Climate complexity in the migratory cycle of Ammodramus bairdii

Abstract One way to understand the ecology of bird migration is to analyze how birds use their ecological niche during their annual cycle. Ammodramus bairdii is a grassland specialist sparrow that breeds in southern Canada and the northern U.S.A. and winters in the Chihuahuan Desert. A continuous and alarming decrease of its populations has been observed over the last 50 years, and studying its seasonal distribution and associated climatic niches could help improve strategies for its conservation. We analyzed the temporal use of its Grinnellian niche (GN) -set of environmental conditions under which a species can establish and persist; in this case the climatic attributes-. We modeled the GN for the reproductive and winter seasons and projected them onto each other (inter-prediction), and also onto transient migratory periods. To measure niche breadth and their overlap, minimum convex polygons (MCP) were calculated for the climatic space. The niches of each of the two seasons were tested for similarity using the PCA axes of climatic variables. The geographic areas with optimal, suboptimal and marginal conditions were identified, based on the distance to the centroid of the GN. The models for each season revealed no geographic inter-prediction among them, with the exception of winter to migratory seasons. The niche breadth of the winter was greater than that of the reproductive season, with an overlap of 22.47% and 45.18%, respectively. The similarity analyses showed a value of zero between seasons. The climate conditions for the records during the migratory months corresponded with suboptimal and marginal conditions of the sparrow’s winter niche. These results suggest that A. bairdii uses different climate conditions within ecological niches of each season during its migratory cycle

Winter diet of the long-eared owl Asio otus (Strigiformes: Strigidae) in the grasslands of Janos, Chihuahua, Mexico

Abstract Background: The long-eared owl (Asio otus) has a Holarctic distribution, including much of North America. This nocturnal species is considered to be extremely secretive, and poorly known in the Great Plains of the United States and Canada, as well as to México, where no previous studies on its diet have been conducted. Findings: We analyzed 120 pellets collected during January 2007 in roosts in a 2–3 m height mesquite scrub within a grassland area of Reserva Ecológica El Uno, located in the Natural Protected Area Janos. We registered and identified three orders, four families, eight genera and ten species of mammals and two orders and one family of insects. Winter diet is dominated by mammals, especially rodents in both frequency and biomass. Cricetidae and Perognathus flavus were the most frequent family and species, respectively. On the other hand, when analyzing biomass, Sigmodon species were dominant, achieving almost 70% of the consumed biomass. Levin's standardized niche breath based on frequency was calculated as 0.40, while based on biomass was 0.38. Also, two previously unrecorded rodent species were identified as long-eared owl prey. Conclusion: Although 18 different types of items were identified, the long-eared owl tends to be selective, with a single genera (Sigmodon) comprising almost 70% of its consumed biomass during winter. Perognathus flavus was also important in frequency (21%); however, it barely constitutes 2% of the consumed biomass. Keywords: Winter diet, Long-eared owl, Grasslands, Janos, México Resumen El búho orejas largas es una especie Holártica, que se distribuye en gran parte de Norteamérica y que ha sido poco estudiada, especialmente en las Grandes Planicies de Estados Unidos y en México, donde no existe un estudio previo sobre su dieta invernal. Se colectaron y analizaron 120 egagrópilas en la Reserva Ecológica El Uno, dentro del Área Natural Protegida Reserva de la Biósfera Janos. Se identificaron un total de 18 tipos de presa, pero la especie mostró selectividad por dos géneros/especies, ya que cerca del 70% de la biomasa consumida fueron especies del género Sigmodon, mientras que el 21% de las muestras contenían Perognathus flavus. Además, dos especies de roedores identificadas constituyen nuevos registros de presa para la especie

Análisis jerárquico de la comunidad de aves asociada al hábitat ribereño dominado por taxodium mucronatum en el Río Sabinas, Coahuila de Zaragoza, México.

Las zonas ribereñas han sido identificadas como hábitats clave para la vida silvestre, especialmente para el paisaje árido de Norteamérica; sin embargo en el norte de México dichas zonas han sido poco estudiadas. El presente estudio se llevó a cabo en el hábitat ribereño dominado por sabinos (Taxodium mucronatum) del Río Sabinas, Coahuila, México, de diciembre de 2004 a agosto de 2006. Se abordó el tema de la comunidad anual de aves desde un análisis por secciones y el de la comunidad reproductiva desde un enfoque jerárquico, donde los fragmentos de vegetación ribereña son la escala blanco, pero incluyendo en el análisis una escala menor (estructura y variables del hábitat) y una escala mayor (variables del paisaje), que permitan tener un panorama más amplio de los factores que afectan a las ave

Climate complexity in the migratory cycle of Ammodramus bairdii.

One way to understand the ecology of bird migration is to analyze how birds use their ecological niche during their annual cycle. Ammodramus bairdii is a grassland specialist sparrow that breeds in southern Canada and the northern U.S.A. and winters in the Chihuahuan Desert. A continuous and alarming decrease of its populations has been observed over the last 50 years, and studying its seasonal distribution and associated climatic niches could help improve strategies for its conservation. We analyzed the temporal use of its Grinnellian niche (GN) -set of environmental conditions under which a species can establish and persist; in this case the climatic attributes-. We modeled the GN for the reproductive and winter seasons and projected them onto each other (inter-prediction), and also onto transient migratory periods. To measure niche breadth and their overlap, minimum convex polygons (MCP) were calculated for the climatic space. The niches of each of the two seasons were tested for similarity using the PCA axes of climatic variables. The geographic areas with optimal, suboptimal and marginal conditions were identified, based on the distance to the centroid of the GN. The models for each season revealed no geographic inter-prediction among them, with the exception of winter to migratory seasons. The niche breadth of the winter was greater than that of the reproductive season, with an overlap of 22.47% and 45.18%, respectively. The similarity analyses showed a value of zero between seasons. The climate conditions for the records during the migratory months corresponded with suboptimal and marginal conditions of the sparrow's winter niche. These results suggest that A. bairdii uses different climate conditions within ecological niches of each season during its migratory cycle

Parasite prevalence in Worthen’s Sparrow (Spizella wortheni): Mexican endemic and endangered species

The Worthen’s sparrow is an endemic bird of the Mexican Plateau that due to its limited distribution and population size is considered to be endangered, both nationally and globally. In general, species at risk have been, at least historically, under population size and genetic diversity reductions, which are factors that can act together to increase infections risk and susceptibility. Therefore, with the purpose to determine such propensity in this species, we analyzed the intestinal parasitic infection through fecal samples from 11 individuals, and hemoparasites, hematocrit and differential leukocyte quantification from one sample. Results indicated that 91% of the samples had one parasite taxon, with genus Cryptosporidium showing the highest prevalence (64%), followed by Eimeria (55%), and Ascaridia (9%). However, mean values of oocysts/eggs per gram indicated a low parasitic infection. We found no blood parasites, and the white blood cell counts were among reference values for other sparrow species

Winter diet of Burrowing Owls in the Llano La Soledad, Galeana, Nuevo León, México

The dietary niche breadth of the Burrowing Owl was determined (Athene cunicularia Molina, 1782) in Llano La Soledad, Galeana, Nuevo Leon in northern Mexico, by considering prey type, numerical percentage, weight, weight percentage, frequency of occurrence percentage, and IRI percentage. The study compared data from three winters (2002–2003, 2003–2004, 2004–2005) by analyzing 358 pellets, identifying 850 prey items. Invertebrates constituted 90% of prey items, which mostly included insects (85%); beetles were the most common insects found in pellets (70%). Vertebrates made up 84% of consumed weight, of which 83% were mammals. Most of the mammals were cricetid rodents (41%). Niche breadth based on the numerical and weight percentage confirmed the Burrowing Owl as a generalist species with mean values per year ranging between 0.65 and 0.82. Additionally, there was a strong association between the weight of rodent species in winter. This association was mainly driven by changes in composition and frequency of these prey species during the second winter, probably caused by high annual rainfall. The second season also showed a statistically significant narrower niche (Ro = 0.96) and the smallest overlap (0.45 vs. 0.76) among the three winters

Adaptive genetic diversity and evidence of population genetic structure in the endangered Sierra Madre Sparrow (Xenospiza baileyi).

The magnitude and distribution of genetic diversity through space and time can provide useful information relating to evolutionary potential and conservation status in threatened species. In assessing genetic diversity in species that are of conservation concern, several studies have focused on the use of Toll-like receptors (TLRs). TLRs are innate immune genes related to pathogen resistance, and polymorphisms may reflect not only levels of functional diversity, but may also be used to assess genetic diversity within and among populations. Here, we combined four potentially adaptive markers (TLRs) with one mitochondrial (COI) marker to evaluate genetic variation in the endangered Sierra Madre Sparrow (Xenospiza baileyi). This species offers an ideal model to investigate population and evolutionary genetic processes that may be occurring in a habitat restricted endangered species with disjunct populations (Mexico City and Durango), the census sizes of which differ by an order of magnitude. TLRs diversity in the Sierra Madre Sparrow was relatively high, which was not expected given its two small, geographically isolated populations. Genetic diversity was different (but not significantly so) between the two populations, with less diversity seen in the smaller Durango population. Population genetic structure between populations was due to isolation and different selective forces acting on different TLRs; population structure was also evident in COI. Reduction of genetic diversity in COI was observed over 20 years in the Durango population, a result likely caused by habitat loss, a factor which may be the main cause of diversity decline generally. Our results provide information related to the ways in which adaptive variation can be altered by demographic changes due to human-mediated habitat alterations. Furthermore, our findings may help to guide conservation schemes for both populations and their restricted habitat