BIRD SURVEY TECHNIQUES

Based on the manual prepared bySalim Javed & Rahul Kaul

Bombay Natural History Society

     

WWhy Count Birds? Fundamental questions Elemental arithmetic tendency to count Necessary to devise a strategy and new plans Doing something in a systematic manner Interesting and necessary to know more about birds

WWhere to count?

Any area – garden, orchard, park, forest, wetlands, grassland, desert

Unstudied area Important staging area Threatened area Sanctuary or a national park Research site(s)

WWhen to count birds?

Breeding seasonWinter counts Seasonality and timing of count is very important During migration

How to plan a survey

Permission from forest department/ relevant authorityMake local contactsLogistics i.e. places of stay, routes etc

Necessary fundsArea maps: Toposheets, vegetation maps, aerial photosLiterature (checklist of birds and plants, reports, research papers, working plan) Data sheets, pen, field note book, padEquipment: Binocular, camera, compass, altimeter, GPSFieldguides, reference books and papers

Which site(s) to select

We have to ask the following questions:

What is the purpose of census? IBA or EBA Sanctuary or National Park

Size: logistics, time frame, budget and the size of the team

 

Strategies

A. Non-sampling strategy Total count in an area

e.g. Siberian cranes in Keoladeo

Nest count e.g. Greater Adjutant stork colony

Territory mapping e.g. Bengal florican display grounds

B. Sampling strategy

Counting a small representative population and then extrapolating about the total population

e.g. random, stratified or systematic random

Important points to remember -

Do not unnecessary collect large data Maximize your efforts Determine sample size Collect right type of data

To determine effective sampling efforts, first answer - Two major questions 1. How many samples to take? 2. What should be the plot size so that most species are covered ?   To answer these questions, we need to plot Species Discovery Curve.

Species Discovery Curve is plotting of number of species detected or discovered per unit of sampling efforts (length of transect, time spent walking a transect or standing on a point).

 

Species discovery curve showing a cumulative total of species seen in riparian habitat in Dudwa National Park, India over a 30 day period

What is distance sampling? 

Distance sampling involves collection of data where distances of objects are

estimated or measured.

e.g. Line transects

Point Counts

Cue counts (calls, territory)

WWhat is Line Transect ?

Line transect is based on the theory of walking along a predetermined route at a regular interval to record the Birds on or near the line.   

Methodology or Study Design

A. Site Selection

Random or systematic Stratified : covering different habitats within the

study area Stratified random: randomly choosing areas in

different habitats

B. Where can one monitor Line Transects?

Best in open, flat habitat Also conducted in hilly areas Homogeneous habitat preferred  C. Where to place Line Transects

accessibility and terrain straight line, not zig-zag avoid along roads, streams or contour of hills well spaced out (minimum 200 m apart) random, stratified or linear (hilly terrain)

D. Permanent or Temporary transect

If permanent - mark with stones or colour posts (trees) divide the transects in to 40-50 m segments 

E. What should be Transect Length?

It varies according to species, habitat and aim of study

single species study community study rare or common species diversity of habitat How to determine transect length?

preliminary checklist

few test runs

species area curve

What is Species Area Curve ?

Species area curve is drawn by plotting the

sighting frequency of

birds with increasing

transect length. After a point, species

discovery curve tends to stabilise, which means

that with subsequent increase in the line of the

transect there is little or no corresponding

increase in the new species being added. The

point

at which curve flattens out (asymptote)

can then be considered as adequate for

sampling birds.

 

35 

SPECIES 

5

100100 200 300 400 500 600 700200 300 400 500 600 700

Transect Length in metersTransect Length in meters

Species area curve for obtaining the length of Species area curve for obtaining the length of the transectthe transect

E. What should be the speed of travel? walk in standard pace (about 8-10 m/minute) time duration should not vary more than 10% among transects   

F. What time of the day? preferably morning 15-25 minutes after sunrise continue for 2-3 hours 

  G. In which weather condition? sunny weather avoid raining or windy days keep tract of weather condition of study area

H. How often (periodicity) ? weekly or fortnightly or monthly (intensive study)

seasonal (long term study, 5-10 years) once or twice a year (very long term study, 20-25

years or more) I. How many replicates ?

Minimum two replicates of each transects Minimum of 6 monitoring in each season

 

J. Open width or fixed width ? Open width: All birds are noted irrespective of their

sighting distance  Fixed width or Belt transect: Birds seen up to a certain distance (width on either side of transect length) are only noted

 

Biases in census counts Observer bias Effect of habitat Bird behaviour Weather

  

How to do analyses of the collected data?

A. Simple method :

n D= ----------------- 2L x Y

 

n= total number of individuals; L=length of the transect; Y= mean perpendicular distance

B. Computer programmes: 1. TRANSECTS-II 2. DISTANCE

How to determine the width distance?

It depends upon the birds being censused and type of habitat. 

Data collection What to record ?

number of individuals of a species

perpendicular distance

sighting angle and sighting distance

sex (male, female if possible)

age (adult, juvenile)

activity (singing, foraging, flying, etc)

substratum (ground, bush, tree etc) 

If the bird is not seen but heard, records its call and try to judge the distance.

15

INDIVIDUALS

2

Perpendicular Distance

Frequency histogram of perpendicular distances (number of individual detected decrease with increasing distance from the line)

Question: What is perpendicular distance? Answer: Perpendicular distance is the distance of the bird from the transect line.  

Should we record the exact distance?

Recording exact distance is difficult (e.g. 11 m, 16 m)

Therefore, record in group intervals (0-5m, 5-10m, 10-15m).  

PD= Perpendicular Distance SD= Sighting Distance O= Observer L= Transect Line = Object

PD SD

L

 

 

 Recording of perpendicular distances and sighting angles in line transect sampling

The Fourier series (FS) estimator used in the analysis is the expansion of probability density function (pdf), f (x). Fourier series estimator is a robust non-parametric procedure in which the difference in detectability between different habitats is taken care of by pooling robustness of FS estimator and its estimation efficiency.

n F (0)

D = --‑‑‑‑‑‑‑------

2L   n = Total number of bird groups seen; L = Length of the transect F (0) = Probability density function

Distances10, 12, 15, 5, 10, 25

N= No of objects L= Length of transect Y= Mean perpendicular

  D = n / 2LY = 6 / 2 x 500 x 12.8 = (6 / 12800) x 10000 = 4. 6 birds / ha

 

A simple way of calculating density from ungrouped perpendicular distances

N = 6

L = 500

Y = 12.8

Advantages of Line Transect       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 of Line Transect         Distances are not correctly measured      Movement of observer may disturb the birds      Chances of missing skulking or shy birds are great

 

    

Assumptions of Line Transect

No bird is 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 

Precautions to be taken:  

Try to keep line as straight as possible 

Make special effort to find those birds that are close to the transect 

Distances should be measured correctly 

Transect should be long enough to allow detection of at least 40 individuals 

Transect should be representative of a habitat 

Observer must be interested, competent and trained

Point Count Method

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)

 

What are the 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.

Advantages of Point Counts

less time consuming

duration can be controlled

total attention to detect birds

small homogenous habitats can also be studied  

Disadvantages of Point Counts

generating bird list is slower

many species are missed

area sampled in one unit is small 

How to select points for counting ?

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. 

What should be the 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

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)

Data recording

1. Number of individuals of each species detected within a 20-25 m radius surrounding the observer. The radius will vary depending upon the habitat type.•2. Number of individuals of each species detected beyond the 25m radius but still within the same habitat.•3. All individuals detected while the observer walked between count points are recorded but the data are not used in the analysis. Species recorded during this period will contribute to the completeness of species list for the site.•4. Birds that originally were detected outside 20-25m radius boundary but later move within 25m of the observer are recorded as occurring within the fixed radius circle. This facilitates comparison among vegetatively different habitats. Objective is to count each individual bird once and only once.

Analysis

density, species diversity, richness and species composition can be calculated  enter large data in EXCEL and LOTUS  sample data matrix can be generated using SPECDIVRS.BAS. follow the instructions given in statistical books and/or take help of a good bio-statistician

Example of a data sheet for point count used in Ranikhet, Kumaon Himalayas

 

POINT COUNTDate Locality Altitude Habitat Observer

SalimLat Long Slope Weather Sheet #Time Start Time End Visibility Aspect

Sr. No. Bird Species Time No. Sex Age Distance Height Activity Plant spp. Hgt. Remarks

1. Blue Whistling Thrush 0710 2 - - 10 m 0 m Foraging - -

2. Minivet 0810 4 - -- 5 m 1 m Foraging - -

3.

4.

 

Comparison of transect and point count census methods____________________________________________________________________________________________________

S. No.

Items

Transects Point Counts Duration

____________________________

Short

Long____________________________________________________________________________________________________

1. Saturation of observer with cues from bird

Little

Some

Much2. Birds moving into and out of the range

Few

Some

Many3. Speed of generating species list

Fast

Medium

Slow4. Birds missed by flushing

No

Yes

Yes5. Skulking birds missed

Yes

No

No6. Total count/unit line

Same

Same

Same7. Attention divided

Yes

No

No8. Area sampled in one unit

Large

Small

Small9. Bias

Small

Small

Small10. Precision

High

High

High____________________________________________________________________________________________________

Desirable method= Small bias and high precision

Species Richness MethodsSpecies richness methods are simple methods of counting or generating species list and then making useful interpretation from them. Depending upon the area, type of survey, whether single species or multi-species, a species richness method can be conducted.   

Types of species richness methods

1. Encounter Rates 2. McKinnon’s Species Richness Method3. Timed Species Count4. Mist netting

 

1. Encounter Rates

species seen per unit efforts (time, distance etc)useful for single species or multiple-species surveys data gives only relative abundance not density

It gives number of birds/unit area or number of birds/unit time that can be compared with other habitats/areas/seasons.

 

 

   

 

Data Sheet

Data sheet for collecting encounter rate data DATA SHEET__________________________________________________________________________________Date Locality HabitatTime Start Time End Weather Visibility Aspect SlopeAltitude Coordinates Observer SJTransect/Trail Length Transect # Sheet #  __________________________________________________________________________________ Bird Species Time Flock Size Habitat Sex Age Activity   __________________________________________________________________________________Roseringed Parakeet 0645 2 MF M A PerchingRedvented Bulbul 0650 1 MF - SA FeedingGreen Bee- eater 0700 4 MF - A Perching

 

A common method of presenting encounter rate data________________________________________________________________________________________________________________________________

Sites No. of birds No. of hours Birds/hour Transect Length Birds/km________________________________________________________________________________________ Site 1 2 5 2/5 3km 2/3=0.6/km Site 2 3 2 3/2 2km 3/2=1.25/km Site 3 5 3 5/3 2km 5/2 = 2.5/km________________________________________________________________________________________

How to present multi-species survey data?

Calculate encounter rate of each speciesEnter data in EXCEL or LOTUSPresent data in descending order or classification-wiseCategories the encounter rate (very common 20-25 sightings; common 15-20 sightings; etc)

Encounter rates from a multi-species survey from a standard one hour walk at each site

________________________________________________________________________________________________________________________________

Species Site 1 Abundance Site2 Abundance______________________________________________________________________________ Rose-ringed Parakeet 5 5/hr 2 2/hr Ring Dove 2 2/hr 1 1/hr Green Bee-eater 0 0/hr 2 0/hr Emerald Dove 4 4/hr 1 4/hr Red breasted Flycatcher 1 1/hr 0 0/hr_____________________________________________________________________________________________________________________

Common: 5-10; Very Common: 10-25; Uncommon: 1-5

Advantage of Encounter rate data

quick and easy method, especially in hilly terrain easy calculation data comparable across sites/seasons/habitats diversity and richness can be calculated

2. McKinnon's Species Richness Method

developed by McKinnon & Philip (1993) in Indonesia.

quick and easy to know richness

useful for rapid surveys in difficult habitats

useful for multi-site surveys

What is the methodology?

walk in an area till a given number of species are recorded the number of species could be 10, 15, 20, 25 or 30 but it should be constant for all the sites  once a given number of species(e.g. 20) have been seen, go to another area and record the same number of species (i.e. 20).  prepare 10 to 15 such lists from different parts of the study area common species will get recorded in several lists. in species rich areas, listing will be very fast note starting and ending times, habitat condition, weather etc.

Analysis

By plotting the cumulative total of species detected against the number of lists, species discovery curves can be produced.   This species discovery curve for each site is a measure of species diversity and can be plotted to compare several sites  If additionally numbers of individuals are also recorded these values can be used to compare species diversity based on discovery curve but also indices of richness and diversity.   Number of time a species reappears in subsequent lists can be converted into frequency of occurrence, which gives some idea about relative abundance of that species when compared with other species.  An index of relative abundance can also be generated by dividing the number of lists a species appears in by the total number of lists. An index between 0-1 is produced for each species.

Advantages of McKinnon’s Species Richness method The method is simple, quick and does not require any special

observer skills and equipment.  A very useful method for multi-species survey.  Can be used in difficult terrain.  Can be used for different habitats.

Precautions 

Each list should be independent   Lists should be made away from each other so same individuals

are not counted again.  For different habitats, separate lists should be prepared.  Number of lists should be according to available habitat.

 

Data sheet for recording species ___________________________________________________________________________________________________

_DATA FORMAT FOR McKinnon’s LIST

____________________________________________________________________________________________________

Sr. N. List 1 List 2 List 3 List 3

_______________________________________________________________________________________________

Species No Species No Species No Species No ___________________________________________________________________________________________________

_1. Roseringed Parakeet 1 Collared Bushchat 1 Small Blue Kingfisher 1 ………………. …..2. Ring Dove 2 Rubythroat 1 ………………. ….. ………………. ….. 3. Little Brown Dove 1 Black Drongo 1 ………………. ….. ………………. …..4. Green Bee Eater 5 Jungle Crow 1 ………………. ….. ………………. …..5. Collared Bushchat 1 Greyheaded Flycatcher 1 ………………. ….. ………………. …..6. Pied Myna 2 Shikra 1 ………………. ….. ………………. …..7. Purple Sunbird 1 House Crow 2 ………………. ….. ………………. …..8. Jungle Babbler 2 Purple Sunbird 2 ………………. ….. ………………. …..9. Crow Pheasant 1 Pariah Kite 1 ………………. ….. ………………. …..10. Purple Sunbird 1 Greyheaded Flycatcher 1 ………………. ….. ………………. …..11. Greyheaded Flycatcher 1 Grey Tit 2 ………………. ….. ………………. …..12. Redbreasted Flycatcher 1 Common Myna 1 ………………. ….. ………………. …..13. Chiffchaf 1 Golden Oriole 1 ………………. ….. ………………. …..14. Black Drongo 1 Redwattled Lapwing 1 ………………. ….. ………………. …..15. House Sparrow 2 Brahminy Myna 2 ………………. ….. ………………. …..16. Golden Oriole 1 Indian Roller 1 ………………. ….. ………………. …..17. Brahminy Myna 2 White Eye 3 ………………. ….. ………………. …..18. White Eye 5 Whitebreasted Kingfisher 1 ………………. ….. ………………. …..19. Yellowlegged Green Pigeon 8 Tailor Bird 1 ………………. ….. ………………. …..20. Tailor Bird 1 Roseringed Parakeet 3 ………………. ….. ………………. …..___________________________________________________________________________________________________

_

3. Timed Species Counts (TCS)Principle Common species are generally detected earlier than the rarer forms, therefore the time taken to detect a bird forms a measure of its abundance. 

Methodology  Take observations for a certain time, say one hour.  Divide one hour in six 10 minute time periods  All the species seen in the first 10-minute time period are recorded.   Then go to another site and record species not recorded earlier.  Repeat this six times, 10 minute period each  Never record a species twice.  Make a minimum of 10-15 visits to the study area at different seasons/months.  During each visit, try to cover at least 1 km2 area

 

Analysis 

All species recorded are ranked according to their time period. Thus, species recorded in the first 10 minute interval are ranked 6 followed by 5 for the species recorded in the second 10 minute interval and so on. Unrecorded species are ranked 0. An index of relative abundance of species is calculated as the mean score for each species across all survey visits to the site. Therefore scores between a maximum value of six and a minimum value of 1/n (n is the number of repeated surveys) are obtained.

Advantages 

simple, easy and quick amateur birdwatcher can do it  

Disadvantages

provides only crude relative indices of abundance. comparisons of different species within area or between areas can be made but these need to be interpreted with caution because of differential detectability of species in different habitats/areas. flocking species may end up with lower indices compared to the more widely dispersed ones because flocked species may not be recorded in subsequent time-periods once the flock has been recorded

Hypothetical data set to demonstrate the use of TSC method

0-10 mins 10-20 mins 20-30 mins 30-40 mins 40-50 mins 50-60 mins

Yellowbellied Fantail Flycatcher

White cheeked Bulbul

Kestrel Himalayan tree creeper

White Crested Kalij

Beautiful Nuthatch

Jungle Crow Long-tailed Minivet

Strong footed bush warbler

Yellow rumped leaf warbler

Streaked Laughing Thrush

 

Collared Bush chat

Grey Tit Verditer Flycatcher

Large Hawk Cuckoo

   

Slaty headed parakeet

Himalayan Griffon

  Black Drongo

   

Tailor bird Green backed Tit

       

Ranking of the above dataset using Timed Species Counts

________________________________________________________________________________________________________________________________

Species Visit1 Visit2 Visit3 Total rank score Mean rank score Species rank_______________________________________________________________________________________________________________________________

_Yellowbellied Fantail Flycatcher 6 3 2 11 3.66 10Jungle crow 6 6 6 18 6.0 1Collared Bush chat 6 4 1 11 3.66 10Slaty headed Parakeet 5 4 3 12 4.0 9Tailor Bird 5 4 1 10 3.33 14White-cheeked Bulbul 5 5 4 14 4.66 5Long-tailed Minivet 5 4 4 13 4.33 7Grey tit 4 5 4 13 4.33 7Hmalayan Griffon Vulture 4 3 4 11 3.66 10Green backed Tit 4 5 5 14 4.66 5Kestrel 4 3 2 9 3.0 16Strong footed Bush warbler 4 5 6 15 5.0 3Verditer Flycatcher 4 6 6 16 5.33 2Himalayan tree creeper 3 5 3 11 3.66 10Yellow rumped leaf warbler 3 3 0 6 2.0 17Large Hawk cuckoo 3 6 6 15 5.0 3 White crested Kalij 2 0 3 8 1.66 18Beautiful Nuthatch 1 0 0 1 0.33 20Streaked Laughing Thrush 2 1 1 4 1.33 19Black Drongo 3 3 4 10 3.33 14________________________________________________________________________________________

4. Mist netting

Principle By trapping birds in a standardized way, bird populations or communities of different sites can be compared.  

Methodology a fixed number of nets are operated for a fixed period of time at different sites. the birds caught by these nets are recorded, measured, ringed and released data are recorded in a format results are expressed as birds caught/net/hour

Analysis 

many ways of analysing data variations in population size and structure over years or between sites can be detected. species diversity and similarity indices can be generated to study the bird communities at various sites survival rates and productivity can also be examined using this technique by calculating the rate of adults to juveniles caught after the breeding period

Beside this, we also get longevity, survival, site-fidelity, moult, breeding and migration data.

Advantages good method for detecting shy, skulking birds 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 licence required  not good for short rapid surveys  birds become net shy

BiasesResults can be influenced by the way the nets are laid and the location where they are laid and therefore comparisons between sites may be difficult unless

sites selected are truly random.

BBreeding Bird counts Why count during breeding season? 

birds become comparatively conspicuous most birds sing or display most birds have territories during breeding season movement become restricted so easy to count many birds come back every year to same area for breeding some birds nest in colonies hence easy to count 

WWhat are the methods of counting breeding birds

1. Territory mapping 2.    2. Call counts3.    3. Nest counts

DG

A

B

FC

G

E

A

C

B

ABA

CC

J

HG

H

1. Territory mapping most birds, especially males defend territories song and display can be easily detected and pinpointed territorial males can counted and mapped density of singing males per hectare/sq. km can be calculated

 

Territory mapping for Painted Francolin from calls

Advantages provides good data calculation very easy can be graphically illustrated repeatable every year/season provide information about bird-habitat association

  Disadvantages

time consuming and expensive needs expertise and patience can be done in breeding season only could disturb the nesting birds

 Assumptions

Birds live in pairs in non-overlapping territories

2. Call Count

many bird species call during the breeding season.

good for Galliformes species

call can be counted from a strategic place

can be repeated every season

can be compared across habitats and sites

Methodology

most species have distinct calls

species can be identified by calls

observers sit 300-500 m apart and note every call

direction of call and time are also noted

before starting, observers synchronise watches

observations starts early morning when most birds call

counts should be stopped 15-20 minutes after the first call

is heard

Analysis

observers sit together and compare call locations

duplicate records are deleted

after the records have been pruned, the minimum number of birds calling is noted

density of calling birds is estimated from the total study area

Advantages, disadvantages and biases

excellent method for vocal but skulking birds

non-invasive method and does no disturb the birds

simple and does not require much equipment

easy to monitor trend for a number of years

birds can be stimulated to call by call play-back

fairly accurate estimates of abundance indices

 

Disadvantages

difficult to identify call and distance by inexperienced observers

counts have to be repeated 4-5 successive mornings to account for

the large variation in calling of birds.

birds may also be over-estimated if call counts are conducted for

long durations

birds tend to shift their locations after initial calling and there is a

chance that a bird might be counted twice if call counts are

prolonged.

day to day variation in number of calling males

density estimation of calling males or pairs only, not of non-

‘breeding individuals

N

Observer

T1

K1

K2

T2

K3

 

 Call count sheet commonly used for counting pheasants

 

3. Nest Counts

over one-eighth birds nest in colonies nests or pairs of a colony can be counted or estimated nest site fidelity is seen so birds come to same area every year breeding population can be estimated easily comparative data can be obtained across years/sites photography can be used for estimation/counting in small colonies, total nest can be counted in large colonies, sample surveys can be done  

Advantages 

easy and interesting generates good statistical data generates media interest in conservation easy to monitor from year to year 

Disadvantages

may disturb the birds if not done carefully the whole colony may not be approachable nests in dense colonies are not easy to count

Caution  

Most species of birds are sensitive to disturbance during the

breeding season, so extreme caution should be taken while counting the nests or pairs. It is preferable to count the nest from a distance. Nest count can also be made after the breeding is over (e.g. flamingo, pelicans). A bare minimum time should be spent near a nesting colony. Most counts should be done in the morning or evening, and never during hot mid-day.

In protected areas, first get permission from the forest

officials.

If you cannot follow rules,

DO NOT COUNT