BIRD SURVEY TECHNIQUES
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Transcript of BIRD SURVEY TECHNIQUES
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