influence the numbers of prey brought home by cats. In particular, investigation of potential management practices that could reduce the numbers of wild animals killed and brought home by cats will be useful for wildlife conservation, particularly in suburban areas.
... Originally described in the genus Harporhynchus (0Toxostoma ), its systematic position has long been the subject of debate or neglect. Its anatomical structure suggested to some that Mimodes is a relict form of an ancestral link between mockingbirds and thrashers (Jehl and Parkes 1983). Externally, Mimodes resembles a thrasher, with upperparts plain brown, underparts dull brownish, and wings and tail without white. ...
Recently acquired tissue makes possible a first molecular assessment of the taxonomic position of the Soccoro Island endemic mimid Mimodes graysoni. Mitochondrial DNA sequence data from the ND-2 gene was analyzed using parsimony, maximum likelihood and bayesian methods of inference. These methods all placed Mimodes graysoni within a strongly supported clade containing four representatives of the genus Mimus. Retention of the monotypic Mimodes would make Mimus paraphyletic, therefore Mimodes graysoni is more properly placed in the genus Mimus.
... A combination of factors such as the lack of antipredator behaviour of island preys and the catholic diet of feral cats has had a devastating effect. This opportunistic predator (Fitzgerald, 1988) has been directly responsible for numerous island extinctions of mammals (Mellink, 1992;Tershy et al., 2002), reptiles (Iverson, 1978;Mitchell et al., 2002) and birds (Jehl & Parks, 1983;Lever, 1994;Veitch, 2001) worldwide. Due to the dramatic effects caused in island biotas, intensive eradication campaigns have been successfully carried out in at least 48 islands worldwide (Nogales et al., 2004). ...
The ecological effects and distribution of 13 invasive non‐native mammal species on the Canary Islands are reviewed.
Six species, representing six different taxonomic orders, are widely distributed and live on all seven main islands of the Canarian Archipelago: Felis catus , Capra hircus , Rattus rattus , Rattus norvegicus , Mus domesticus and Oryctolagus cuniculus . Atelerix algirus is found on four islands while six further species are present on only one island: Crocidura russula , Suncus etruscus , Rousettus egyptiacus , Ovis gmelini , Ammotragus lervia and Atlantoxerus getulus .
Five species have an omnivorous diet, four are herbivorous, two insectivorous, one frugivorous and one carnivorous. The ecological effects and damage caused by these species in the natural habitats of the Canaries are similar to those in other insular regions. To our knowledge, the effects of two species, A. lervia (herbivorous) and A. getulus (omnivorous), are as yet unreported for other insular environments.
Two of the most pernicious effects caused by invasive non‐native mammal species in the Canaries consist of predation by feral cats of the three giant lizard species present in the western islands, but especially Gallotia gomerana , which is now on the verge of extinction; and the damage that the four species of herbivores cause to the endemic flora of the archipelago.
This paper assesses the legacy of isolation from the mainland and the influence of other factors on biodiversity,
biogeography, and faunal and floral change on islands of Western Australia (WA). An empirical perspective
from WA reveals numerous neglected insights and overlooked factual information, illustrating the need for
improved synthesis of existing knowledge in order to understand the generality of biodiversity patterns and
change on islands. A recent loss of direction in the discipline of island biogeography appears to have resulted
from over-emphasis of island area, distance from mainland, and absence of competitor species as the key variables
in explaining the nature and evolution of insular biodiversity. While these three factors are relevant, they are not
always sufficient and should instead be considered as embedded in a more general set of 12 parameters, namely
geographic location (including climatic conditions and geomorphological features); history (both geological and
human); productivity (soil nutrient status); disturbance (including degree of exposure to salt-laden winds and
the presence of Indigenous people); occurrence of breeding marine birds and mammals (particularly significant
on small islands); and sampling compatibility. These nine factors are less unequal than is conceded in the literature.
Furthermore, most of the 12 factors are interconnected and interdependent, and in combination provide a more
satisfactory explanation of insular phenomena. However, the relative influence of these factors differs among
species and among higher taxa.
Baselines for the biotas of WA islands date from 1843 (for landbirds and seabirds), much earlier than for mammals
(1906), plants (1950), and butterflies (1969). Most WA islands demonstrate no extinctions or immigrations of
landbird species, evidence of a static equilibrium. On some other WA islands, immigrations of native landbird
species exceed extinctions. Immigrations of seabird species also exceed extinctions. In contrast, the native mammal
fauna of WA islands shows few immigrations or extinctions unrelated to human activities. The floras of WA
islands show numerous immigrations of species, many of which involve plant species not native to WA. Island
floras generally exhibit many extinctions and immigrations, with small islets having the most stable floras.
Before Europeans settled WA, it appears that species turnover on islands was either non-existent or infrequent.
The concept of punctuated equilibrium appears to provide a better explanation of ongoing biodiversity change
on islands than dynamic equilibrium, with the intrusion of humans representing a turning point. Dynamic
equilibrium is then a special case applicable to relatively short time scales and islands within the dispersal
capabilities of species in a particular taxon.
We are optimistic about the future of biodiversity on the islands of WA if current policies, management and
monitoring are maintained and strengthened. Garden and Barrow islands, with their extensive naval or mining
infrastructure, demonstrate successful coexistence for at least several decades between humans and biodiversity.
The main challenge to protecting biodiversity on the islands of WA is to prevent the establishment of pest species,
particularly of ants, rodents, cats (Felis catus), house mice (Mus musculus) and weeds, and plant and animal
diseases. Continual and vigilant monitoring and public education are required. To facilitate this, we recommend
that one management plan be prepared to apply to all islands of WA.
Our review concludes with numerous suggestions for future research on the islands of WA, as well as on
continental and oceanic islands globally. We advocate a systematic comparative approach, based on a
comprehensive global synthesis of information already available on islands in the ecological and natural history
literature. Fifteen themes are briefly outlined. Regional syntheses will remain important, but many more are
needed in order to achieve effective global synthesis and a more complete and holistic understanding of island
ecology. These suggestions should result in improved knowledge about insular biodiversity and more
comprehensive protection and management of island life.
Actualmente, en el país residen al menos 46 de las 100 especies
invasoras más dañinas del mundo y están afectando los
ecosistemas en todo el territorio nacional. Solo la suma de
plantas vasculares y vertebrados invasores registrados en México
es de 724 especies. Esta cifra sin duda es una subestimación
debido a que los esfuerzos dirigidos a enfrentar este problema
atienden solo las actividades productivas y no los ecosistemas
naturales. En este capítulo se presenta una evaluación del estado
actual de la invasión de especies exóticas; se ofrece un marco
conceptual general, junto con definiciones básicas, y se hace una
breve revisión histórica de los patrones de introducción de las
mismas. En particular se analizan las principales consecuencias de
la flora y la fauna introducidas en los ecosistemas mexicanos,
enlistando varias de las especies más peligrosas presentes en el
país. Después se describen las técnicas disponibles para su
control y erradicación, y se revisan algunos casos en el país, junto
con el análisis del marco legal relacionado con la prevención,
manejo y control de las especies invasoras. Finalmente, se
analizan las lecciones aprendidas y se señalan las necesidades de
investigación, de vinculación y con respecto a las estrategias
apropiadas en los ámbitos regional y nacional.
Socorro Island, the largest and biologically most diverse of the four islands of the Revillagigedo Archipelago (Brattstrom 1990), confronts serious problems related to human activities. Eight endemic taxa of land birds now breed on Socorro: Yellow-crowned Night Heron, Nyctanassa violacea gravirostris; Socorro Red-tailed Hawk, Buteo jamaicensis socorronensis; Socorro Ground Dove, Columbina passerina socorroensis; Green Parakeet, Aratinga holochlora brevipes; Socorro Wren, Thryomanes sissonii; Socorro Mockingbird, Miraodes graysoni; Tropical Parula Warbler, Parula pitiayumi graysoni; and Socorro Towhee, Pipilo erythrophtalmus socorroensis (McLellan 1926, Jehl and Parkes 1982, Brattstrom 1990). Jehl and Parkes (1983) have proposed that domestic cats (Fells catus), introduced since 1957, are responsible for the extirpation of the endemic Socorro Dove, Zenaida graysoni, and reductions of other species, especially the Socorro Mockingbird. However, no quantitative data on predation by feral cats on Socorro Island have been previously reported in the literature. We present here an analysis of the diet of feral cats on Socorro Island. Socorro Island, located approximately 450 km south of the tip of the peninsula of Baja California, covers about 14,000 hectares (16 x 11 km). This island is a volcanic cone whose highest point is Mount Evermann (1050 m). Climate is arid tropical with an average annual temperature of 24.8 ø C and average annual precipitation of 327.7 mm. Fresh water is found in the puddles formed after tropical storms and continuously in several caves. From 16 to 28 February and from 7 to 12 May 1990 we conducted our field research on Socorro Island, intensively searching for scats, tracks, and other indirect evidence of feral cats, specially in the south portion of the island. We searched in Croton scrub (40 m elevation), disturbed grassland, and forest (650 m elevation). Presumably, the scats we found were from different individuals, as they were widely dispersed. We found and analyzed 31 scats, comparing the remains of scales, bones, feathers, and hairs with those of the collection of Centro de Investigaciones Bio16gicas. Table 1 shows the occurrence of items in 31 scats found during February and May 1990. Feral cats were feeding mainly on House Mice (Mus musculus), endemic lizards (Urosaurus a u riculatus), some birds, and also crabs, insects, scorpions, and various vegetable materials (Table 1). Birds were present in 22.6% of the cat scats (February and May samples combined). The Socorro Ground Dove and Tropical Parula Warbler were the two bird species found most often in the scats, five and three times, respectively. A recent colonizer, the Mourning Dove (Zenaida macroura), was present in two of the 31 analyzed scats. Although we did not find remains of another recent colonizer, the Northern Mockingbird (Mimus polyglottus), in May we found feathers of one in the field, presumably eaten by a feral cat. Jehl and Parkes (1982) reported predation by cats on Townsend's Shearwater (Puffinus auricularis), but we did not find evidence of this perhaps because our searches were not made near the shearwater colonies. Our results suggest that predation on birds by feral cats is not very important. However, even limited predation may seriously affect a species as endangered as the Socorro Mockingbird. This species' population may be approximately 60-70 pairs (Castellanos and Rodriguez-Estrella 1990, L. Baptista pers. comm.), and we found evidence that it is preyed upon by Socorro Red-tailed Hawks (a Socorro Mockingbird
Food webs on oceanic islands are often markedly different from continental food webs due to low species diversity and absence of key components of mainland ecosystems. Food webs and feeding habits are described from observations and scat, pellet, and gut analysis on the four islands of the Revillagigedo Islands, Mexico, when in their near-original state. Changes in food habits after introduction of exotics are described. Food webs increase in complexity with increase in island size, largely as a function of increase in habitat diversity seen with an increase in island size. Seabirds are the major components of food webs on the two smaller islands, and reptiles, passerine birds, hawks, owls, parrots, and doves are more important on the two larger islands. Some island vertebrates have food habits similar to those of their mainland counterparts, but others have become food specialists (e.g., the Socorro Red-tailed Hawk, in the absence of small mammals, eats mostly lizards and land crabs). Other birds have seasonally or permanently switched food (ravens and owls on Clarión eat cactus, towhees eat insects, red-tailed hawks eat plants). Some of this food switching may be due to presence of a harsh dry season and/or to the unique fauna and flora of the islands. Insectivorous birds on Socorro apparently reduce competition by utilizing different foraging heights, habitats, and feeding methods. Sheep introduced onto Socorro in 1869, whose numbers fluctuated over the years, destroyed some vegetation, but they have now been eradicated. Exotics introduced in connection with military garrisons and an airfield may have major effects on the ecosystem of these islands in the future.
Reviews the status of the birdlife through 1982, provides an historical review of research, and provide a bibliography. -from Authors
Long-term ecological studies are desirable, but rare. I here present data from a 60-year study on the repopulation of San Benedicto Island following a volcano eruption in 1952. Bárcena Volcano appeared on 1 August 1952 on San Benedicto Island, Revillagigedo Islands, Mexico. Within 20 min, the entire island was engulfed in a cloud of ash and pumice, which covered all the plants, killed an estimated 20 000 sea birds within hours and caused the subsequent extinction of an endemic race of rock wren (Salpinctes obsoleta exsul). The results of studies on revegetation and repopulation of the island for the first 10 years after the volcanic eruption were summarised by Brattstrom in 1963. This report extends the studies to 2012. The distribution of the land crab (Aegecarcinus planatus) has increased on the island. By 1971 the crab occurred only over the northern one-eighth of the island, but by 1978 it could be found on one-third of the island. No studies on its distribution have been made since then. Total sea bird populations steadily increased up to 1971 and then rapidly declined, though these changes in numbers are largely due to a fluctuation in the populations of the masked booby (Sula dactylatra). The changes in the booby population may have been due to reproductive and feeding success or to immigration and emigration. The decline in the shearwater (Puffinus ssp.) populations are largely due to erosion and destruction of their burrows; their numbers did not increase until 2000. The formation of a large lava delta created a new habitat, which permitted the establishment of a species of sea bird new to the island, the red-footed booby (Sula sula). Numerous non-resident waifs or stray birds have been observed on the island but most have not become established. The exception is the Laysan albatross (Phoebastria immutabilis), breeding at present in low (3–712) numbers. The original flora consisted of 10 species. The volcano caused four species to become extinct, two re-established themselves, and two species new to the island arrived. There have been marked erosional changes, and the accidental introduction of exotic plants may dramatically alter the vegetation of the island.
This article reviews the biology, ecological effects, and management of the domestic cat (Felis catus) in the Pacific basin. The cat is one of the most controversial invasive species in the Pacific region because of its complex relations with humans. At one extreme, well-fed domestic house pets are allowed outdoors where they may hunt native animals; at the other, unsocialized feral cats have replaced native predators as apex predators or occupy a new niche on oceanic islands, where they have devastated native faunas. In the middle are stray cats that are still socialized around humans. Feral and stray cats can be reservoirs of diseases that infect free-roaming domestic cats, humans, and wildlife. Given these problems, the best response would be to keep domestic cats indoors, restrict cat breeding, and remove feral populations. However, most Pacific basin societies have failed to reach a consensus on the cat problem, so solutions are ad hoc, often lacking in any scientific basis, and reflect our conflicting views. Compromise management might best fall into three broad classes: (1) eradication of cats should be confined to islands and other areas of high native biodiversity where reintroduction can be prevented; (2) in a landscape of low or moderate biological value, efforts should be made to educate the public to reduce the impact of their cats on remaining wildlife, while excluding cats from “islands” of elevated biodiversity values or human sensitivity; (3) in drastically simplified urban ecosystems, management perhaps should occur only in response to local complaints.
Following an isolation gradient in West-Mexico the avifauna of three study areas is investigated, on mainland reserve and two island groups. The avifaunas are described and analysed regarding species richness, environmental attributes, ende-mism, broader ecological niches, and brood status. The taxonomical composition is determined on different hierarchy levels. Most species records come from mainland Chamela (262), followed by the coastal Marias (191) and the oceanic Revilla-gigedos (148). Thereof 139 bird species breed in Chamela, 61 on Marias and only 29 on the Revillagigedos. In total, in the three study areas 364 species were recorded, which belong to 22 orders. On island groups generally less taxa per hierarchy level are present than on the mainland, especially on the remote Revillagigedos. Here, on average 1.7 species are found per genus, 2.2 genera per family, and 2.5 families per order. In the analysis of the taxonomical hierarchy relations to each other an isolation gradient is identified: from mainland Chamela via the coastal Marias to the oceanic Revillagigedos the degree of relatedness decreases on average. The results support the theoretical hypothesis that on islands closely related taxa tend to exclude each other and that one generalist tends to replace several specialists. Small ecological niches are often not occupied by specialist species on islands, but are used by generalists.
Feral cats (Felis catus) introduced to new environments have caused the extinction of many vertebrate species,
including six species of birds on Guadalupe Island, México. To save species from extinction and restore natural processes, cats have been eradicated from islands using a variety of techniques. Eradication campaigns have to be planned carefully; ideally supported by information about the population to be eradicated. Our study focuses on home range estimation (fixed kernel); bait consumption by feral cats and non-target species; and diet of feral cats on Guadalupe Island. Home range was 76 to 1098 ha (KE 95) and core areas 21 to 196 ha (KE 50). Feral cats and non-target species including Guadalupe junco (Junco hyemalis insularis), Guadalupe rock wren (Salpinctes obsoletus guadalupensis), western gull (Larus occidentalis), and house mouse (Mus musculus) consumed baits. Items most commonly found in diet samples were mice (66.5%) and birds (16.8%). Male cats were 2.9 ± 0.6 kg, and females 2.4 ± 0.9 kg. The results of this study will inform eradication decisions for Guadalupe Island, especially regarding the use of poison baits.
Keywords: Morphometrics, Mus musculus, Junco hyemalis insularis, Salpinctes obsoletus guadalupensis, Larus
occidentalis, non-target species, birds, poison baits.
On Mexican islands, 20 island endemic species and subspecies of vertebrates have gone extinct in the last 100
years; all but four of these extinctions were caused by invasive mammals. To prevent more extinctions, 49 populations of 12 invasive mammals were eradicated from 30 Mexican islands. These actions protected 202 endemic taxa – 22 mammals, 31 reptiles, 32 birds, and 117 plants – as well as 227 seabird breeding colonies. An area of 50,744 ha was restored, which represents 10% of Mexico’s total island territories. Techniques have ranged from the traditional – trapping and ground hunting – for 26% of the restored area, to the most sophisticated – aerial hunting, aerial broadcast of bait, DGPS and GIS use – for 74% of the restored area. These conservation actions are of high signifi cance for Mexico. Extirpated seabirds have recolonised several islands and increased reproductive success has been documented. An ongoing seabird social attraction project facilitates recolonisation of additional islands. On Guadalupe Island, after the eradication of goats
(Capra hircus), recruitment of three endemic trees increased from zero to more than 150,000 individuals. Six native plants, including two endemics, were rediscovered. Ecological outcomes from island restoration are expected to increase. Eradicating all invasive vertebrates from the remaining 41 Mexican islands with 83 populations of invasive mammals is a viable and strategic goal, achievable by 2025, and will set a global benchmark.
Keywords: Eradication, restoration, invasive mammals, islands, Mexico, ecological outcomes, strategic goal.
The avifauna of three oceanic islands of the Revillagigedo archipelago in the eastern Pacific Ocean consists of 14 endemic landbird taxa and 3 recent continental colonists. This study analyzes the origin, areography of continental relatives, ecological characteristics, and role of immigration and extinction factors as regulators of the islands' species. Only two natural extinctions have been detected on this archipelago in more than 130 years. The endemic nature of the pristine avifauna is interpreted as an indication of high stability over thousands of years. The MacArthur–Wilson (1967) “equilibrium theory of island biogeography” cannot explain or predict the persistence of this avifauna adapted to stable and unique island ecosystems. Lack's (1976) “theory of ecological poverty” regulating island avifaunas, however, predicts stability and a resource-limited bird community. The Revillagigedo avifauna can be understood as an interactive community of a few highly adapted and competitive ecological generalists that have effectively filled all niche spaces and closed off the islands to further colonization. Catastrophic change or anthropogenic landscape degradation may, however, create novel niche spaces and open affected islands to new colonists. This appraisal lends support to the call for a shift away from application of the equilibrium model of island biogeography in conservation science. [Key words: island biogeography, equilibrium theory, island stability, island avifauna, MacArthur-Wilson, Lack, Revillagigedo Islands, Socorro Island.]
This chapter investigates the direct impacts of introduced seabird predators on the terrestrial plants and other animals that inhabit seabird islands. It discusses the direct effects of seabird predators on arthropods, mollusks, amphibians, reptiles, land birds, mammals, and plants. It analyzes various studies that look into what determines species' vulnerability to seabird predators. It contains information gathered from systems where the predators are not native. It focuses on five species: cats, foxes, pigs, rats, and mice and looks into their effects on the island's ecology. It also considers the inherent limitations that pose difficulties in assessing the impacts of introduced predators.
Isla Beata and Isla Alto Velo are small satellites of the Dominican Republic, lying off its southwestern coast. We visited Isla Beata between 26–30 July 1977 and 20–21 October 1978. We explored Isla Alto Velo on 22 October 1978. In addition we made aerial surveys of the islands in 1977 and 1980. In our surveys we found 34 species, including 16 land birds, not before reported for Isla Beata. The Hispaniolan Parakeet (Aratinga chloroptera) and Hispaniolan Woodpecker (Mélanerpes striatus) are reported for the first time from offshore islands. This brings the number of reported species for Isla Beata to 93, with 44 land birds. We found 22 species on Isla Alto Velo, for a total of 27 species, including 12 land birds, for the island.
While food supply and other resources provide the ultimate check on bird numbers, some populations might be held by predators below the level that resources would permit (Lack, 1954; Newton, 1980; Martin, 1991). Although practically all birds are subject to predation, at least at the egg and chick stages, it is extremely difficult to assess the effects of this predation on population levels. Even where predators kill a large proportion of their prey each year, they do not necessarily reduce breeding numbers. The numbers of many bird species can more than double each year through breeding so that, if they are to remain stable from year to year, more than half the individuals present at the end of one breeding season must die before the next, if not from predation then from something else. For predators to reduce a breeding population below the level that would otherwise occur, at least part of the mortality they inflict must be “additive” to other mortality, and not simply “compensatory,” replacing other forms of death.
We recorded 62 bird species on Clarion Island, Mexico (Revillagigedo Archipelago, Pacific Ocean) during 1998–2006, eight of which breed there, 52 are considered non-breeders, and breeding is likely but unconfirmed for the Red-billed Tropicbird (Phaethon aethereus), Nazca Booby (Sula granti), and an unidentified shearwater. Thirty species are new for the island. A census of the Clarion Burrowing Owl (Athene cunicularia rostrata) in 2002/03 suggested a maximum total population of 850 pairs. At least 46 pairs of Laysan Albatrosses (Phoebastria immutabilis) bred in 2002/03, but the species experienced total breeding failure during our study. This result was unexpected because feral pigs (Sus scrofa) were successfully eradicated from Clarion by 2002; endemic Clarion Ravens (Corvus corax clarionensis), an endemic snake (Clarion Racer, Masticophis anthonyi), and an unidentified ant were associated with egg and hatchling failures. A small colony of an unidentified shearwater could be a recolonization by the endemic and Critically Endangered Townsend's Shearwater (Puffinus auricularis) or Wedge-tailed Shearwater (P. pacificus), which has not been recorded for Clarion Island.
Abstract The Socorro dove Zenaida graysoni, endemic to Socorro Island, was last reported in the wild in 1972. Fortunately, the species has been propagated in zoos in Europe and the USA, and plans are underway to reintroduce it to its native habitat. This will be the first known attempt to return a bird species extinct in the wild to its ancestral island. In order to assess the disease threats the Socorro dove may face, the avifauna of Socorro Island, with a specific focus on Socorro ground doves Columbina passerina socorrensis and mourning doves Zenaida macroura, as well as Socorro doves in captivity, were screened for blood parasites of the genera Plasmodium, Haemoproteus, Leucocytozoon and Trypanosoma spp. We found Haemoproteus spp. in 17 (74%) of 23 Socorro ground doves, 23 (92%) of 25 mourning doves and 3 (14%) of 21 northern mockingbirds, all other bird species did not show infections. Here we report the phylogenetic analysis of 19 distinct lineages of Haemoproteus spp. detected in birds of Socorro Island and compare their evolutionary relationships to parasites detected in the avifauna of the Galápagos Islands, continental Latin America and Europe. Microscopic examination revealed one mourning dove infected with Plasmodium (Haemamoeba): thus underscoring the importance of using both PCR and microscopy when analyzing bird blood samples for hemosporidian parasites. This study confirms that the Socorro dove will most likely be exposed to Haemoproteus spp. that currently infect mourning doves and Socorro ground doves of Socorro Island. A monitoring program for both birds and vectors should be implemented to establish the prevalence of Plasmodium, and as a necessary conservation measure of critically endangered birds on the island.
The Socorro Mockingbird Mimodes graysoni is endemic to Socorro Island, Mexico, and has declined dramatically in this century. Study of its population size, distribution, and structure is currently under way to help assess its conservation status. In 1993 and 1994 215 Socorro Mockingbirds were ringed; a modified Lincoln index yielded a population estimate of 353 ± 66 individuals in 1994. Most of the birds observed occupied a small region at high elevation that covered less than 10% of the island's area. Average territory size was 1.48 ± 0.71 ha, n = 11. Of the 86 birds banded in 1993 67% were adults and 33% subadults. Of the 170 birds detected in 1994, including new captures and ringed individuals from the previous year, 44% were adults and 56% subadults. In 1993 62% were male and 38% female; in 1994 56% were male and 44% were female. The sex ratio of the population was similar to that of other undisturbed Mimid populations, which argues against the possibility that cats might prey disproportionately on incubating females. Moreover, the presence of young birds in both years indicates that successful reproduction was occurring and that the population was not suffering catastrophic nest failure, as might be caused by cat predation on nestlings or fledglings. Northern Mockingbirds Mimus polyglottos, which first arrived on Socorro in the 1970s, occupied mainly open areas produced by sheep grazing, which suggests that the Socorro Mockingbird is not being competitively displaced. Our observations indicate that habitat degradation by sheep is the most probable cause of the Socorro Mockingbird's decline.
The paper examines the role of feral sheep (Ovis aries) in facilitating the naturalization of alien plants and degrading a formerly robust and stable ecosystem of Socorro, an isolated oceanic island in the Mexican Pacific Ocean. Approximately half of the island is still sheep-free. The other half has been widely overgrazed and transformed into savannah and prairie-like open habitats that exhibit sheet and gully erosion and are covered by a mix of native and alien invasive vegetation today. Vegetation transects in this moderately sheep-impacted sector show that a significant number of native and endemic herb and shrub species exhibit sympatric distribution patterns with introduced plants. Only one alien plant species has been recorded from any undisturbed and sheep-free island sector so far.
Socorro Island provides support for the hypothesis that disturbance of a pristine ecosystem is generally required for the colonization and naturalization of alien plants. Sheep are also indirectly responsible for the self-invasion of mainland bird species into novel island habitats and for the decline and range contraction of several endemic bird species.
The population size of the Socorro Mockingbird Mimodes graysoni, which represents a monotypic genus endemic to Socorro Island, México, has declined dramatically within the last 40 years. Postulated causal factors include competitive exclusion by Northern Mockingbirds Mimus polyglottos, predation by feral cats and overgrazing by feral sheep. Habitat degradation looms as the primary candidate because surviving Socorro Mockingbirds live mainly in areas of the island with little apparent habitat damage, and because Northern Mockingbirds and cats both arrived on Socorro after much of the decline had occurred. Isolating key factors is difficult, however, because the present distributions of cats and Northern Mockingbirds coincide broadly with patterns of habitat degradation. To investigate habitat requirements of the endemic mockingbird in detail, we measured vegetation characteristics at localities with and without Socorro Mockingbirds, and observed their foraging behaviour. Socorro Mockingbirds occupied sites in montane regions covered with Ilex socorroensis, Guettarda insularis, Triumfetta socorrensis and Eupatorium pacificum; they were also abundant in pristine lowland forests. Socorro Mockingbirds were scarce in disturbed forests where Dodonaea viscosa has replaced the original understorey, and they were absent from low-elevation Croton masonii scrub, even in areas with no signs of degradation. Restoration of degraded habitat could help the population of Socorro Mockingbirds grow and reoccupy more of its former range.
Many bird species were extirpated or became extinct when prehistoric man reached oceanic islands We list > 200 species of extinct island birds only recorded as sub-fossils and which probably vanished due to prehistoric man In addition we list c 160 cases where an extant species has been found as subfossil on islands where it no longer occurs Several species today considered endemic to single islands of island groups had a much wider distribution in the past Biogeographic analyses of insular avifaunas are almost meaningless it the extensive prehistoric extinctions are not taken into account
Most extinct species belong to Anatidae Rallidae and Drcpanididae while local extirpations are numerous among doves and seabirds Smaller birds are rare mainly due to sampling bias and taphonomic factors The bird populations were depleted mainly by overhunting predation by introduced vertebrates and alteration of the original vegetation
Prehistoric humans on islands although dependent on limited animal resources regularly failed to exploit these in a sustainable way Several cases where human populations disappeared from islands in the Pacific may have been due to over-exploitation of native animals
Prehistoric man reached most tropical and temperate islands and most of the few remaining island faunas have been severely depleted in historic times The prehistoric extinctions emphasize the extreme vulnerability and value of the very few pristine island faunas that still remain
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