ESRM 351 Wildlife Survey Methods & Study Design

Vocabulary terms and mathematical formulas covering wildlife survey methods including line transects, double observer point counts, and study design principles from ESRM 351.

Line transect survey

A distance survey method where the observer travels a transect of length $L$ and records perpendicular distances of animals seen within a specific width ($w$) on either side of the line.

Detection probability ($p$)

In line transect surveys, a computer-estimated value representing the probability of detecting an individual as a function of its distance from the transect line.

Line transect density formula

The equation used to calculate animal density: $D = \frac{n}{2pwL}$, where $n$ is the number of animals recorded.

Internal validity

The extent to which differences between treatments can be attributed to the treatment itself; it can be lowered by the lack of interspersion or bias during laboratory analysis.

Pseudoreplication

A study design error where multiple observations are treated as independent replicates when they are actually non-independent, such as multiple locations from the same individual or individuals within the same herd.

External validity

The extent to which study findings can be generalized, often limited by low replication or a narrow scope of inference (e.g., sampling during only one season).

Interspersion

The practice of alternating or randomizing the timing and location of sampling across different treatment sites to avoid confounding factors.

Independent double observer method

A point count technique used to estimate bird density where two observers independently record observations and use a mark-recapture equation to account for individuals missed.

Chapman modification of Lincoln-Peterson equation

The formula used in double observer methods to estimate the number of birds per plot: $\hat{N} = \frac{(n_1+1)(n_2+1)}{m_2+1} - 1$.

Sub-plots

Observation units within a larger survey site (e.g., plots within a forest stand) that are not independent of one another and should be averaged before statistical analysis.

Powderboard track index method

A sampling technique used to monitor changes in animal abundance, such as Uinta ground squirrels, by recording track density on specific plots.

Sample size estimation formula

The equation to determine the number of plots needed for a desired level of accuracy and precision: $n = \frac{s^2 t^2}{ME^2}$, where $s$ is standard deviation, $t$ is the critical value, and $ME$ is the margin of error.

Precision

The closeness of measurements to each other, often expressed in study goals as a percentage of the true mean (e.g., within $10\%$) for a specific confidence interval.

Accuracy

The closeness of a measurement to its true value, which can be compromised by observer inexperience or bias during the classification of specimens.

Scope of inference

The breadth of conclusions that can be made from a study, which is restricted when factors like non-random plot placement or limited temporal duration are present.