3.3 Presence/Not Detected (Possible)

Recommended method: A combination of simple point counts along an encounter transect.

A combination of unlimited radius point counts with connecting encounter transects will maximize species detection. Thus data are collected at point count stations and while travelling between stations (provided that you travel by foot).

3.3.1 Simple Point Counts along an Encounter Transect

Office procedures

• Review the introductory manual No.1, Species Inventory Fundamentals.
• Obtain maps for Project and Study Area(s) (e.g., 1:5,000 air photo maps, 1:20 000 forest cover maps, 1:20 000 TRIM maps, 1:50 000 NTS topographic maps). Any map which is used to record data should be referenced to NAD83.
• Outline the Project Area on a small to large scale map (1:250,000 - 1:20,000).
• Determine Biogeoclimatic zones and subzones, Ecoregion, Ecosection, and Broad Ecosystem Units for the Project area from maps.
• Delineate one to many Study Areas within this Project Area. Study areas should be representative of the Project Area if conclusions are to be made about the Project Area. For example, this means if a system of stratification is used in the Sampling Design then strata within the Study Areas should represent relevant strata in the larger Project Area.
• Based on the maps and other knowledge of the Study Area (previous reports, local resource specialists) identify strata which are of most interest for surveying.
• Compile a list which includes all potential songbirds for the Study Area.

Sampling design

• Stratify habitat according to objectives.
• Systematically sample within strata using transects and point counts with unlimited radius. [The Design Components for this survey are transects and point count stations.]
• When possible, randomize or change observers between transects / stations to minimize recurring bias in any segment of a survey.

Sampling effort

• To assess whether enough effort was spent in an area to determine presence/not detected, graph the number of species versus the number of point counts, and/or distance travelled along the transect. When the graph reaches an asymptote (levels off), it can be assumed that most of the species have been detected. A graph of species detected as a function of point counts or distance travelled will approximate optimal search effort to detect species. However, these results will only be applicable to the season, and area in which the survey was conducted. Other factors such as weather, observer, and habitat types will also affect the number of species detected. Therefore optimal sample effort should be determined on a study specific basis. For individual species it is possible to calculate optimal effort using the negative binomial distribution as detailed in manual No. 1, Species Inventory Fundamentals.

Personnel

• The crew leader should be a qualified biologist with experience in encounter transects and simple point count methods.
• Field crew must be competent in identifying birds by sight and song.

Equipment

• Maps
• GPS (use NAD83)
• Compass
• Hip chain (Remember to gather all the string between stations; failure to do so can result in the death of many birds)
• Measuring tape
• Flagging tape
• Binoculars
• Data forms
• Clipboard
• Tape recorder for field if desire
• Digital watch
• Thermometer
• Field guide(s) for species confirmation
• Bird song tapes for training

Field procedures

• Record transect and point count station information and observations on the dataform: Animal Observation Form - Songbird Encounter Transect & Simple Point Counts.
• Use the standard five letter species code (class code and the first two letters of each word e.g., American Robin is B-AMRO; species names with hyphens e.g., Chestnut-backed Chickadee is B-CBCH). See The Vertebrates of BC: Scientific and English Names, manual No.2 of the CBCB series for standard codes.
• For each bird encountered, record species, age, sex and activity.
• When a nest of interest is located during a survey, refer to the Nest Site Description Form to determine the data attributes to be collected.
• Refer to Figure 2 for a visual representation of the field procedures.

Figure 2. Sample layout for a presence/not detected survey of songbirds using a combination of encounter transects and point counts.

• Encounter transects
• Using the prepared base map identify (preferably randomly) the starting point of the transect. Before starting your survey, record the required transect information and weather conditions at the top of the dataform: Animal Observation Form - Songbird Encounter Transect & Simple Point Counts.
• Walk at a rate of 0.5 - 2 km/hr, stopping (at most 30 s) when appropriate to record data, identify birds, or listen.
• For each bird detection, record the distance traversed along the transect. In situations where there are large numbers of birds, break the transect down into 50 m recording sections.
• Note that all birds encountered along the transect must be recorded. It is not required that the distance from the transect to the observed birds be recorded for presence/not detected surveys.
• Each transect should be short enough that it may be surveyed in one morning.
• Point Counts
• Place the first point count station at the start of the transect.
• Space point count stations a minimum of 200 m apart. Point counts should be spaced far enough apart so observations at each point are independent from other stations.
• Wait one minute after arriving at the station before beginning to count all the birds detected. Create a label on your dataform for each Point Count Station so that observations can correspond with it.
• Count detected birds for a set time period. The standard period is five minutes per point count. Some surveys may want to use a shorter (minimum three minutes) or longer time period. This is acceptable, provided detections are categorized into the standard time intervals of zero to three minutes, three to five minutes and five plus minutes.
• Count and record all birds, regardless of distance detected from the point. For presence/not detected surveys, the radius of detection is unlimited. (Note: if the objective of the inventory is presence/not detected in a small, narrow or very patchy habitat, the detection radius should reflect this.)

Data Entry

The Design Components for this survey are transects and point count stations. However, in this case observations are grouped by transect. When digitally entering your survey data, choose `Transect' from the `Design Component Type' picklist.

Data Analysis

The analysis with presence/not detected data depends on the objective of the inventory effort. The table below highlights suggested analysis methods for the given RIC objectives.

Table 4. RIC objectives and analysis methods for presence/not detected data.

RIC Objective	Analysis methods	Program
Document species range	Analysis to ensure adequate effort. Negative binomial estimate1	See RIC manual No.1, Section 5.2
Determine habitat associations	Logistic regression	Generic statistical analysis software
Detect change in distribution over time	Use relative abundance methods and regression techniques.	Generic statistical analysis software

¹ See RIC manual No.1, Section 5, for more details on negative binomial methods.

Quantifying probability of detection: The main purpose of these methods is to document species geographic ranges. From a statistical point of view it is important to attempt to quantify the detection probability (as a function of population density, population spatial distribution, detection probability, sampling effort, and other covariates) for a species to allow a general estimate of the optimal amount of effort needed for surveys. Also, if an attempt is made to quantify probabilities of detection, a more statistically conclusive statement can be made about possible reasons for not detecting a species as opposed to a simple "none were found" conclusion. A simple way to estimate probability of detection is through the use of the negative binomial distribution with data from relative abundance surveys. This procedure is detailed in RIC manual No.1, Section 5.

Documenting changes in species distributions: If the objective is to detect changes in geographic distributions over time, a more intensive survey regime using relative abundance methods is recommended. This will allow a probability level to be associated with changes in distribution or apparent local extinction. A conclusion that species have become extinct in an area using presence/not detected methods will be difficult given that no estimate of survey precision is possible using current methods. More exactly, it will be difficult to determine if a species is not detected is due to lack of sample efficiency or actual demographic extinction.

Documenting habitat associations: If determining habitat associations is an objective, it will be important to document habitat types at the scale of songbird home ranges.