The overgrown lots and sidewalks of California cities might not seem like a great place to seek out nutritious greens, but in a recent study published in PLOS ONE, Professor Philip Stark and his team
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We’re all familiar with the shell game, though many may not recognize it by that name. Popular with street swindlers and sports fans at halftime, it has been annoying those unable to locate which cup the ball is under—most people—as long as anyone can remember. But, what if you were a small ruminant playing a modified version of the game, in which cups were not moved? Seems easier, right? Turns out it may depend on what kind of ruminant you are.
The authors of a recent PLOS ONE article updated this age-old game to find out whether goats and sheep, given information upfront about which cup the food was (or was not) under, could find the food again once the cups were replaced. The ability to connect an experience with an imagined result (“If I see that the cup is empty, the other must have the food!”) is called inferential reasoning, and has been tested in dogs, primates, and birds. Different levels of inferential reasoning, especially between two closely related species, may be linked to differences in the way they search for and find food. A deeper understanding of the different feeding behaviors found in ruminants could shed light on the evolutionary practices that shape these behaviors and help us understand how domesticated breeds have modified their behavior over time to better fit a farming environment.
In this study, researchers ran two rounds of testing with slightly different protocols to evaluate how the ruminants’ behavior would change in response to varied amounts of information. They created an experimental set with the animal separated by a series of bars from the researcher and a table (see image above) that held two cups, one with a piece of food hidden underneath. In the first test, researchers lifted one of the following:
- both cups (full information)
- the baited cup (direct information – shown in the video below)
- the unbaited cup (indirect information)
- no cups (no information)
The animal then chose a cup and was rewarded with food if found. The video below shows a sheep correctly identifying the baited cup after receiving direct information on the food’s location.
To minimize the possibility that animals would simply select the cup most recently moved by the researcher, the authors further modified the game for the second round of testing. A set of internal cups was added under each external cup, some transparent and some opaque, allowing the researchers to lift both external cups simultaneously while providing the same amount of information to the animals.
Animals participating in the test were again presented with two cups. Both external cups were removed simultaneously to reveal the inner set, which were one of the following:
- both transparent (full information)
- the baited cup transparent and the unbaited one opaque (direct information)
- the baited cup opaque and the unbaited transparent (indirect information)
- both opaque (no information)
In the same way as in the first experiment, animals were given a chance to select a cup and were rewarded with food if found.
When reviewing the results of all the sessions, the authors found that goats were more successful than sheep at identifying the baited cup when given full or direct information, although sheep also chose the baited cup more often under these circumstances. The second experiment showed that goats were also more successful at finding food when provided with indirect information. In both experiments, sheep did not guess better than chance when shown the empty contents of the unbaited cup or no cups at all, and goats did not guess better than chance when neither of the cups were listed.
Though several factors varied between species populations used in this experiment—like the time of day experiments were completed, number of animals tested, or history of testing experience in goats—the authors saw no sign of improved performance due to learning in goats, and no differences in motivation as tests continued.
The researchers speculate that the different foraging behaviors used by goats and sheep allowed goats to get ahead in these experiments. Goats are dietary browsers, meaning they are more selective in what they eat and prefer low-fiber foods, like plant stems and leaves. Sheep, as dietary grazers, feed primarily on high fiber foods like grass, and are not at all particular about what they consume. If goats have evolved to be picky, selective eaters, then it makes sense that they might have a better memory for where they saw food in the past, and the insight to avoid an empty cup when they saw one. Future studies on this topic could provide insight on decision making and risk sensitivity in these animals, and give us a glimpse into the minds of a species that can actually beat the odds in the shell game.
- Squirrels – Nut Sleuths or Just Nuts?
- Using the Aesop’s Fable Paradigm to Investigate Causal Understanding of Water Displacement by New Caledonian Crows
- Chimpanzees Are Extremely Picky About Where They Sleep (read more here)
Citation: Nawroth C, von Borell E, Langbein J (2014) Exclusion Performance in Dwarf Goats (Capra aegagrus hircus) and Sheep (Ovis orientalis aries). PLoS ONE 9(4): e93534. doi:10.1371/journal.pone.0093534
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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.
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
While few question the importance of maternal care in humans, scientists do question the influence of a mother’s behavior in other species. Researchers from the Max Planck Institute for Ornithology have now published an article in PLOS ONE showing exactly how important a mother’s guidance can be to our friend the western lowland gorilla. After monitoring the spread of two specific behaviors in captive groups of gorillas, the authors suggest that gorilla mothers play a vital role in social learning and the transmission of behaviors between generations.
The authors videotaped gorilla behavior for 4-6 hours per day over the course of eight weeks in 2000 and 2010 at Howletts Wild Animal Parks. Throughout their sittings, they watched for two specific behaviors shown by different individuals: the “Puff-Blowing” technique, used during mealtimes to separate oat from chaff, and the “Throw-Kiss-Display,” one male gorilla’s coy way of drawing visitors’ attention to him. Check out the live-action versions in the videos below.
During the initial observational period in 2000, the “Puff-Blowing” technique was used by three adult females, while the “Throw-Kiss-Display” was implemented by a single silverback male, Kouillou, and no other members of the group.
By the time the researchers returned in 2010, the “Puff-Blowing” technique was practiced by 15 individuals, while the “Throw-Kiss-Display” had been dropped entirely, even by the original practitioner.
When the researchers analyzed the data, they found that the spread of the observed “Puff-Blowing” technique to new gorillas could be tracked through mother-child relationships. All but three offspring (13 total) of the original three mothers used the technique. Furthermore, this behavior was never seen in the offspring of mothers who did not perform the technique.
Based on their observations, the authors suggest that the actions of the gorilla mother play a major role in the transmission of behaviors. In other words, baby gorilla see, baby gorilla do. While the authors mention that “Puff-Blowing” may be more likely to be passed down because it’s useful at mealtime—unlike the “Throw-Kiss-Display”—they argue that the path of transmission (mother-offspring) is significant. The authors also indicate that genetic factors may affect the occurrence of these behaviors, as not all offspring of the “Puff-Blowing” mothers inherited the action, suggesting that other forces may be at play.
Lesson learned: Even gorillas need their mommies.
For more evidence of the importance of mothers in the animal kingdom, check out this paper on migration patterns in humpback whales.
Citation: Luef EM, Pika S (2013) Gorilla Mothers Also Matter! New Insights on Social Transmission in Gorillas (Gorilla gorilla gorilla) in Captivity. PLoS ONE 8(11): e79600. doi:10.1371/journal.pone.0079600
Image Credit: USINFO Photo Gallery
Videos: S1 and S2 from the paper