Risk Assessment and Flight Decisions in Adult versus Juvenile Squirrels (Sciurus carolinensis)

One way to quantify a prey’s response to a predator is by flight initiation distance (FID), the distance between a predator and prey at the moment the prey flees. As perceived risk from a predator increases, FID increases. Juvenile animals typically flee from approaching threats sooner than do adults because they have less able risk assessment. However, our observations suggested juvenile squirrels might use a different tactic: foraging near refuges. We first tested whether age affected squirrels’ FID in response to an approaching human on the UofL campus, where squirrels experience high levels of interactions with humans from an early age. We identified a focal squirrel’s age (adult or juvenile), and waited until it was within 5 meters of a refuge, i.e. a tree at least 6 meters tall. For all trials, the approaching person, focal squirrel, and refuge were in a straight line, with the squirrel between the person and the refuge. This arrangement and short distance to refuge facilitated flight decisions. A researcher approached each squirrel at 2 steps/second until the squirrel fled, and then measured initial distance between predator (person) and prey, FID, and the squirrel’s distance to the refuge. Results showed no difference in FID between adults and juveniles (GLM analysis; p \u3e 0.50). We then measured squirrels’ distances from trees while foraging, and we found that juveniles indeed compensated for low FID by by a different anti-predator behavior: foraging significantly closer to the refuge than adults. This is a novel finding among vertebrates.https://ir.library.louisville.edu/uars/1044/thumbnail.jp

Conspecifics and Familiar Odors Alter Movement Patterns in a Land Snail, Cepaea hortensis

In some animals, unfamiliarity with a place and the presence of a conspecific can change movement patterns, often altering individuals’ routes, exploration, and the directions taken. Patterns such as these can affect individual survival, and thus might be present across a wide range of taxa, although mostly vertebrates have been studied. We used a native Kentucky land snail (white-lipped globe snail, Cepaea hortensis) to investigate how snail size, familiarity and the recent presence of a conspecific affect movement of snails in a novel environment. We also tested whether presence of a familiar smell influenced movement on a 25X25 cm2 glass plate. Size, familiarity, and signs of a conspecific all affected movement patterns. For example, small snails delayed longer before moving, paused more, travelled shorter distances, and made more convoluted paths than did large snails. When a familiar odor was present, snails travelled further and made more direct trails. For both large and small snails, the second snail in a trial made longer trails and travelled further from the start than the first snail. The second snail did not trace the path of the first, but did go in the same general direction more frequently than expected by chance. When investigating a novel environment, the snails made surprisingly complex decisions about their route and pattern of movement depending on the presence of a familiar smell or signs of a conspecific. These cues and snail size play a vital role in movement decisions, and may help individuals find sites that increase survivalhttps://ir.library.louisville.edu/uars/1041/thumbnail.jp

Proximate constraints on intruder detection in the dragonfly Perithemis tenera (Odonata: Libellulidae): effects of angle of approach and background

The implications of insects’ vision for territorial defense have been relatively little studied in the field. In the dragonfly Perithemis tenera Say we investigated whether either the angle at which an intruder was viewed by a territorial resident or the background against which it was viewed affected the detection of that intruder. Residents detected intruders at a greater distance if the intruders were directly in front of them; they also detected more intruders in front of them than from other angles. Intruders viewed against distant vegetation were detected more readily than were intruders against near vegetation. Residents detected more intruders viewed against distant vegetation than viewed against near vegetation; however, more intruders than expected were detected against near vegetation. The probability of detecting intruders depends on the angle at which they are viewed and the background behind them. Hence, there may be selection on territorial residents to adjust their orientation and space use to enhance their view of their territory and intruders

Proximate constraints on intruder detection in the dragonfly Perithemis tenera (Odonata: Libellulidae): effects of angle of approach and background

The implications of insects’ vision for territorial defense have been relatively little studied in the field. In the dragonfly Perithemis tenera Say we investigated whether either the angle at which an intruder was viewed by a territorial resident or the background against which it was viewed affected the detection of that intruder. Residents detected intruders at a greater distance if the intruders were directly in front of them; they also detected more intruders in front of them than from other angles. Intruders viewed against distant vegetation were detected more readily than were intruders against near vegetation. Residents detected more intruders viewed against distant vegetation than viewed against near vegetation; however, more intruders than expected were detected against near vegetation. The probability of detecting intruders depends on the angle at which they are viewed and the background behind them. Hence, there may be selection on territorial residents to adjust their orientation and space use to enhance their view of their territory and intruders

Squirrels Do the Math: Flight Trajectories in Eastern Gray Squirrels (Sciurus carolinensis)

Animals are under strong selective pressures to make correct decisions when attempting to escape an approaching predator, and not surprisingly many studies have shown that animals adjust their flight initiation behavior in response to risk. However, we have a poor understanding of animals' capability to select an appropriate flight trajectory. We investigated whether eastern gray squirrels would adjust their flight trajectory based on the relative locations of the squirrel, the approaching threat, and potential refuges. We used a person running toward a focal squirrel (N = 122) as the threat and considered the three trees nearest the squirrel and taller than 8 m to be potential refuges. Squirrels were strongly affected by the angle (θ) formed by the locations of person, squirrel, and the three nearest trees. A squirrel was less likely to run to the nearest tree (Tree 1) when θ1 was relatively acute, but also less likely to run to Tree 1 when θ2 was obtuse, making Tree 2 a more attractive refuge. A squirrel was more likely to run to Tree 1 if it was close and if Tree 2 was relatively far. Subtle differences in the effects of θ1 vs. θ2 on squirrel refuge choice support the idea that squirrels prefer a nearby refuge. Squirrels were more likely to select Trees 2 and 3 rather than Tree 1 only when θ2 was obtuse (105°). In contrast, most squirrels chose to run to Tree 1 when θ1 was >65°; thus squirrels were more likely to choose Tree 1 even when doing so required running at least partly toward the approaching threat. The decisions made by focal squirrels provide evidence that this species' assessment of risk is highly nuanced. A great deal of variation has been reported in responses to predators within species. While part of the variation may be due to strategic unpredictability on the part of the prey, part of it may also be due to differences in flight trajectory and refuge preferences that have not been well-studied

The effect of habitat structure and visibility on territory shape and space use : theoretical and empirical studies.

Degree granted in Zoology.Typescript.SPEC. COLL. HAS ARCHIVAL COPY; MICRO. ROOM HAS MICROFICHE COPY (2 SHEETS).Thesis (Ph.D.)--U. of Calif., Davis.Mode of access: Internet

Proximate constraints on intruder detection in the dragonfly Perithemis tenera (Odonata: Libellulidae): effects of angle of approach and background

The implications of insects’ vision for territorial defense have been relatively little studied in the field. In the dragonfly Perithemis tenera Say we investigated whether either the angle at which an intruder was viewed by a territorial resident or the background against which it was viewed affected the detection of that intruder. Residents detected intruders at a greater distance if the intruders were directly in front of them; they also detected more intruders in front of them than from other angles. Intruders viewed against distant vegetation were detected more readily than were intruders against near vegetation. Residents detected more intruders viewed against distant vegetation than viewed against near vegetation; however, more intruders than expected were detected against near vegetation. The probability of detecting intruders depends on the angle at which they are viewed and the background behind them. Hence, there may be selection on territorial residents to adjust their orientation and space use to enhance their view of their territory and intruders