Peter D. Smallwood

Caching decisions by grey squirrels : a test of the handling time and perishability hypotheses

Abstract This study was designed to investigate the relative effects of seed perishability and handling time on the caching preferences of grey squirrels,Sciurus carolinensis, and to test the predictions for caching behaviour that follow from these two hypotheses. Free-ranging squirrels were presented with acorns from two oak subgenera,ErythrobalanusandLeucobalanus, that vary in perishability (due to germination schedules) and handling time (due to acorn size). In six separate caching experiments, individual squirrels were sequentially presented with two acorn types, so that each paired treatment varied in handling time and/or perishability. Caching responses were recorded for each acorn, along with eating and caching times. Squirrels consistently consumed acorns of high perishability and cached acorns of low perishability, without regard to handling time. This result suggests that the perishability of seeds exerts a greater influence than handling time on the grey squirrels decision to cache acorns.

Grey Squirrel Food Preferences: The Effects of Tannin and Fat Concentration

Both tannin and fat concentration in acorns have been postulated to affect squirrel preferences and foraging strategy. Our study directly tests the effects of tannin and fat on the food preferences of free—ranging squirrels (Sciurus carolinensis). Using food items processed from white oak (Quercus alba) acorns with various amounts of tannin and fat added, we find that added tannin significantly reduces the probability that a food item will be eaten and the length of time spent eating it. The addition of fat is shown to attenuate the effects of tannin, but the overall effect is that squirrels do not forage in a manner that maximizes daily energy intake. These results are contrary to the findings of previous studies. A hypothesis to presented to account for the apparent contradiction: The squirrels may maximize energy intake over the entire fall/winter season rather than over a shorter period, such as each foraging bout or day.

CACHE MANAGEMENT BY SMALL MAMMALS: EXPERIMENTAL EVIDENCE FOR THE SIGNIFICANCE OF ACORN-EMBRYO EXCISION

Abstract We conducted 2 field experiments to assess relative importance of acorn-embryo excision in the caching decisions of small mammals. In the 1st, we selectively provisioned small mammals with metal-tagged acorns of red oak (Quercus rubra) and white oak (Q. alba) at 40 point locations in 8 sites in an oak forest in northeastern Pennsylvania. We then followed the fate of cached seeds by relocating acorns with metal detectors soon after they were cached and again in spring after seeds began to germinate. At least 1 species of small mammal excised embryos of >70% of the cached acorns of white oak and <4% of those of red oak. Animals also were observed to revisit caches in spring and excise embryos of germinating acorns. More excised acorns of white oak were found intact in spring than those of red oak, indicating that the behavior is important for long-term storage of these seeds. In a 2nd experiment, we presented free-ranging Mexican gray squirrels (Sciurus aureogaster) with pairs of acorns of 5 native white oak and 5 native red oak species and recorded caching events and whether or not cached seeds had their embryos removed. Squirrels cached significantly more acorns of white oak species, frequently excised embryos of these seeds, and only excised embryos of red oaks when they were germinating. These results support our previous hypothesis that the behavior of embryo excision is geographically widespread and has important implications for cache-management strategies of some diurnal tree squirrels and their effect on dispersal of oaks.

The innate basis of food-hoarding decisions in grey squirrels: evidence for behavioural adaptations to the oaks

Rodents selectively cache acorns of red oak species (subgenus Erythrobalanus; RO) over those of white oaks (subgenus Quercus; WO) because of perishability of early-germinating WO acorns. On occasion, at least three species of tree squirrels also will cache white oak acorns, but only after they excise acorn embryos, thereby preventing germination. Failure to observe embryo excision of acorns in several other mammal species led us to hypothesize that tree squirrels may have an innate tendency to perform embryo excision and possibly the differential caching of RO and WO acorns. To test this, we evaluated the hoarding decisions of eight captive-reared (naive) eastern grey squirrels, Sciurus carolinensis, with no previous experience with acorns and four wild-caught squirrels. Squirrels were presented individually with pairs of dormant RO and nondormant WO acorns (two species) and pairs of dormant and nondormant RO acorns over a 2-month period. Both naive and wild-caught squirrels selectively cached dormant RO acorns more often than those of one WO species (Quercus alba), but showed a much weaker response to other pairs of dormant and nondormant acorns. Naive squirrels also removed the radicles of germinating acorns, and on occasion, attempted to excise embryos of germinating acorns. We conclude that there is a strong innate basis for some of the hoarding decisions made by tree squirrels, strengthening an emerging argument that tree squirrels show specific behavioural adaptations to the oaks.

Seasonal shifts in sex ratios of fledgling American kestrels (Falco sparverius paulus): The Early Bird Hypothesis

We document a seasonal shift in the sex ratios of broods produced by resident southeastern American kestrels (Falco sparverius paulus) breeding in nest boxes in Florida. Early in the breeding season, most biased broods were biased towards males, whereas later in the season, most biased broods were biased towards females. Computer-simulated broods subjected to sex-biased egg and/or nestling mortality demonstrate that it is possible that differential mortality produced the pattern of bias that we observed. However, these simulations do not exclude the possibility that female kestrels were manipulating the primary sex ratio of the broods. We present evidence that this sex ratio shift is adaptive: for males we detected breeding as yearlings, all had fledged early the previous season. No such relationship between season and the probability of breeding as a yearling was found for females. We propose the Early Bird Hypothesis as the ecological basis for the advantage of fledg ing early in males. We hypothesize that pre-emptive competition among post-fledging, dispersing males for breeding sites confers an advantage to males fledged early in the season. This hypothesis may explain why a non-migratory population of the Eurasian kestrel (F. tinnunculus) and non-migratory American kestrels breeding in Florida (F. s. paulus) exhibit this seasonal shift in sex ratios, whereas migratory American kestrels (F. s. sparverius) breeding in Saskatchewan, Canada, do not. We discuss the relevance of the Early Bird Hypothesis for other animal species.

Cache protection strategies of a scatter-hoarding rodent: do tree squirrels engage in behavioural deception?

Behavioural deception has been studied experimentally primarily in captive-raised primates and corvids, and only in a laboratory setting. Here we show that free-living eastern grey squirrels, Sciurus carolinensis, caching food in the presence of conspecifics perform behavioural deception by covering additional empty sites where nothing has been cached. Such deceptive caching (1) occurred in two distinct populations, (2) occurred more often in the close presence of conspecifics and (3) reduced the probability of cache pilferage by surrogate (human) cache pilferers. In an additional experiment, in which we attempted to elicit deceptive behaviour by pilfering caches, deceptive caching appeared as one behaviour in a suite of pilferage-avoidance responses. To our knowledge, this is the first study to show evidence of behavioural deception by a rodent, and the first to use an experimental approach to studying deceptive behaviour in the wild.

WEB-SITE TENURE IN THE LONG-JAWED SPIDER: IS IT RISK-SENSITIVE FORAGING, OR CONSPECIFIC INTERACTIONS?'

Long-jawed spiders (Tetragnatha elongata) present a paradox to behavioral ecologists, because spiders in prey-rich habitats move to new web sites almost every night, while those in poor habitats rebuild their webs on precisely the same spot for many nights in a row. Caraco and Gillespie built a risk-sensitive foraging model to explain this paradox. Their model demonstrates that it may be advantageous to relocate more often when ex- periencing high prey capture rates (under certain regimes of spatiotemporal heterogeneity). However, their model had not been tested. I tested the Caraco-Gillespie model by con- ducting food addition experiments in the field with spiders in the poor habitat. The results do not support the model. A reexamination of the Caraco-Gillespie model suggests that it implicitly assumes unlikely larger scale patterns in prey availability. I present an alternative hypothesis to explain the paradox. Since nonspecific density is higher in rich habitats, I propose that more intense nonspecific interactions in rich habitats cause these spiders to move to new web sites more often. I conducted three replicates of a density reduction experiment in a rich habitat, and the results support the nonspecific density hypothesis. The results of these experiments challenge a widely cited example of risk-sensitive foraging, and underline the importance of explicitly considering multiple scales of variation in ecology.

Wildlife Conservation…in Afghanistan?

The reaction we get whenever we speak about our conservation work in Afghanistan is the same: “Wildlife conservation in Afghanistan?” At first, the idea strikes people as strange, perhaps even preposterous. The common perception of Afghanistan is that of a depauperate landscape, largely devoid of wildlife worth saving. And given the many challenges facing Afghanistan, isn’t conservation a distraction from develop civil society and sustainable economic opportunities. Afghanistan is but one example of this trend.

The Risks of Greening in the Red Zone: Creating Afghanistan’s First National Park in the Midst of Conflict

After two generations of peace, Afghanistan slid into conflict in 1978, turning much of the country into a dangerous red zone. In the midst of this conflict, Afghanistan established its first National Park, Band-e-Amir, to better preserve one of its natural wonders. While such an endeavor may seem frivolous, the environmental planning required to establish the park provided important opportunities for peacebuilding. It set a clear precedent for the involvement of local people in managing their own resources, and led to the central government recognizing and working with a local, democratic institution established to plan and manage Band-e-Amir. It empowered the local people, an ethnic group severely persecuted under previous regimes.

Effects of urbanization on the population structure of freshwater turtles across the United States: Urbanization Effects on Turtles

Landscape-scale alterations that accompany urbanization may negatively affect the population structure of wildlife species such as freshwater turtles. Changes to nesting sites and higher mortality rates due to vehicular collisions and increased predator populations may particularly affect immature turtles and mature female turtles. We hypothesized that the proportions of adult female and immature turtles in a population will negatively correlate with landscape urbanization. As a collaborative effort of the Ecological Research as Education Network (EREN), we sampled freshwater turtle populations in 11 states across the central and eastern United States. Contrary to expectations, we found a significant positive relationship between proportions of mature female painted turtles (Chrysemys picta) and urbanization. We did not detect a relationship between urbanization and proportions of immature turtles. Urbanization may alter the thermal environment of nesting sites such that more females are produced as urbanization increases. Our approach of creating a collaborative network of scientists and students at undergraduate institutions proved valuable in terms of testing our hypothesis over a large spatial scale while also allowing students to gain hands-on experience in conservation science.