Arvind O. Panjabi

Association of Habitat Characteristics with Winter Survival of a Declining Grassland Bird in Chihuahuan Desert Grasslands of Mexico

ABSTRACT. Grassland bird populations have shown persistent declines over the past four decades in North America. Possible explanations for the declines include decreased winter survival because of habitat deterioration. To address this hypothesis, we evaluated the relationship between habitat structure and winter survival of Vesper Sparrows (Pooecetes gramineus) in Chihuahuan Desert grasslands of northern Mexico. We radiotagged and monitored the survival of 102 individuals during the winters of 2009 and 2010. We obtained visual estimates of vegetation structure and composition at every individuals radiotelemetry location. We used an exponential regression model to estimate daily survival rates and determine the association between habitat structure and survival. We estimated a daily winter survival probability of 99.1% (95% confidence interval: 97.4–99.7%) for Vesper Sparrows in both years. Our survival analysis suggests that habitat structure is an important predictor of winter survival. Average grass height and shrub height were positively related to Vesper Sparrow survival. Our results suggest that grassland bird populations may be negatively affected by poor grassland conditions during the winter and that low winter survival may be an important factor in population declines. Winter habitat conditions in the Chihuahuan Desert grasslands are shaped primarily by grazing and climate, highlighting the need to improve range management, especially in Mexico, as a means to reverse persistent population declines of grassland birds.

The Imminent Disappearance of the Aplomado Falcon from the Chihuahuan Desert

Desaparicion Inminente de Falco femoralis Del Desierto Chihuahuense Seguimos la ocupacion territorial de Falco femoralis durante un periodo de 12 anos (2003–2014) en el centro de Chihuahua, Mexico, bajo condiciones de sequia severa y destruccion de su habitat de anidamiento. La conversion de los territorios de cria de los halcones a tierras agricolas ha destruido hasta ahora 17 de los 35 territorios de cria ocupados por parejas de F. femoralis conocidos al menos una vez desde el ano 2000. Solo una pequena fraccion territorio de los restantes fue ocupada en 2014. La desaparicion de los halcones de los territorios de cria antiguos que se mantienen intactos sugiere un deficit de reclutamiento causado por tasas reproductivas bajas relacionadas con una disminucion general en la calidad de los pastizales y en la cantidad de presas. La persistencia de unas pocas parejas sugiere que la poblacion se mantiene actualmente por la elevada supervivencia de los adultos mas que por su fertilidad. Esta tendencia, asi como...

Seed size, bill morphology, and handling time influence preferences for native vs. nonnative grass seeds in three declining sparrows

ABSTRACT The invasion of exotic grasses is a potential threat to the winter habitat of migratory grassland birds by reducing native sources of seed food. We compared seed preferences among 3 native (blue grama [Bouteloua gracilis], sideoats grama [Bouteloua curtipendula], and green sprangletop [Leptochloa dubia]), and 3 exotic (Lehmann lovegrass [Eragrostis lehmanniana], buffelgrass [Pennisetum ciliare], and natal grass [Melinis repens]) grass seeds in captive Bairds (Ammodramus bairdii), Grasshopper (A. savannarum), and Savannah (Passerculus sandwichensis) sparrows to investigate factors that determine vulnerability of grassland passerines to exotic grasses in the Chihuahuan Desert. We hypothesized that seed handling time would determine the ability of sparrows to exploit exotic grass seeds, and that larger-billed birds would be able to better exploit a larger variety of seeds, including exotic seeds. We offered seeds in choice and nonchoice trials and determined handling times for the different seed and bird species. The results indicate that handling time in relation to seed size determined seed preferences. Sparrows preferred seeds they could handle more efficiently to maximize energy intake over time. Bairds and Savannah sparrows, with intermediate and small bill sizes, respectively, preferred natal grass seeds of intermediate size and short handling time, and Grasshopper Sparrows, with the largest bill, preferred the larger sideoats grama seeds. Lehmann lovegrass, the smallest seed with intermediate handling time, was avoided by the 3 sparrows. Buffelgrass, the largest seed with the longest handling time, was avoided by Bairds and Savannah sparrows. Blue grama, the second-smallest seed with relative short handling time, was neither preferred nor avoided, and green sprangletop, an intermediate-sized seed with a relatively longer handling time, was avoided in the choice trials but consumed in the nonchoice trials. These results indicate that exotic grass seeds may be a source of food for 3 sparrows wintering in the Chihuahuan Desert, provided they can be handled efficiently. Our results also show, however, that wintering grassland sparrows are probably unable to consume sufficient buffelgrass and Lehmann lovegrass seeds to meet daily energy requirements, indicating that these grasses may be a threat by reducing exploitable sources of seed food.

Density and population estimates of Rose-bellied Bunting (Passerina rositae), Cinnamon-tailed Sparrow (Peucaea sumichrasti), and Orange-breasted Bunting (Passerina lechlancherii) in the Sierra Tolistoque, Oaxaca, Mexico

ABSTRACT Micro-endemic species are at greater risk of extinction because of their small populations and limited distribution. We conducted a breeding population survey of 3 little-known Mexican endemic bird species: Rose-bellied Bunting (Passerina rositae), Cinnamon-tailed Sparrow (Peucaea sumichrasti), and Orange-breasted Bunting (Passerina lechlancherii) in Sierra Tolistoque, Oaxaca. The purpose of the survey was to (a) determine the population density and size of these 3 species in the Sierra Tolistoque, (b) estimate the relative importance of various landscape features for each species, and (c) provide more rigorous scientific information to aid in the conservation and management of these species. In the case of Rose-bellied Bunting, we aimed to assess whether it prefers ravines over other landscape types during the breeding seasons, as stated in previous studies. Between late May and June 2012, we conducted point counts (n = 209) throughout the southern slope of the Sierra Tolistoque on the Pacific slope of the Isthmus of Tehuantepec, in Oaxaca, Mexico. Overall bird density was 0.98 birds/ha for Rose-bellied Bunting, 0.547 birds/ha for Orange-breasted Bunting, and 0.514 birds/ha for Cinnamon-tailed Sparrow. The estimated population in each landscape category showed that despite the existence of subtle interspecific preferences, hillsides are the major reservoirs for the 3 species. Rose-bellied Bunting did not occur in greater density in ravines compared to hillsides, which comprised more than twice the area of ravines. The importance of the Sierra Tolistoque for the long-term conservation of the 2 micro-endemic species is crucial considering our population estimates suggest that ∼30% of the estimated world population of Rose-bellied Bunting and Cinnamon-tailed Sparrow are found within the range of the Sierra Tolistoque.

Molecular analysis of stomach contents reveals important grass seeds in the winter diet of Baird's and Grasshopper sparrows, two declining grassland bird species

We analyzed the diet of Baird’s Sparrow (Ammodramus bairdii) and Grasshopper Sparrow (A. savannarum) in three different sites and sampling periods across the Chihuahuan Desert in northern Mexico. DNA from seeds in regurgitated stomach contents was sequenced using NGS technology and identified with a barcoding approach using the P6 loop of the trnL intron as genetic marker. During each sampling period, we collected random soil samples to estimate seed availability in the soil seed bank. Due to the variability and size of the genetic marker, the resolution was limited to a family level resolution for taxonomic classification of seeds, but in several cases a genus level was achieved. Diets contained a high diversity of seeds but were dominated by a limited number of genera/families. Seeds from Panicoideae (from the genera Panicum, Setaria, Eriochloa, Botriochloa, and Hackelochloa) contributed for the largest part to the diets (53 ± 19%), followed by Bouteloua (10 ± 12%). Depending on the site and sampling period, other important seeds in the diets were Eragrostideae, Pleuraphis, Asteraceae, Verbena, and Amaranthus. The most abundant seeds were not always preferred. Aristida and Chloris were common in the soil seed bank but these seeds were avoided by both bird species. Baird’s and Grasshopper sparrows did not differ in seed preferences. This work highlights the importance of range management practices that favor seed production of Panicoideae and Bouteloua grasses to enhance winter habitat use and survival of Baird’s and Grasshopper sparrows in the Chihuahuan Desert.

Primer development for amplification of toll-like genes for the assessment of adaptive genetic diversity in vulnerable grassland bird species

Assessing genetic diversity in species of conservation concern is a critical parameter to implement management plans that may increase their viability. Traditionally, genetic diversity has been assessed using neutral genes; nevertheless, recent perspectives have proposed that genetic variation under natural selection (adaptive genes) is more representative of the adaptive potential of a population or species. Toll-like receptors (TLR) are an innate immune gene family that binds to Pathogen Associated Molecular Patterns. These receptors evolved under positive selection and by coevolution; therefore, they represent adaptive genetic diversity. We designed and tested six pairs of primers that amplify TLR genes in seven grassland species, one of the most vulnerable North American bird groups. Analysis of the sequences showed that all were polymorphic and evolved under positive selection, with the exception of TLR3, which evolved neutrally. These primers may constitute a useful tool for conservation studies for grassland sparrow species.

HOME RANGE AND HABITAT USE OF WINTERING VESPER SPARROWS IN GRASSLANDS OF THE CHIHUAHUAN DESERT IN MEXICO

Abstract Grassland birds are declining at an alarming rate and habitat limitation on the wintering grounds may play a major role in population declines. In an attempt to understand habitat needs and constraints of grassland bird species on their wintering grounds, we conducted the first-ever telemetry study to document the movements of a wintering grassland passerine bird in grasslands of the Chihuahuan Desert in northern Mexico. We attached radio-transmitters to 99 Vesper Sparrows in January of 2009 and 2010 and tracked them for up to 51 days. We estimated vegetation characteristics at foraging, roosting and random locations. We used kernel density estimators of the utilization distribution for each individual sparrow to estimate home range size. We found differences in average home range size between 2009 and 2010 (108.46 ± 36.43 ha and 30.91 ± 4.74 ha, respectively). Home ranges showed high levels of intraspecific overlap, with average pairwise overlap of 0.41, 0.70 and 0.79 among individuals at three study sites, as measured by the Bhattacharyyas affinity. Grasses and shrubs were shorter in foraging locations than in random sites within Vesper Sparrow core habitat, but we found no differences in grass cover and shrub cover. We suggest that movements of Vesper Sparrows are mostly limited to <1 km2 during the winter and hypothesize that these movements are subject to constraints by food limitation and predation.