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Palmer's agave (Agave palmeri), prominent in semi-desert grasslands of Arizona, New Mexico, and northwestern Mexico, shares its range with migratory nectar-feeding bat species and has bat-adapted floral traits. However, previous observations suggest that bats, such as Leptonycteris curasoae, often miss much of the lengthy flowering period of A. palmeri. To test the hypothesis that peak flowering coincides with peak availability of bats, I monitored flowering in 2 areas from mid June to mid September 1997, observed plants with night-vision binoculars for signs of pollinator activity, and measured floral rewards during part of this period. In the Peloncillos Mountains, New Mexico, no bat visits were seen during the first 60% of the flowering period (15 June to 12 August), and large dawn standing crops of nectar and pollen indicated little nocturnal consumption. From 24 August to 12 September, as the number of flowers decreased, bats were common visitors. These included L. curasoae and Choeronycteris mexicana. In the Chiricahua Mountains, Arizona, results were similar except that bats were also seen once in July. These observations suggest that most bats arrived late in the flowering period. However, detecting bats during peak flowering is problematic, because their energy needs are low relative to agave rewards, and a small population could be easily satiated.
The Devils River minnow (Dionda diaboli) has a limited distribution in Texas and Mexico. It is listed as threatened in the United States and endangered in Mexico. Recent collections in previously inaccessible locations in the headwaters of Pinto Creek, Kinney County, Texas, revealed a large population of D. diaboli. This species was found in habitats of flowing, spring-fed waters over gravel-cobble substrates, usually associated with aquatic macrophytes, but was confined to the upper segment of the creek. The confined distribution of Devils River minnow can offer valuable insight into its habitat and conservation. The future of this population might be threatened by reduced spring flows resulting from excessive pumping from the associated aquifer.
Monitoring wildlife populations is a challenging task for scientists and resource managers. We assessed 4 methods for monitoring population size of barking frogs (Eleutherodactylus augusti) in southern Arizona: mark-recapture, distance sampling, call counts, and visual encounter surveys. Because of the ecology and behavior of this species, all methods produced data that contained too much variability and bias to be useful for monitoring population size. For cryptic species such as barking frogs, monitoring programs might be more effective if they focus on parameters other than population size.
Several aquatic vertebrates have been introduced into freshwater systems in California over the past 100 years. Some populations of the two-striped garter snake (Thamnophis hammondii) have lived in sympatry with these species since their introduction; other populations have never encountered them. To assess the possible adaptation to a novel prey, we tested the predatory responses of T. hammondii from different populations to different chemosensory cues from native and introduced prey species. We presented chemical extracts from potential prey types and 2 control odors to individual snakes on cotton swabs and recorded the number of tongue flicks and attacks directed at each swab. Subject response was higher for prey odors than control substances. Odors from introduced centrarchid fish (Lepomis) elicited higher response levels than other prey types, including native anuran larvae (Pseudacris regilla). The pattern of response was similar for both populations of snakes (experienced and naïve, with respect to the introduced prey). We suggest that the generalist aquatic lifestyle of T. hammondii has allowed it to take advantage of increasing populations of introduced prey. Decisions on the management strategies for some of these introduced prey species should include consideration of how T. hammondii populations might respond in areas of sympatry.
The colubrid snake Tantilla equatoriana was described from 2 male specimens on the basis of several characters of color pattern and relatively high number of subcaudals. We examined the types and 3 additional specimens of T. equatoriana to assess whether the characters used to diagnose this taxon are unique or overlap with those of the highly variable, sympatric species T. melanocephala. Based on these data and a Principal Components Analysis of morphometric variation of T. equatoriana and T. melanocephala, we treat T. equatoriana as a junior synonym of T. melanocephala.
Reproductive data on the western cottonmouth, Agkistrodon piscivorus leucostoma, are scarce, generally incomplete, and usually based on pooled years for a given area. Current paradigms suggest that reproductive output in snakes can be influenced by local resource availability so temporal variation is important to document. Pregnant female western cottonmouths were collected for 3 consecutive years (2000–2002) from a lowland hardwood forest in northeastern Texas. This bottomland is exposed to flood pulses during winter that produce variable, but often large, amounts of prey for semi-aquatic snakes. Data recorded from 27 females indicated no difference in their snout-vent lengths (SVL) or masses among years. Of all reproductive traits, only clutch mass was correlated to female SVL and only in 1 year. Clutch mass and relative clutch mass varied temporally, suggesting reproductive output was influenced by prey availability. However, clutch size and mean offspring mass (that together comprise clutch mass) were both consistent among years. There was variation in mean offspring SVL and mass among females, and a negative correlation of both offspring characteristics to clutch size. These results suggest that the reproductive output of individual females might be responding to variation in prey availability in different ways (i.e., some by varying offspring number and others by modifying offspring size). Testing this hypothesis will require monitoring individual females for multiple years.
The cause of variability in quail recruitment in semiarid environments is unclear but variability is associated with precipitation. We hypothesized that variation in the protein and energy nutrition of hens, resulting from variation in the biomass of invertebrates in diets, causes variation in the proportion of reproductively active females in the population. We tested predictions of the hypothesis that: 1) reproducing female northern bobwhite (Colinus virginianus) will consume greater biomass of invertebrates than males and nonlaying females, and 2) the proportion of laying females is related to standing invertebrate biomass. Data were collected from 2 sites in the Gulf Coast Prairies (1992–1993) and 2 sites in the Rio Grande Plains (1993) of Texas. Diets of laying females had 3 to 12.5 times more invertebrates than diets of males and 2.3 to 4.0 times more invertebrates than diets of nonlaying females. Although the mean dry mass (kg/ha) of invertebrates was 2.0 to 5.5 times higher in the Gulf Coast Prairies than in the Rio Grande Plains, the percentage of females laying (60 to 73%) was similar between region-years. Other hypotheses regarding reproductive failure of female quail should be investigated.
To evaluate the hypothesis that spotted owls (Strix occidentalis) select habitats with cool microclimates to avoid high daytime temperatures, I sampled thermal regimes in nest areas used by Mexican spotted owls (S. o. lucida) in northern Arizona. I sampled air temperature at 30-min intervals in 30 pairs of nest and random sites from May through August and used the resulting thermal profiles to estimate a suite of diurnal temperature parameters. I estimated diurnal energy use and evaporative water loss, and compared these estimates and temperature parameters between nest and random areas. Owl nest areas were significantly cooler than random areas, and estimated evaporative water loss was significantly lower in nest areas than in random areas. In contrast, there was little difference in estimated diurnal energy use between nest and random areas. These results support the hypothesis that Mexican spotted owls select cool habitats. Use of these cooler habitats apparently reduces diurnal evaporative water loss relative to random areas, suggesting that water balance might be more important in habitat selection by spotted owls than previously realized. However, selection of cool nest areas apparently does not result in large energy savings, at least in this high-elevation study area (mean elevation at nest areas in this study was 2,230 m).
The brood-parasitic bronzed cowbird (Molothrus aeneus,) continues to expand its range in New Mexico and Texas. The current breeding range is 280 km outside of the historic breeding range. In Texas, spread rate increased from 6.22 km per year prior to 1956 to 13.75 km per year after 1956. Spread rate in New Mexico was constant at 12.72 km per year. Flight-range estimates based on fat indices of spring migrant cowbirds trapped at their northern range boundary in Texas suggest the potential for migration 341 km further north. We discuss factors that might limit or promote further range expansion.
Local species richness in shrew (Soricidae) assemblages is often high, and the mechanisms of ecological separation remain relatively unexplored. In this study, hair samples from 6 species of Sorex in 3 separate assemblages were analyzed for stable carbon (13C/12C) and nitrogen (15N/14N) isotope ratios to investigate dietary differences. At each locality, common species exhibited a broad range in δ15N and, to a lesser extent, δ13C, whereas non-overlapping signatures characterized the less abundant species. Because the naturally occurring stable isotope ratios of carbon and nitrogen vary with microenvironment and trophic level, the results support the idea that shrews achieve coexistence through resource partitioning. This study is the first to report stable isotope data on syntopic shrews and provides a direction for future research into resolving the mechanisms of ecological separation in shrew communities.
We used microhistological analysis of fecal pellets to identify plant species in diets of desert mule deer (Odocoileus hemionus eremicus) in southeastern California and to investigate seasonal changes in use of forage classes. We identified 34 taxa of plants, 7 of which have not been reported previously in the diets of desert mule deer. Browse species were abundant in diets during all seasons, but were lowest in spring, when forb species were most commonly observed. Use of succulents generally was low, with highest use occurring in autumn (3 to 24%). Grasses composed ≤1% of the diet in all seasons. Our findings emphasize the diversity of plant species used by desert mule deer and, consequently, the importance of conserving habitats that provide for that diversity.
Beginning in the 1960s, the familiar giant swallowtail (Papilo cresphontes) expanded its range into southern California from the east. From 1996 through 2003, at least 23 giant swallowtails were seen at 13 locations in the northern portion of the Baja California Peninsula, representing the first records of this species in the Mexican state of Baja California.
We compared levels of DDE contamination in the eggs of burrowing owls (Athene cunicularia) from the Imperial Valley of California in 2002 to levels detected in eggs collected at the same site in 1996. Levels of DDE ranged from 0.10 to 3.01 µg/g and were similar between years, suggesting a persistent, local source of contaminant for this resident population of owls.
In February 2000, we recorded mourning doves (Zenaida macroura) congregating at and drinking from a guzzler during nocturnal hours in the Chihuahuan Desert. Mourning doves might use nocturnal hours to maintain water balance in desert environments.
The first record of western yellow bat (Lasiurus xanthinus) for Nevada was found at the Moapa Valley National Wildlife Refuge, Muddy River, Clark County in January 1999. Year-round residence and an active breeding colony were verified through 2000. Roosting and foraging seems concentrated within extensive California fan palm groves throughout the upper Moapa Valley. Capture and acoustic sampling showed this to be the second-most abundant species in the valley. The diet included Coleoptera, Diptera, Hemiptera, Homoptera, Lepidoptera, and Orthoptera. This record represents the northernmost distribution of the species.
We examined specimens of 3 species of rodents, which represent new records in the State of Colima, Mexico. This includes Reithrodontomys hirsutus, which had not been collected in more than 50 years, and the third recorded specimen of Reithrodontomys mexicanus riparius from western México and formerly considered restricted to the State of Michoacán.
Tree climbing behavior is rarely observed among the Canidae and has not been observed in kit foxes (Vulpes macrotis). While conducting another behavioral study in Bakersfield, California in November 2002, we observed kit foxes climb trees on 2 occasions. Our observations demonstrate that kit foxes are capable of climbing trees and of agile mobility among tree branches. Our observations also provide an example of the behavioral plasticity of kit foxes, a characteristic that might contribute to their ability to successfully inhabit anthropogenically altered environments.
We report new records of collared peccary (Pecari tajacu) in New Mexico that document its continued northward expansion in the United States, in general, and in northwestern New Mexico, in particular. These records might represent the northernmost extent of its range in the Southwest. Collared peccaries in New Mexico typically occur in desert, rocky, and brushy foothill regions and riparian communities. On the Zuni Indian Reservation, animals were observed at elevations up to 2,335 m in piñon-juniper and ponderosa pine habitats. Climate might play an important role in range expansion and contraction as collared peccaries might migrate north during years of drought or mild winters in search of food or new habitat.
Terrestrial habitats of Richland Creek Wildlife Management Area, Texas, were surveyed for vertebrate diversity in 1998 and 1999. During the 2-year sampling period, 10 species of amphibians, 20 species of reptiles, and 23 species of mammals were collected or observed. These actions represent an effort of Texas Parks and Wildlife to inventory the fauna of state-owned property. This information will begin to form a baseline to assess future management decisions.
Additions to the archaeological fauna recovered from the former Chinatown section in El Paso, Texas (late 1800s), include lizard, ringtail, dog, killdeer, domestic goose, badger, domestic cat, jackrabbit, and cottontail. The latter 5 species likely were used for food. Two species of turtles used as food also are discussed.