Acrobatic squirrels learn to leap and land on tree branches without falling

Arboreal animals often leap through complex canopies to travel and avoid predators. Their success at making split-second, potentially life-threatening decisions of biomechanical capability depends on their skillful use of acrobatic maneuvers and learning from past efforts. Here, we found that free-ranging fox squirrels (Sciurus niger) leaping across unfamiliar, simulated branches decided where to launch by balancing a trade-off between gap distance and branch-bending compliance. Squirrels quickly learned to modify impulse generation upon repeated leaps from unfamiliar, compliant beams. A repertoire of agile landing maneuvers enabled targeted leaping without falling. Unanticipated adaptive landing and leaping “parkour” behavior revealed an innovative solution for particularly challenging leaps. Squirrels deciding and learning how to launch and land demonstrates the synergistic roles of biomechanics and cognition in robust gap-crossing strategies.

Survey of peridomestic mammal susceptibility to SARS-CoV-2 infection

Wild animals have been implicated as the origin of SARS-CoV-2, but it is largely unknown how the virus affects most wildlife species and if wildlife could ultimately serve as a reservoir for maintaining the virus outside the human population. Here we show that several common peridomestic species, including deer mice, bushy-tailed woodrats, and striped skunks, are susceptible to infection and can shed the virus in respiratory secretions. In contrast, we demonstrate that cottontail rabbits, fox squirrels, Wyoming ground squirrels, black-tailed prairie dogs, house mice, and racoons are not susceptible to SARS-CoV-2 infection. Our work expands upon the existing knowledge base of susceptible species and provides evidence that human-wildlife interactions could result in continued transmission of SARS-CoV-2.

Urban fox squirrels exhibit habituation to humans but respond to stimuli from natural predators

Animals in urban areas that experience frequent exposure to humans often behave differently than those in less urban areas, such as less vigilance or anti-predator behavior. These behavioral shifts may be an adaptive response to urbanization and caused by habituation to humans. A possible negative consequence is cross-habituation to natural predators where urban animals exhibit reduced anti-predator behavior in the presence of humans but also to their natural predators. We tested the hypothesis that habituation to humans in urban populations of fox squirrels (Sciurus niger) causes cross-habituation to stimuli from two possible predators (hawks and domestic dogs). We exposed squirrels in multiple urban and less urban sites to acoustic playbacks of a control stimulus (non-predatory bird calls), a natural predator (hawk), and dogs and recorded their vigilance and three different anti-predator behaviors when a human approached them while either broadcasting one of these three playbacks or no playbacks at all. In trials with no playbacks, urban squirrels exhibited reduced vigilance and anti-predator behavior compared to those in less urban areas but there was little evidence that urbanization altered the correlations among the different behaviors we quantified. Urban squirrels exhibited increased vigilance and anti-predator behavior when exposed to a human paired with hawk playbacks compared to the control playbacks. This indicates that urban squirrels did perceive and assess risk to the natural predator appropriately despite exhibiting habituation to humans. There is currently little evidence that habituation to humans causes animals to lose their fear of natural predators.

Holocene faunal procurement and species response to climate change in the Ohio River valley

This paper examines the temporal distribution of 163 distinct species recovered from 21 well-dated Holocene age archaeological sites in the Ohio River valley to determine patterns of faunal resource procurement and their response to periods of climate change. Climate change proxies include bison, long-billed curlew, pine marten, porcupine, prairie vole, and swamp rabbit. While the rice rat may be a proxy of climate change, its initial appearance in the Archaic cultural period co-occurs with storable starchy and oily seed crops such as erect knotweed, little barley, marsh elder, maygrass, and sunflower. Subsistence proxies that transcend climate change include variety of aquatic (bass/sunfish, buffalo, channel catfish, freshwater drum, gar, mussels, snails, snapping and spiny softshell turtles, and river redhorse sucker), avian (blue-wing teal, Canada goose, and turkey), and terrestrial species (dog, eastern cotton-tail, elk, gray and fox squirrels, opossum, raccoon, timber rattlesnake, and woodchuck). Caldwell’s Primary Forest Efficiency remains a valid theoretical model of Holocene subsistence strategy in the Ohio River valley.

How squirrels protect their caches: Location, conspicuousness during caching, and proximity to kin influence cache lifespan

Scatter-hoarding animals cannot physically protect individual caches, and instead utilize several behavioral strategies that are hypothesized to offer protection for caches. We validated the use of physically altered, cacheable food items, and determined that intraspecific pilfering among free-ranging fox squirrels (N = 23) could be assessed in the field. In this study we were able to identify specific individual squirrels who pilfered or moved caches that had been stored by a conspecific. We identified a high level of pilfering (25%) among this population. In a subsequent study, we assessed the fate of squirrel-made caches. Nineteen fox squirrels cached 294 hazelnuts with passive integrated transponder tags implanted in them. Variables collected included assessment and cache investment and protection behaviors; cache location, substrate, and conspicuousness of each cache; how long each cache remained in its original location, and the location where the cache was finally consumed. We also examined whether assessment or cache protection behaviors were related to the outcomes of buried nuts. Finally, we measured the population dynamics and heterogeneity of squirrels in this study, testing the hypothesis that cache proximity and pilferage tolerance could serve as a form of kin selection. Polymer chain reaction (PCR) was used to analyze hair samples and determine relatedness among 15 squirrels, and the potential impact of relatedness on caching behavior. Results suggested that cache protection behaviors and the lifespan of a cache were dependent on the conspicuousness of a cache. Squirrels may mitigate some of the costs of pilfering by caching closer to the caches of related squirrels than to those of non-related squirrels.