Rodent carcasses are a source of food and a biological hazard that can commonly be found in natural and anthropic ecosystems. Therefore, this article aims to determine which organisms consume those ...carcasses in an urban reserve. For this, 53 rodent carcasses were placed in front of camera traps to record their consumers. The final destiny of 41 carcasses is known: 76 % were consumed by opossums (
) and 24 % by ringtails (
). Flies and ants attempted to take advantage of the carcasses but in all cases ended up losing the competition to mammals. Opossums are the most efficient carrion consumers, as they exhibit learning as to where the carcasses are located and are able to consume old carcasses (up to 10 days old). This suggests that mid-size mammals, especially opossums, are providing an important ecological and health service for both natural ecosystems and human populations by removing rodent carcasses that otherwise could become sources of infection.
The choice of methods for trapping animals can greatly affect the studies and their results, despite that there are relatively few studies on the matter. Thus, the purpose of this study is to compare ...two common methods of live trapping (Tomahawk traps and pitfall traps), their efficiency and ethical implications for trapping Virginia opossums (Didelphis virginiana). Traps were located in a paired design, the trapped animals were checked for sex, injuries caused by the trap and stress level, then marked and released in the same spot. At the same time, costs of both trap types were compared. Tomahawk traps were 60 % more efficient to trap opossums but the pitfall traps had better results in all the other categories: were more cost-effective, did not injure the animals as often and were less stressful. Neither type of trap presented bias in sex proportion or number of recaptured animals. In general, both types of traps resulted to be effective, the pitfall trap was the better option in almost all of the categories but has the disadvantage that in the infrequent event of two males being caught on in the same trap, they are likely to fight.
La elección del método de trampeo de los animales puede afectar de manera considerable los resultados de los estudios, a pesar de esto hay pocos estudios de este tema. Por lo tanto, el objetivo de ...este trabajo es comparar dos métodos comunes para capturar animales vivos (trampas Tomahawk y trampas de caída), y su eficiencia e implicaciones éticas para atrapar tlacuaches norteños (Didelphis virginiana). Las trampas se colocaron en un diseño pareado; a los animales se les tomaron los datos de sexo, heridas causadas por la trampa y nivel de estrés, posteriormente se marcaron y se liberaron en el sitio de captura. También se compararon los costos de ambos tipos de trampa. Las trampas Tomahawk resultaron 60 % más eficientes, pero las trampas de caída tuvieron mejores resultados en todos los demás aspectos: tuvieron mejor costoeficiencia, rara vez causaban heridas a los animales y estos estaban menos estresados. Ningún tipo de trampa presentó sesgos en la proporción sexual ni el número de animales recapturados. De manera general, ambos tipos de trampa resultaron eficientes, la trampa de caída fue la mejor en la mayoría de los aspectos, pero su desventaja consiste en que en el poco frecuente caso de que dos machos sean capturados en la misma trampa, es muy posible que se peleen. Palabras clave: costo-eficiencia; Didelphis virginiana; México; REPSA; métodos de trampeo The choice of methods for trapping animals can greatly affect the studies and their results, despite that there are relatively few studies on the matter. Thus, the purpose of this study is to compare two common methods of live trapping (Tomahawk traps and pitfall traps), their efficiency and ethical implications for trapping Virginia opossums (Didelphis virginiana). Traps were located in a paired design, the trapped animals were checked for sex, injuries caused by the trap and stress level, then marked and released in the same spot. At the same time, costs of both trap types were compared. Tomahawk traps were 60 % more efficient to trap opossums but the pitfall traps had better results in all the other categories: were more cost-effective, did not injure the animals as often and were less stressful. Neither type of trap presented bias in sex proportion or number of recaptured animals. In general, both types of traps resulted to be effective, the pitfall trap was the better option in almost all of the categories but has the disadvantage that in the infrequent event of two males being caught on in the same trap, they are likely to fight. Key words: cost-efficiency; Didelphis virginiana; Mexico; REPSA; trapping methods
Human food waste is an essential resource for many animals that inhabit urban ecosystems and has allowed some species to proliferate in cities. Virginia Opossums (
Didelphis virginiana
) are ...considered a good example of this process; however, the real role of waste in this animal’s diet is still unclear. Therefore, this study aims to compare opossums’ diet from urban and natural areas in Mexico City. Opossums were live-trapped, and samples of hair and blood were taken to perform a stable isotope analysis of C and N. The results show that opossums from natural and urban areas, in general, have a very similar isotopic niche; however, one natural location fell out of this pattern, and here opossums based their diet on C3 plants. This suggests that opossum diets have a similar carbon source and occupy a similar trophic position in urban and natural areas. However, there is a separation between opossums in urban and natural areas, not so much in the isotopic niche, but in the feeding habits since natural areas, opossums prefer to feed in their distribution area despite the availability of better quality food in the nearby urban areas.
Resumen La reproducción requiere grandes cantidades de energía, por lo que muchos organismos buscan las temporadas idóneas para realizarla. Por ejemplo, se espera que cada población del conejo ...castellano, Sylvilagus floridanus, ajuste su ciclo de vida para reproducirse en la temporada del año más adecuada, la cual puede variar dependiendo de las condiciones del sitio donde cada una vive. El objetivo de este estudio fue conocer en qué momento del año se reproduce esta especie de conejo en el matorral xerófilo del Pedregal de San Ángel, Ciudad de México, con base en un análisis de variación estacional de la abundancia y tamaño de sus excretas. Se hicieron muestreos mensuales de abundancia de heces en sitios establecidos por 4 años, y durante el primer año, también se registró el tamaño de las excretas. Se analizaron los datos usando una prueba de χ2. Se registró que las pastillas fecales pequeñas se concentran en septiembre y que los mayores valores de abundancia se registraron entre octubre y diciembre. Los datos sugieren que el periodo reproductivo sucede en agosto, que es un mes de mayor disponibilidad de alimento. Los datos obtenidos no coinciden con la temporada reproductiva que registra esta especie en otras localidades.
Abstract
Urban animals can be an important threat to human health as possible hosts of zoonotic diseases and their susceptibility to these diseases can depend on their overall health conditions. ...Thus, it is important to understand the factors that determine their health conditions. For this, we studied Virginia opossums (Didelphis virginiana) in six locations with different urbanization levels and types in Mexico City, Mexico. We trapped opossums and measured eight health-related characteristics (number of ectoparasites and tartar severity, among others) and estimated the percentage of area covered by the four main types of terrain (natural vegetation, managed vegetation, impermeable terrain and constructions). Data were analyzed by a canonical correspondence analysis. We found that impermeable terrain was related to negative health characteristics, while the constructions were opposite to impermeable terrain and mostly related to good health characteristics. At the same, time constructed areas held a smaller population than the natural areas. This suggests that constructed areas provide few shelters, but opossums are healthier there, while impermeable areas provide more shelter but cause more health problems to the animals, thus increasing the chances of zoonotic diseases. We recommend reducing the impermeable areas in city planning to contribute to a better health of the urban animals and therefore reduce risks of zoonotic diseases with potentially disastrous results.
We studied factors that affect the abundance of feces of the eastern cottontail (Sylvilagusfloridanus) in an ecological reserve in Mexico City. We measured the abundance of fecal pellets as an ...estimator of cottontail abundance, as well as different factors that may affect their abundance: predator presence, terrain ruggedness, soil depth, and plant cover. We found that predator presence was the most important factor reducing the abundance of cottontails, whereas terrain ruggedness was the second most important because the cottontail cannot climb effectively. Plants were less significant than expected but Manfreda scabra had a substantial positive effect on cottontail abundance.
A pesar de su abundancia y el importante papel que juegan en los ecosistemas, la dieta del conejo serrano, Sylvilagus cunicularius, no se ha estudiado lo suficiente. Los estudios previos solamente ...reportan el consumo de especies de la familia Poaceae por parte de este conejo. En esta nota reportamos el consumo de Eryngium proteiflorum por el conejo serrano en el Pico del Águila, localizado en la cima del volcán Ajusco, Ciudad de México, México. Los conejos comen las hojas de E. proteiflorum empezando por la base para evitar sus espinas y usan este recurso durante todo el año. Por lo tanto, E. proteiflorum podría ser una importante fuente de nutrientes para los conejos y éstos parecen ser importantes consumidores de la planta.
La depredación de ardillones de roca (Otospermophilus variegatus) por serpientes de cascabel (Crotalus sp.) ha llevado a un proceso coevolutivo durante el cual los ardillones han desarrollado ...resistencia al veneno de serpiente de cascabel y una serie de comportamientos complejos que les permiten protegerse contra la depredación. En esta nota describimos una observación de tal comportamiento; cómo una madre ardillón protege a un joven contra el ataque de una serpiente de cascabel. Fuimos testigos de un enfrentamiento entre una madre ardillón y una serpiente de cascabel por un juvenil que fue atacado por la serpiente, y la estrategia utilizada para guiar a su cría lejos del peligro. La madre ardillón amenazó a la serpiente de cascabel moviendo su cola y se retiró lateralmente a un árbol cercano. El juvenil siguió a la madre guiado por su olor. Cuando llegaron a una distancia segura, saltaron del árbol y se alejaron manteniendo la distancia. Antes de retirarse, la madre intentó interactuar con los observadores. Trabajadores locales confirman que las ardillas les advierten sobre la presencia de serpientes de cascabel. El comportamiento defensivo que observamos fue complejo y efectivo. La madre pudo guiar al joven ardillón fuera del peligro, y la estrategia estuvo bien planeada, ya que se retiraron a un árbol cercano donde la serpiente de cascabel estaría en desventaja. Se concluye que los ardillones de roca tienen un comportamiento bien desarrollado para proteger a sus crías contra los ataques de serpientes.
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