Population Counting Method Line transect, Point count, Mark and recapture

1. Population Counting Method:
Line transect, Point count, Mark
and recapture
Submitted by:
Tarique Bin Aziz
BSc. (Honors) in Zoology
MSc. In Wildlife and Biodiversity Conservation
Jagannath University

2. Line transect
• Line transect is a tape or string laid along the ground in a
straight line between two poles as a guide to a sampling
method used to measure the distribution of organisms.
• Ecologists use this method to investigate any community.
This method surveys a small section of a natural area. Line
transects can be walked, driven, swum or flown.
Estimating abundance of a relatively large and
conspicuous species, it is one of the best method.

3. Line transect cont.
 Assumptions
• No animals are missed
• Transect is a straight line
• Every detection is independent
• Points/objects are fixed at initial sightings and they do not
move before being detected

4. Line transect cont.
 Advantages
• More economical
• Greater species turnover
• Larger area is covered in relatively shorter time
• Applicable throughout the year
• Permanent transects can be monitored for a longer period of
time
• Can be used in most of the habitat types (except wetlands)
• With little care can also be used for hilly terrain
 Disadvantages
• Distances are not correctly measured
• Movement of observer may disturb the animals
• Chances of missing rare or shy species are great

5. Line transect cont.
 Method:
• The essential feature of line transects is that one walks
along a straight path and records the individuals seen and
their perpendicular distance from the transect line.
• Line transects are best used for visible animals in open
habitats. The sample size should be at least 40 sightings,
and better results are obtained from 60–80 sightings.
• Not all individuals need to be seen for this method to work.

6. Line transect cont.
Plate No. 1: Method of Line transect

7. Line transect cont.
• An illustration of the basic measurements that can be
taken for each individual sighted along a line transect in
the direction indicated by the arrow. The key measurement
is the perpendicular distance (xi). If the sighting distance
(ri) is easier to record in the field, the sighting angle (θ)
must also be measured.
The perpendicular distance x = r sinθ

8. Line transect cont.
 Strip transect Method:
• Strip transect method is a customize method of line
transect method
Plate No.2: Strip transect Method

9. Point count
• The simplest method of counting birds is called a "point
count", in which a trained observer records all the birds
seen and heard from a point count station for a set period
of time. A series of point counts completed over a fixed
route can then be compared to the results of the same point
counts in other seasons or years.
• Point Counts can be imagined as transects of zero length
conducted at zero speed.
 Types of Point Count:
1. Plot Counts (fixed radii for all species)
2. Point Counts with variable radii, by species
3. Point Counts with unlimited radii (Total Counts)

10. Point count cont.
 Assumptions
• Birds do not approach the observer or flee.
• All the birds are detected at the point of the observer.
• Birds do not move much during the count period
• Birds behave independently of one another.
• Distance estimates are accurate
• Birds are fully and correctly identified.

11. Point count cont.
 Advantages
• Less time consuming
• Duration can be controlled
• Total attention to detect birds
• Small homogenous habitats can also be studied
 Disadvantages
• Generating bird list is slower
• Many species are missed
• Area sampled in one unit is small

12. Point count cont.
 Methods
• Points to be counted are to be laid out systematically or
selected randomly in the study area.
• Points should ideally be 200 meters apart to avoid double
counting.
• In a small area, lesser points should be monitored to avoid
duplication
• In small patches of habitat, inclusion of points near the
edges should be done with caution depending on the
objectives of the study.

13. Point count cont.
Count duration:
• It can vary from 2-20 minutes
• Record only these birds seen during Count duration. Do
not include for analysis those birds seen while walking
between two points.
 How far Point counts should be done ?
Not very far (> 200 m)
Not very close (<20 m)
Ideally 50 to 100 m apart

14. Point count cont.
 At what time it should be done ?
• 15-20 minutes after sunrise
• Evening counts can be done
 How to record distance ?
• Record bird’s distance from the observer (yourself)
• Record distance in categories (0-25m, 25-50m and >50m)

15. Point count cont.
Plate No.3: Point count Method

16. Mark and recapture
• Mark and recapture is a method commonly used in ecology
to estimate an animal population's size.
• A portion of the population is captured, marked, and
released. Later, another portion is captured and the
number of marked individuals within the sample is
counted.
 Estimating Population Size =
Number marked in first sample X Total caught in second sample
Number marked in second sample

17. Mark and recapture cont.
 Assumptions
• Individuals with marks have the same probability of
survival as other members of the population.
• Births and deaths do not occur between the time of release
and the time of recapture.
• No immigration nor emigration between the time of release
and the time of recapture.
• Marked individuals mix randomly with the population at
large.
• Marked animals are neither easier, nor harder, to capture a
second time.
• Marks do not come off of the marked organisms.
• Recapture rates are high enough to support an accurate
estimate.

18. Mark and recapture cont.
 Advantages
• good method for detecting shy, skulking animals
• very rich source of information
• confirmed identification
• photographic evidence available
• very good learning process
 Disadvantages
• labour intensive exercise
• problems of permissions
• costly and time consuming
• ringing training and license required
• not good for short rapid surveys
• animals become net shy

19. Mark and recapture cont.
• This method can be expressed symbolically as follows-
n1 = the number of animals first marked and released
n2 = the size of the second sample
m2 = the number of marked animals in that sample
N = the total population size
Then we expect that , m2/n2 = n1/N
It is obvious that, since n1, n2, and m2 are known, N can be
estimated.
All mark–recapture methods rest on this basic idea, though
most entail animals being caught and marked on several
occasions.

20. Mark and recapture cont.
No individuals enter or leave the population between surveys
Survey 1 Survey 2
 Population parameter estimation:
 Closed populations:

21. Mark and recapture cont.
 What makes a population closed?
1. Dispersal barriers
2. Philopatry
3. Large surveyed area
4. Slow reproductive/death rate
5. Short time between surveys
 Closed populations can estimate through these method-
1. Petersen method
2. Schnabel method
3. Schumacher-Eschmeyer

22. Mark and recapture cont.
 Open populations:
 Individuals enter or leave the population between surveys.
 Open populations can estimate through Jolly Seber method.
Survey 1 Survey 2

23. Mark and recapture cont.
 Variance and standard deviation
• Variance (and standard deviation) are measures of how
spread out a set of results is.
• This is known as distribution (it is not how spread out the
bees are in the environment).
Variance and mean:
The Variance (σ2) is calculated as the average squared
deviation of each number from its mean.
The formula (in summation notation) for the Variance in a
population is-
𝝈 𝟐 =
𝑿 − 𝝁 𝟐
𝑵

24. Mark and recapture cont.
Here,
Ʃ (summation) = sum of all values in range of series
X = each value in the range
μ = mean
N = number of scores
For example, for the numbers 1, 2, and 3, the mean is 2 and
the Variance is:
𝝈 𝟐 =
𝟏 − 𝟐 𝟐 + 𝟐 − 𝟐 𝟐 + 𝟑 − 𝟐 𝟐
𝟑
= 𝟎. 𝟔𝟔𝟕
Standard Deviation:
The Standard Deviation is the square root of the Variance.
𝝈 𝟐

25. Conclusion
Those are the population counting methods. So,
which we can estimate abundance and density of
population in an area.

26. Thank You….