Census Techniques

Question 1

Sources of Bias

Answer 1

Observers
Habitat
Birds
Weather
Technique

Question 2

Observers Bias

Answer 2

eyesight, hearing (especially males

over 40), id skills, equipment

Question 3

Habitat Bias

Answer 3

dense, noise from roads, rivers, wind,

terrain

Question 4

Birds Bias

Answer 4

behavior, sensitivity to disturbance,
mobility, flocking, detectable, territories, diurnal,
time of day

Question 5

Weather Bias

Answer 5

wind, rain, fog, extreme temperature

Question 6

Technique Bias

Answer 6

number of points, sampling plan

Question 7

Techniques

Answer 7

Mapping
Transects
Point Counts/Circular Plots
Scan/ Look See
Indirect Counts
Banding/ Mark Recapture
Flyway Counts
Juvenile/Adult Ratios

Question 8

Total Mapping

Answer 8

mark everyone-
home range or 
territory use, very 
expensive, get 
accurate count, 
endangered 
species, behavior 
studies

Question 9

Spot Mapping

Answer 9

Visit plot at least 8 times, systematic search, record all
birds heard/seen

Each cluster (at least 2 sightings/cluster) = 1 breeding pair
Edge problems
Very sensitive to plot size

Measure # pairs/area = density

Question 10

Line Transects

Answer 10

More efficient than mapping techniques

Best suited for homogenous areas where
vegetation and terrain do not limit travel, linear
habitats

Question 11

No Distance Line Transects

Answer 11

Travel transect- count all birds seen and
heard
Easy
No density estimate- only presence/absence
or relative abundance

Question 12

Strip Transects

Answer 12

Count all birds that occur in the strip, ignore birds
outside of strip
Strip is usually 25 m on each side of line
Only need to estimate 1 distance
Technique gives density measure
Detection can be a problem

Question 13

Emlen Transect- Variable

Distance Line Transect

Answer 13

Estimate distance perpendicular from
observer to each bird seen or heard
Can be difficult to estimate distance

Question 14

Variable Distance Line Transect

Answer 14

Often few birds seen close to line

Use Coefficient of Detection (CD) for each
species to correct for detection close to or
far away from line

*Density = (n(pairs)/length x width)CD

Question 15

Point Counts or Circular Plots

Answer 15

Newest method- replacing line transects
Good for linking habitat and birds, uneven terrain, dense
vegetation, fragmented habitat

Errors in distance measurement compound geometrically

Question 16

No Distance Point Counts

Answer 16

Count all birds seen and heard during count 
period
Easy
Relative abundance and presence/absence 
data- not density

Question 17

Fixed Radius Point Count

Answer 17

Like a strip transect- count all birds within circle
Only measure 1 distance

• Density = n (pairs)/pi r2

Question 18

Variable Distance Point Counts

Answer 18

Record distance from observer to bird
Don’t lose birds outside of circle

For each species calculate CD (coefficient of detection)
Density = (n(pairs)/pi r2
) CD

Question 19

Most Common Techniques

Answer 19

Transects and Point Counts

Question 20

Scan

Answer 20

Scan area and record birds
If area very large or many birds-
divide into sectors
Spend set amount of time 
scanning or on each sector
Good for open habitats where 
movements would disturb birds
Work quickly to avoid counting 
birds moving from one area to 
another

Question 21

Indirect Counts

Answer 21

No density estimates
Nest counts – Count apparently 
occupied nest
Roost counts
Fecal counts
Track counts (in mud, etc)