Squirrels – Nut Sleuths or Just Nuts?

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Crazed squirrels: we’ve all seen them. Some dashing toward you only to stop short long enough to glare with beady eyes before fleeing, others dive-bombing the dirt, coming up with their heads waving back and forth. They’re the butt of many a joke on college campuses, providing endless amusement with their antics. Some UC Berkeley students even think that the resident campus squirrels may have gobbled up substances left over from the wilder moments of Berkeley’s past, leaving them permanently crazed. However, according to a recently published PLOS ONE article from UC Berkeley, these squirrels’ seemingly odd behavior may actually have a purpose. We’ve long known that scatter-hoarders will store food they find to prepare for periods when it’s less abundant, but there is little information on the hoarding process. Turns out these squirrels might actually have a refined evaluation method based on economic variables like food availability and season. To eat now, or cache for later?

Researchers interacted with 23 fox squirrels, a species well-habituated to humans, in two sessions during the summer and fall of 2010 on the Berkeley campus, evaluating food collection behavior during both lean (summer) and bountiful (fall) seasons. The authors engaged the squirrels with calls and gestures to attract their attention, and the first squirrel to approach was the focus of that round of testing.

Each squirrel was given a series of 15 nuts, either peanuts or hazelnuts, in one of two sequences. Some were offered five peanuts, followed by five hazelnuts, then five more peanuts (PHP). Others were given five hazelnuts, five peanuts, then five hazelnuts (HPH). The purpose of this variation was to evaluate how squirrels would respond to offers of nuts with different nutritional and “economic” values at different times. Hazelnuts are, on average, larger than peanuts, and their hard shell prevents spoiling when stored long term, but peanuts tend to have more calories and protein per nut.  Researchers videotaped and coded each encounter to calculate variables, like the number of head flicks per nut, time spent pawing a nut, and time spent traveling or caching nuts. See the video below for a visual example of these behaviors.

https://www.youtube.com/watch?v=MKKgpZoZ0Y0&feature=youtu.be

The results showed that season and nut type significantly affected the squirrel’s response, and the squirrel’s evaluation of the nut could forecast its course of action. Predictably, the fall trial showed squirrels quickly caching most of their nuts, likely taking advantage of the season’s abundance. Squirrels ate more nuts in the summer, though they still cached the majority of hazelnuts (76% vs. 99% cached in the fall) likely due to their longer “shelf life”.

The squirrels who head-flicked at least one time in response to a nut cached it nearly 70% of the time, while those who spent more time pawing the nut tended to eat it (perhaps searching for the perfect point of entry?). The time spent caching and likelihood of head flicking were clearly linked to the type of nut received and to the trial number, with time spent evaluating a nut decreasing as the trials continued for a squirrel. The authors suggest that the changes in food assessment strategies in response to resource availability provide an example of flexible economic decision making in a nonhuman species.

So, now that squirrels are possibly making economically prudent decisions when evaluating nuts, I guess we have to give them a break when we see them running around like crazy on campus. Doesn’t mean we’ll stop laughing.

Citation: Delgado MM, Nicholas M, Petrie DJ, Jacobs LF (2014) Fox Squirrels Match Food Assessment and Cache Effort to Value and Scarcity. PLoS ONE 9(3):e92892. doi:10.1371/journal.pone.0092892

Image: Squirrel by likeaduck

Video: Video S1 from the article

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Unlikely Critters Found in Avocado Orchards

journal.pone.0068025.g002Wildlife isn’t always restricted to wild spaces.

Avocado orchards and other agricultural landscapes also buzz with species that forage and reproduce in these spaces. Birds and herbivores are able to find food and shelter in these cultivated areas, but what about carnivores?  In a study published this week in PLOS ONE, researchers at the University of Washington have discovered that mammalian carnivores also occupy avocado orchards in southern California.

The authors used motion-activated cameras to observe animals in orchards and in adjacent wild lands in Santa Barbara and Ventura.  Avocado orchards were of particular interest due to their location near native vegetation.

Through their investigation, the researchers detected more carnivores in the avocado orchards than in neighboring wild land sites. At least 7 out of the 11 native carnivores in the area were spotted roaming the orchards, including coyotes, gray foxes and bobcats.3561367265_093313316f

Having delicious avocados handy may explain why some omnivores such as bears and raccoons are present in the area, however, little is known about why animals like bobcats and mountain lions might leave their wild habitat for cultivated land. One possibility is that the orchards provide water and fruits for herbivores, and an increased herbivore population could translate to more prey for the carnivores. The orchards may also serve as shelter, offering forest cover similar to oak woodlands in the area.

These native species cannot always persist in protected reserves, so it is important to learn how cultivated lands can serve their lifestyle and behaviors. The carnivores may not be searching for the perfect guacamole ingredient; however there is no doubt that the avocado orchards are serving as a habitat for a wide range of species.

Citation: Nogeire TM, Davis FW, Duggan JM, Crooks KR, Boydston EE (2013) Carnivore Use of Avocado Orchards across an Agricultural-Wildland Gradient. PLoS ONE 8(7): e68025. doi:10.1371/journal.pone.0068025

Image 1: doi:10.1371/journal.pone.0068025

Image 2: Image on Flickr by Graeme Churchard

Sharing was Caring for Ancient Humans and Their Prehistoric Pups

huskies_1While the tale of how man’s best friend came to be (i.e., domestication) is still slowly unfolding, a recently published study in PLOS ONE may provide a little context—or justification?—for dog lovers everywhere. It turns out that even thousands of years ago, humans loved to share food with, play with, and dress up their furry friends.

In the study titled “Burying Dogs in Ancient Cis-Baikal, Siberia: Temporal Trends and Relationships with Human Diet and Subsistence Practices,” biologists, anthropologists, and archaeologists joined forces to investigate the nature of the ancient human-dog relationship by analyzing previously excavated canid remains worldwide, with a large portion of specimens in modern-day Eastern Siberia, Russia. The authors performed genetic analysis and skull comparisons to establish that the canid specimens were most likely dogs, not wolves, which was an unsurprising but important distinction when investigating the human-canine bond. The canid skulls from the Cis-Baikal region most closely resembled large Siberian huskies, or sled dogs. Radiocarbon dating from previous studies also provided information regarding the dates of death and other contextual information at the burial sites.

The researchers found that the dogs buried in Siberia, many during the Early Neolithic period 7,000-8,000 years ago, were only found at burial sites shared with foraging humans. Dogs were found buried in resting positions, or immediately next to humans at these sites, and their graves often included various items or tools seemingly meant for the dogs. One dog in particular was adorned with a red deer tooth necklace around its neck and deer remnants by its side, and another was buried with what appears to be a pebble or toy in its mouth.

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By analyzing the carbon and nitrogen in human and dog specimens in this region, the researchers were able to determine similarities in human and dog diets, both of which were rich in fish. This finding may be somewhat surprising because one might assume that dogs helped humans hunt terrestrial game, and would consequently be less likely found among humans that ate primarily fish.

The authors speculate that dogs were considered spiritually similar to humans, and were therefore buried at the same time in the same graves. The nature of the burials and the similarities in diet also point toward an intimate and personal relationship, both emotional and social, between humans and their dogs—one that involved sharing food and giving dogs the same burial rites as the humans they lived among. Ancient dogs weren’t just work animals or hunters, the authors suggest, but important companion animals and friends as well.

Citation: Losey RJ, Garvie-Lok S, Leonard JA, Katzenberg MA, Germonpré M, et al. (2013) Burying Dogs in Ancient Cis-Baikal, Siberia: Temporal Trends and Relationships with Human Diet and Subsistence Practices. PLoS ONE 8(5): e63740. doi:10.1371/journal.pone.0063740

Image Credits: Losey RJ, Garvie-Lok S, Leonard JA, Katzenberg MA, Germonpré M, et al. (2013) Burying Dogs in Ancient Cis-Baikal, Siberia: Temporal Trends and Relationships with Human Diet and Subsistence Practices. PLoS ONE 8(5): e63740. doi:10.1371/journal.pone.0063740

Siberian husky photo by Pixel Spit