Genetic variability and population structure of the Montezuma quail (Cyrtonyx montezumae) in the northern limit of its distribution.

Restricted movement among populations decreases genetic variation, which may be the case for the Montezuma quail (Cyrtonyx montezumae), a small game bird that rarely flies long distances. In the northern limit of its distribution, it inhabits oak-juniper-pine savannas of Arizona, New Mexico, and Texas. Understanding genetic structure can provide information about the demographic history of populations that is also important for conservation and management. The objective of this study was to determine patterns of genetic variation in Montezuma quail populations using nine DNA microsatellite loci. We genotyped 119 individuals from four study populations: Arizona, Western New Mexico, Central New Mexico, and West Texas. Compared to other quail, heterozygosity was low (H¯0 = 0.22 ± 0.04) and there were fewer alleles per locus (A = 2.41 ± 0.27). The global population genetic differentiation index RST = 0.045 suggests little genetic structure, even though a Bayesian allocation analysis suggested three genetic clusters (K = 3). This analysis also suggested admixture between clusters. Nevertheless, an isolation-by-distance analysis indicates a strong correlation (r = 0.937) and moderate evidence (P = 0.032) of non-independence between geographical and genetic distances. Climate change projections indicate an increase in aridity for this region, especially in temperate ecosystems where the species occurs. In this scenario, corridors between the populations may disappear, thus causing their complete isolation.

Agriculture creates subtle genetic structure among migratory and nonmigratory populations of burrowing owls throughout North America.

Population structure across a species distribution primarily reflects historical, ecological, and evolutionary processes. However, large-scale contemporaneous changes in land use have the potential to create changes in habitat quality and thereby cause changes in gene flow, population structure, and distributions. As such, land-use changes in one portion of a species range may explain declines in other portions of their range. For example, many burrowing owl populations have declined or become extirpated near the northern edge of the species' breeding distribution during the second half of the 20th century. In the same period, large extensions of thornscrub were converted to irrigated agriculture in northwestern Mexico. These irrigated areas may now support the highest densities of burrowing owls in North America. We tested the hypothesis that burrowing owls that colonized this recently created owl habitat in northwestern Mexico originated from declining migratory populations from the northern portion of the species' range (migration-driven breeding dispersal whereby long-distance migrants from Canada and the United States became year-round residents in the newly created irrigated agriculture areas in Mexico). We used 10 novel microsatellite markers to genotype 1,560 owls from 36 study locations in Canada, Mexico, and the United States. We found that burrowing owl populations are practically panmictic throughout the entire North American breeding range. However, an analysis of molecular variance provided some evidence that burrowing owl populations in northwestern Mexico and Canada together are more genetically differentiated from the rest of the populations in the breeding range, lending some support to our migration-driven breeding dispersal hypothesis. We found evidence of subtle genetic differentiation associated with irrigated agricultural areas in southern Sonora and Sinaloa in northwestern Mexico. Our results suggest that land use can produce location-specific population dynamics leading to subtle genetic structure even in the absence of dispersal barriers.

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.

Population density of the western burrowing owl (Athene cunicularia hypugaea) in Mexican prairie dog (Cynomys mexicanus) colonies in northeastern Mexico.

BACKGROUND: The western burrowing owl (Athene cunicularia hypugaea) occurs throughout western North America in various habitats such as desert, short-grass prairie and shrub-steppe, among others, where the main threat for this species is habitat loss. Range-wide declines have prompted a need for reliable estimates of its populations in Mexico, where the size of resident and migratory populations remain unknown. RESULTS: Our objective was to estimate the abundance and density of breeding western burrowing owl populations in Mexican prairie dog (Cynomys mexicanus) colonies in two sites located within the Chihuahuan Desert ecoregion in the states of Nuevo Leon and San Luis Potosi, Mexico. Line transect surveys were conducted from February to April of 2010 and 2011. Fifty 60 ha transects were analyzed using distance sampling to estimate owl and Mexican prairie dog populations. We estimated a population of 2026 owls (95 % CI 1756-2336) in 2010 and 2015 owls (95 % CI 1573-2317) in 2011 across 50 Mexican prairie dog colonies (20,529 ha). CONCLUSIONS: The results represent the first systematic attempt to provide reliable evidence related to the size of the adult owl populations, within the largest and best preserved Mexican prairie dog colonies in Mexico.

Dispersal and oviposition of laboratory-reared gravid females of Toxorhynchites moctezuma in an arid urban area of Sonora, Mexico.

Dengue is a serious public health problem worldwide. Biological control of its vector, Aedes aegypti, remains a feasible option in light of increasing urbanization and insecticide resistance. We studied the dispersal and oviposition activity of Toxorhynchites moctezuma in a dengue-endemic urban area in SSonora, Mexico, to provide information about the potential of Toxorhynchites as a control agent for Ae. aegypti in arid areas. We released 210 and 100 laboratory-reared gravid females of Tx. moctezuma in 2 city blocks during the summer and fall of 1993. We set 3 1-liter containers and 1 car tire as sentinel traps at each of 10 backyards within each city block. Spatial and temporal patterns of dispersal and oviposition activity differed between city blocks and between releases. However, a Cox regression analysis showed no significant difference in the per-day probability of Tx. moctezuma oviposition events in sentinel traps between summer and fall releases. Per-day oviposition probability was nearly 5 times greater for sentineltraps that contained larvae of Ae. aegypti, suggesting a high specificity of the predator for its prey. The proportion of sentinel traps positive for Tx. moctezuma eggs did not increase substantially after the 8th day piost-release, reaching 66% and 23% for sentinel traps with and without Ae. aegypti larvae, respectively.