Birds As Environmental Indicators

Question 1

What sort of questions can bird studies answer?

Answer 1

Which species are present in an area
Number of individuals in each species
What habitat features make an area particularly good for a species
Which species are good environmental indicators
Changes in individuals/species from one year to the next
Why certain species are present

Question 2

What is important about the where whens and hows of bird censusing?

Answer 2

Where - geographical
-habitats
when - time of year
how - point counts
-transects
-mapping territories

Question 3

What are the key aspects of data collected?

Answer 3

Identification - species: appearance and song
Number of individuals - age/sex, activity, count-all/sample
Distribution changes due to - climate change, habitat change or pollution etc
Behaviour - wintering, migrating, breeding etc

Question 4

Describe kingfisher distribution and abundance

Answer 4

Mixed distribution and abundance, higher in Scotland and the East and lower in Ireland

Question 5

Describe barn owl populations

Answer 5

Distribution declining from 1968-1988 but increasing in many areas from 1988-2008
Adversely affected by DDT’s in the 1960’s

Question 6

Describe the population of Egrets

Answer 6

Was very rare with only 3 places recording them
Now egrets have become resident birds throughout Britain
Could be due to climate change eliminating the birds need to migrate

Question 7

What has caused a decline in the amount of farmland birds seen today?

Answer 7

Land management changes - monocultures

• move from Spring to Autumn sowing of arable crops
• Increased pesticide and fertiliser use
• Removal of non-cropped features such as hedgerows

Question 8

What positive steps can farmers take to conserve birds on their land?

Answer 8

Provision of over wintered stubbles
Provide seed in the winter
Uncropped margins on arable fields
Sympathetic management of hedgerows
Reduced use of chemicals

Question 9

Describe yellowhammer reduction

Answer 9

Began to decline in the mid 1980s declining ever since
Listed as green in 1996 now qualifies for the red list
Reductions in winter seed food availability as a result of agricultural intensification are widely believed to have contributed to the population decline - loss of winter stubbles and reduction in weed densities

Question 10

Describe lapwing decline

Answer 10

England and Wales population halved from 1987 to 1998
Changes in clutch failure rates due to increased grazing intensity and increased predation
Winter habitat change may also influence population decline
- loss of old grasslands (higher worm density)
-reduced use of manure as fertiliser
-pesticides that kill non target animals (worms)
-high sheep density

Question 11

Describe corn bunting decline

Answer 11

Decline in mid 1970’s
red list, local extinction from parts of it range
Breeding success per clutch has improved but fewer 2nd clutches laid, reducing overall productivity
Reduction in seed availability over winter

Question 12

Why is organic farming better for birds?

Answer 12

Larger hedgerows
Spring sown cereals present
Field diversity higher
No pesticides

Question 13

Why are birds valuable as environmental indicators?

Answer 13

High in the food chain - sensitive indicators
Occupy a wide range of habitats
There are long term data sets on bird populations
Birds are important as pest control in agricultural areas

Question 14

What factors affect species diversity?

Answer 14

Time
Space
Competition
Predation
Environmental stability 
High productivity

Question 15

What types of sampling are there?

Answer 15

Random sampling - random points in a defined area
Stratified random sampling - divide area and randomly select samples within area
Systematic sampling - regular points on a grid

Question 16

What factors affect sampling outcomes?

Answer 16

Time spent doing activity
Area of which the sampling takes place
Number of samples taken in each area
Positioning of the sampling effort
Weather
Practical considerations - access, equipment etc
Identification skills and expertise

Question 17

What are the three site survey types?

Answer 17

Point
Transect
Mapping

Question 18

Main points about point counts

Answer 18

Stand at one spot and make a count
- repeat this at a range of points to assemble a list of spp. In the area
- can be used to measure relative abundance in conjunction with other work (Reynolds et al 1980)
Large data sets with minimal effort
Problem - hard to standardise, hence uncertain variability - densities are estimated based on radius from observer
National method America and France
Preferred in woodland not open habitats

Question 19

Main points on Transect surveys

Answer 19

Fieldwork involves 3 visits
- first visit to determine route and record details of the habitat
- second and third are to count birds
Route is 2 parallel line roughly 1km in length
- split into 5x200m and birds are counted at each point
- 2nd visit ideally May and 3rd early June (4 weeks apart) to ensure late arriving migrants are recorded
Recorded within three bands - 25-100m, >100m and those in flight

Question 20

What are some sources of sampling bias?

Answer 20

Bird activity
Observer speed and effort
Species behaviour
Season
Time of day
Weather

Question 21

How does bird activity affect sampling bias?

Answer 21

The abundance is almost always measured less than the true number
- can see 4 birds but 7 present
- can hear 1 bird but 4 present
It is only required though that this proportion to the true number remains constant throughout testing

Question 22

How does observer speed and effort affect sampling bias?

How does species behaviour affect this also?

Answer 22

More birds seen if more effort is expended
A fast survey will miss quiet, skulking species (bullfinch)

Spp. Beh. - noisy species are easier to find

Question 23

How does bird density and bird habitat influence sampling bias?

Answer 23

Bird density - too many birds to locate, recognise and count. May be recounts of same birds
Habitat - birds are more conspicuous in open habitats than in woodlands and so variability is increased

Question 24

How does season and time of the day affect sampling bias?

Answer 24

Season - Bird spp. Sing over different periods of the year
In UK native spp. may have finished singing before African migrants arrive
Time - activity and song output are highest at dawn and dusk and lowest at mid day

Question 25

What four Atlas’ have the BTO created for comparison of birds over time and location?

Answer 25

Breeding Atlas I - fieldwork (1968-72)
Winter Atlas - fieldwork (1981/82-83/84)
Breeding Atlas II - fieldwork (1988-91)
Breeding Atlas III - fieldwork (1997-2011)