Paul A. Heady

Bat response to differing fire severity in mixed-conifer forest California, USA.

Wildlife response to natural disturbances such as fire is of conservation concern to managers, policy makers, and scientists, yet information is scant beyond a few well-studied groups (e.g., birds, small mammals). We examined the effects of wildfire severity on bats, a taxon of high conservation concern, at both the stand (<1 ha) and landscape scale in response to the 2002 McNally fire in the Sierra Nevada region of California, USA. One year after fire, we conducted surveys of echolocation activity at 14 survey locations, stratified in riparian and upland habitat, in mixed-conifer forest habitats spanning three levels of burn severity: unburned, moderate, and high. Bat activity in burned areas was either equivalent or higher than in unburned stands for all six phonic groups measured, with four groups having significantly greater activity in at least one burn severity level. Evidence of differentiation between fire severities was observed with some Myotis species having higher levels of activity in stands of high-severity burn. Larger-bodied bats, typically adapted to more open habitat, showed no response to fire. We found differential use of riparian and upland habitats among the phonic groups, yet no interaction of habitat type by fire severity was found. Extent of high-severity fire damage in the landscape had no effect on activity of bats in unburned sites suggesting no landscape effect of fire on foraging site selection and emphasizing stand-scale conditions driving bat activity. Results from this fire in mixed-conifer forests of California suggest that bats are resilient to landscape-scale fire and that some species are preferentially selecting burned areas for foraging, perhaps facilitated by reduced clutter and increased post-fire availability of prey and roosts.

Nestedness of desert bat assemblages: species composition patterns in insular and terrestrial landscapes

Nested patterns of community composition exist when species at depauperate sites are subsets of those occurring at sites with more species. Nested subset analysis provides a framework for analyzing species occurrences to determine non-random patterns in community composition and potentially identify mechanisms that may shape faunal assemblages. We examined nested subset structure of desert bat assemblages on 20 islands in the southern Gulf of California and at 27 sites along the Baja California peninsula coast, the presumable source pool for the insular faunas. Nested structure was analyzed using a conservative null model that accounts for expected variation in species richness and species incidence across sites (fixed row and column totals). Associations of nestedness and island traits, such as size and isolation, as well as species traits related to mobility, were assessed to determine the potential role of differential extinction and immigration abilities as mechanisms of nestedness. Bat faunas were significantly nested in both the insular and terrestrial landscape and island size was significantly correlated with nested structure, such that species on smaller islands tended to be subsets of species on larger islands, suggesting that differential extinction vulnerabilities may be important in shaping insular bat faunas. The role of species mobility and immigration abilities is less clearly associated with nestedness in this system. Nestedness in the terrestrial landscape is likely due to stochastic processes related to random placement of individuals and this may also influence nested patterns on islands, but additional data on abundances will be necessary to distinguish among these potential mechanisms.

Insectivorous Bat Pollinates Columnar Cactus More Effectively per Visit than Specialized Nectar Bat

Plant-pollinator interactions are great model systems to investigate mutualistic relationships. We compared pollinator effectiveness between facultative and obligate nectar-feeding bats to determine how foraging specialization influences mutualistic interactions in a bat-adapted cactus. We predicted that a specialized nectarivorous bat would deliver more pollen than an opportunistic nectar-feeding bat because of specialized adaptations to nectar feeding that indicate close association with their food plants. Counter to our predictions, the opportunistic Antrozous pallidus delivered significantly more pollen grains per visit than the specialized Leptonycteris yerbabuenae. Higher pollinator effectiveness, based on visitation rates and pollen deposition levels, varied between species by site, and although A. pallidus visits flowers much less frequently than L. yerbabuenae over all sites, it is likely an effective and reliable pollinator of Pachycereus pringlei in Baja, Mexico. Our results suggest that morphological adaptations and dietary specialization on nectar do not necessarily confer advantages for pollination over less specialized plant visitors and highlight the reciprocally exploitative nature of mutualisms.

Facultative Nectar-Feeding Behavior in a Gleaning Insectivorous Bat (Antrozous pallidus)

Abstract Foraging plasticity that includes facultative nectarivory is extremely rare in temperate insectivorous bats. We investigated flower-visiting behavior of pallid bats (Antrozous pallidus, Vespertilionidae) to bat-adapted flowers of cardon cacti (Pachycereus pringlei) to determine whether pallid bats consume floral nectar or visit flowers to opportunistically glean insects attracted to flowers. In 2007 and 2008, we recorded flower-visiting behavior of bats using infrared videography on 143 cactus-nights across 14 sites in Baja California, Mexico. Pallid bats were regular visitors to cardon flowers and consumed floral nectar by plunging their faces into the corolla to lap pooled nectar. We recorded 1,198 flower visits by A. pallidus, which accounted for 10% of visits to flowers by all bats. Pallid bats visited flowers on 57% of cactus-night observations (n  =  81/143) and 52% (n  =  28/54) of captured bats had visible pollen loads. Flower-visiting activity by A. pallidus was concentrated early in the evening where nectarivorous Mexican lesser long-nosed bats (Leptonycteris yerbabuenae [ =  curasoae], Phyllostomidae) were present, but more evenly distributed throughout the night at sites without L. yerbabuenae, suggesting potential competitive exclusion among these nocturnal chiropteran pollinators.

Seasonal reliance on nectar by an insectivorous bat revealed by stable isotopes

Many animals have seasonally plastic diets to take advantage of seasonally abundant plant resources, such as fruit or nectar. Switches from insectivorous diets that are protein rich to fruits or nectar that are carbohydrate rich present physiological challenges, but are routinely done by insectivorous songbirds during migration. In contrast, insectivorous bat species are not known to switch diets to consume fruit or nectar. Here, we use carbon stable isotope ratios to establish the first known case of a temperate bat species consuming substantial quantities of nectar during spring. We show that pallid bats (Antrozous pallidus) switch from a diet indistinguishable from that of sympatric insectivorous bat species in winter (when no cactus nectar is present) to a diet intermediate between those of insectivorous bats and nectarivorous bats during the spring bloom of a bat-adapted cactus species. Combined with previous results that established that pallid bats are effective pollinators of the cardon cactus (Pachycereus pringlei), our results suggest that the interaction between pallid bats and cardon cacti represents the first-known plant-pollinator mutualism between a plant and a temperate bat. Diet plasticity in pallid bats raises questions about the degree of physiological adaptations of insectivorous bats for incorporation of carbohydrate-rich foods, such as nectar or fruit, into the diet.

Using behavioral and stable isotope data to quantify rare dietary plasticity in a temperate bat

Seasonal reliance on plant-based resources is very uncommon in temperate insectivorous bats. The pallid bat (Antrozous pallidus) is an exception and in the Sonoran Desert switches from an arthropod-based diet to one that includes cactus nectar during spring when columnar cacti bloom. Such cactophily is a common strategy among nectar-feeding phyllostomid bats, including migratory Leptonycteris species that consume nectar and fruit from columnar cacti. Spring nectarivory by A. pallidus begs the question of whether they also consume cactus fruit during the summer, despite lacking morphological and physiological adaptations for frugivory. We recorded foraging behavior of bats at 134 fruits of the cardón cactus (Pachycereus pringlei) in Baja California Sur, Mexico, and used stable isotope analysis to quantify incorporation of fruit into the summer diet of A. pallidus. We found that A. pallidus visited cardón fruits just as frequently as the lesser long-nosed bat, Leptonycteris yerbabuenae (51.0% and 49.0% of total observed visits, respectively), and removed the same amount of fruit (t59 = –0.85, P = 0.40). Carbon isotopes in wing tissue (n = 37) and exhaled breath (n = 35) of A. pallidus were consistent with frugivory, although variability in the proportion of cactus-derived δ13C in A. pallidus was higher in summer than in spring. Our results confirm that nectarivory in A. pallidus extends to frugivory, highlighting remarkable dietary plasticity in a temperate bat. Moreover, these data suggest that A. pallidus may be an important mutualist to columnar cacti in parts of the Sonoran Desert.