Home-Range Security

A Fresh Look at Foraging and Anti-Predation Behavior in Eastern Grey Squirrels

Noah Sager18 November 2010Chicago State UniversityDepartment of Geography

The Field

Behavioral Ecology The study of an animal’s behavior (decisions) dependent

upon its environment, and the conferred adaptive benefits or costs

Behavioral Geography The study of a human’s behavior (decisions) dependent

upon its environment, and the conferred adaptive benefits or costs

Why Psychoanalyze Animals?

“True” Science

Applications

Correlationshttp://www.cartoonstock.com/lowres/sma0070l.jpg

The Eastern Grey Squirrel

(Sciurus carolinensis)

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Small (~400g)Scatter-hoardingDiurnalSpatial MemoryNestsIntermittent Locomotion

Definitions

Anti-Predator Vigilance ‘Early-warning’ behavior that enables animals to avoid predation

(e.g. predator detection)

Intermittent Locomotion Cyclical movement of motion, pause (vigilance), motion

Foraging The gathering and subsequent consumption or scatter-hoarding of

food items

Scatter-hoarding The burying or hoarding of food items in individual locations

Pause Postures

Left to RightExtended UprightUprightSemi-UprightQuadrupedal Up*Quadrupedal Down*Tripedal*

Previous Studies

Wistrand (1974)Newman et al. (1988)Jones (1998)McAdam & Kramer (1998)Tchabovsky et al. (2001) Trouilloud et al. (2004)

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Anti-Predator Vigilance:Feed or Flee?

Study Area Urban parks around Montreal, Quebec (Canada) Summer of 2004

Description The non-invasive video recording of squirrel behavior at artificial

foraging patches with varying distances from cover

Materials digital video camera, food dish, measuring tape, sand, stakes peanuts, peanut butter, sunflower seeds

Anti-Predator Vigilance:Food or Foe?

Methods 36 squirrels (1 per site) 100m distance between sites 3 distances from cover (0.3m, 5m and 15m)

Newman et al. (1988) Food patch: 1 liter ‘treated’ sand patch with inverted food dish

25 whole sunflower seeds (15 buried), 1/4 tsp. creamy peanut butter, 5 whole peanuts

Confounding conspecifics End of trial requirements

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Anti-Predator Vigilance:Forage or Die Trying

Data Extraction Noldus Observer

Digital recordings analyzed frame-by-frame Behavior Durations and Frequency

Locomotion Pauses

Transition Times Motion to Pause (locomotion to vigilance) Pause to Pause (pause posture to posture) Pause to Motion (vigilance to locomotion)

Anti-Predator Vigilance:It’s a Dog Eat Squirrel World

Data Analysis One and two-way ANOVAs (analysis of variance) Bonferroni corrections (post-hoc)

Question 1: Are more upright (more vigilant) pause postures really more costly?

Question 2: Are transition durations dependent upon pause posture?

Question 3: Is there an effect of distance from cover on pause duration or transition times?

Question 4: Is there a vigilance component to foraging?

Results

Pause durations varied significantly depending upon posture, with upright pauses lasting longer than semi-upright pauses (F2,52=8.657, P<0.01), and semi-upright pauses lasting longer than quadrupedal pauses

(F2,46=3.115, P<0.01), and this was still significant following a Bonferroni post-hoc test.

Results

Posture type had a significant effect on transition times, requiring more time for a squirrel to move from locomotion to a semi-upright posture than to a quadrupedal posture (F2,52=49.396, P<0.01) and more time

to move to locomotion from a semi-upright posture than from a quadrupedal posture (F2,66=68.910, P<0.01), and this was still significant following a Bonferroni post-hoc test.

Results

There was a slight effect of distance on transition times to move from locomotion to quadrupedal alert (F2,44=0.067, P=0.057), but no effect from locomotion to semi-upright alert posture (F2,42=0.270, P=0.758). Accordingly,

there was no effect of distance on transition times moving from quadrupedal alert to locomotion (F2,58=0.065, P=0.352), to semi-upright alert (F2,32=0.351, P=0.707), or from semi-upright alert to locomotion (F2,49=0.600,

P=0.553). There was no effect of distance from cover on pause duration for all postures (F3,31=0.902, P=0.409).

Results

Left: Frequency Distribution of Quadrupedal Pauses During Locomotion. Duration category is measured by number of frames (1 Frame = 1/30 seconds). n = 624, mean = 3.92, median = 8.

Right : Frequency Distribution of Quadrupedal Pauses In Patch. Duration category is measured by number of frames (1 Frame = 1/30 seconds). n = 164, mean = 14.37, median = 7.

(see: Makowska & Kramer 2007)

Discussion

Question 1: Are more upright (more vigilant) pause postures really more costly? Supported (first empirical evidence)

Question 2: Are transition durations dependent upon pause posture? Supported (first empirical evidence)

Question 3: Is there an effect of distance from cover on pause duration or transition times? Failed to support (contrary to previous studies)

Question 4: Is there a vigilance component to foraging? Failed to support (requires future studies)

Conclusion(s)

Vigilance is costly Positive correlation between pause duration and posture,

and between transition time and posture

Constrained decisions, time-budget Squirrels maintain a constant time-budget concerning

foraging and anti-predation activities

Vigilance trade-offs Distance from Cover versus Detection Range*

Acknowledgements

McGill University - Behavioural Ecology Lab 2004 - 2005

Dr. Donald L. Kramer Research Supervisor

Talya Hackett Field Assistant

The Squirrels Numbers 1 - ?

Questions or Comments?

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