How birds age? Chilean Elaenia as an example for the Neotropical bird species
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ORIGINAL ARTICLE
How birds age? Chilean Elaenia as an example for the Neotropical bird species Cristian A. Gorosito 1 & Joaquín Cereghetti 2 & Víctor R. Cueto 1 Received: 25 March 2020 / Revised: 16 June 2020 / Accepted: 3 July 2020 # Sociedade Brasileira de Ornitologia 2020
Abstract Determining the age of birds is important to understand the demographic dynamic, since the effects of mortality factors may depend on the age of the individuals. Several methods have been used to determine the age of many European and North American bird species, but little is known about aging in Neotropical birds. The aim of our research was to evaluate the method for aging Chilean Elaenia (Elaenia chilensis) through individuals of known age. We used the palate color and feather molt limits of individuals of known age, together with the previously available proposals for aging this species to propose a new criterion for determining the age of Chilean Elaenias. Our criterion makes possible to differentiate adult individuals in the first, second, and third year since their born. We consider that our proposal will allow to advance towards more detailed research on the population dynamics of bird species in South America. Keywords Age determination . Elaenia chilensis . Molt pattern . Palate color . Patagonia
Introduction The age of individuals in a population is central to understand the demographic dynamic, because the influence and magnitude of mortality factors may depend on the bird’s age (Newton 1998). For example, individuals of migratory bird species that make their first trip have higher mortality rates than older individuals (Faaborg et al. 2010). In Europe and North America, several methods have been described to determine the age of full-grown birds of many species. These methods included morphological characters, molt patterns (affecting color, shape, and wear of feathers), skull ossification, tongue marks, or the color of bare parts, such as bill and legs (Svensson 1992; Pyle 1997). In Neotropical birds, little is known about their aging (Ryder
Communicated by: Leandro Bugoni. * Víctor R. Cueto [email protected] 1
Centro de Investigación Esquel de Montaña y Estepa Patagónica (CIEMEP), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) y Universidad Nacional de la Patagonia San Juan Bosco, Roca 780, U9200 Esquel, Chubut, Argentina
2
Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa, Santa Rosa, La Pampa, Argentina
and Wolfe 2009; Wolfe and Pyle 2012), although in the last years, there has been an increase in the studies of molt patterns and aging (Rueda-Hernández et al. 2018). For example, Pyle et al. (2015) give a comprehensive evaluation of those patterns for northern Chilean species, and Johnson and Wolfe (2018) provide an exhaustive evaluation of molt patterns and aging criteria for Amazonian species. Chilean Elaenia (Elaenia chilensis) is the most abundant bird species in the Andean-Patagonian Forest between October and March (Ippi et al. 2009; Cueto and Gorosito 20
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