Nuevos registros y notas adicionales comentadas sobre la avifauna de la ciudad de Xalapa, Veracruz, México

El conocimiento detallado de la avifauna en una región constituye una valiosa base de datos que permite examinar cambios temporales de la riqueza y tamaños poblacionales de las especies, para actualizar su estado de conservación y desarrollar planes de manejo. El objetivo de este artículo es actualizar la lista de aves de la ciudad de Xalapa, Veracruz, México y aportar datos específicos y puntuales sobre los registros considerados como nuevos a lo previamente publicado por González-García et al. (2014). Añadimos 12 nuevos registros para la avifauna de la ciudad de Xalapa e incluimos a 48 especies con información que consideramos relevante para la zona urbana de la ciudad. Los nuevos registros añadidos son de dos especies residentes y de diez especies migratorias neotropicales (i.e., Anas clypeata, Aythya americana, Aythya collaris, Podiceps nigricollis, Botaurus lentiginosus, Elanoides forficatus, Laterallus ruber, Porzana carolina, Tringa solitaria, Chlidonias niger, Ridgwayia pinicola y Setophaga nigrescens). Tomando en cuenta estas aportaciones, el número total de especies de aves registradas en la zona urbana de Xalapa durante las últimas tres décadas asciende de 329 a 341.

Information on abundance and occurrence of two recently recorded species of ducks for Costa Rica

We present information about the relative abundance and occurrence of the Redhead (Aythya americana), and the Ruddy Duck (Oxyura jamaicensis) in Costa Rica. The observations were conducted during the winter seasons of 2010 to 2011, 2011 to 2012, and 2012 to 2013 at different wetlands across the country. These sightings represent the southernmost records for each species. What caused these birds to such southern latitudes is unknown, because the regular wintering areas of those species occur in northern Central America or Mexico.

Additional Data and Perspectives on Interspecific Aggression in the Common Loon, Gavia immer

We witnessed the killing of a female Redhead (Aythya Americana) by a male Common Loon (Gavia immer). The wound was delivered into the abdomen from below, and death occurred because of a torn, hemorrhaging liver. This same Common Loon also threatened a female Ring-necked Duck (Aythya collaris) with ducklings. We hypothesize that interspecific aggression by loons might be energetically costly but is sometimes adaptive because it deters predators.

The Alula and Its Aerodynamic Effect on Avian Flight

The alula, a small thumb-like appendage on a bird wing, is often credited with increasing lift and decreasing the risk of stall during bird flight. Using field based studies; researchers have observed that the alula lifts away from the wing at critical moments in flight, such as take-off and landing. However, to date, there has been no conclusive experimental evidence to support the idea that use of the alula affects lift. To determine the effect of the alula on avian flight, we used a wind tunnel to study the wings of four ducks: the Wood Duck (Aix sponsa), the Redhead Duck (Aythya americana), the Black Scoter (Melanitta americana), and the Lesser Scaup (Aythya affinis). We used a combination of lift/drag measurements and Particle Image Velocimetry (PIV) to test the wings at velocities from 10–16 m/s and angles of attack from −20 to 25 degrees. The alula was observed to naturally lift as the stall angle was approached. Of the four wings, the Black Scoter demonstrated the largest maximum lift coefficient (1.4), followed by the Wood Duck (1.3), the Lesser Scaup (1.2) and lastly, the Redhead Duck (0.9). All four wings had minimum drag coefficients near 0.1. The Lesser Scaup was the only wing which had a measurable change in lift (10%) attributable to alula deployment. PIV results for the flow field around the Lesser Scaup wing showed higher velocities on the top side of the wing when the alula was deflected.