FORAGING BEHAVIOR OF SQUIRRELS

Foraging Behavior of Squirrels

Foraging Behavior of Squirrels

Introduction

Behavioural ecology encompasses a whole spectrum of research topics (Krebs & Davies 1993). A recurring debate surrounds one area of this discipline; theories of resource utilization e.g. optimal foraging (Stephens & Krebs 1986). The optimal foraging theory was first proposed by MacArthur & Pianka (1966) in which they state; “The basic procedure for determining optimal utilization of time or energy budgets is very simple: an activity should be enlarged as long as the resulting gain in time spent per unit foods exceeds the loss”. Although simple, this theory provides an underlay for the more complex science of foraging ecology. Furthermore, this theory has been extensively tested in both theoretical (e.g. MacArthur & Pianka 1966; Stephens & Krebs 1986) and empirical scenarios (e.g. Greico 2001). This study concentrates on the latter but considers the premise behind the theory as a rationale to the hypotheses tested. In addition to this theory, this study tested how a number of manipulated scenarios can sculpt 'optimal foraging' through the use of predator cues and a variation in distance of reward. I rigorously tested foraging through diet choice experiments using the Grey squirrel (Sciurus carolinensis) as the model organism.

Previous studies examining optimal foraging in S. carolinensis have predominately looked at quantifying diet choice from non-manipulated field experiments (Lewis 1982) or through manipulations of a single food item (Lima 1985). No studies have however considered optimal foraging in S. carolinensis using manipulated field experiments with a range (in both energy and handling times) of food items. Nonetheless, there is a wealth of research considering the potential consequences of predation-foraging effects on optimality (e.g. Lima et al. 1985; Lima & Valone 1986). These studies have shown how in response to potential predators diet choice and/or foraging efficiency can shift to minimize the risk of predation whilst incurring little energetic costs.

Background

When conducting behavioural ecology research, various postulations must be made in order for a justification of both methods and assumptions. This section will concentrate on describing the theory behind foraging behaviours and energy needs. A requirement of every living thing is that a daily energy level must be reached in order to ensure survival. This level is reached through acquisition of energy whether it be directly from photons from solar energy or from food that they consume. Petrusewicz (1967) coined the term 'daily energy budget' from which he produced a theoretical equation to describe the energy dynamics of an individual or group:

C = A + (FU),

A = R + P

Where, C = energy consumed daily as food, A = energy assimilated into the body, FU = energy lost from the body as faeces or urine, R = energy utilized in metabolic processes and P = energy incorporated into body tissues. This fundamental equation provides the basis for a whole spectrum of research on optimal foraging and energy gain.

In order to achieve this energy quota an individual must often make 'conscious decisions' on its foraging tactics whereby energy ...