Ecology and the Habitat of Birds

Female Wheatear on Migration (Conwy, North Wales)

Image by Cj Roberts via Flickr

Ecology has been described as ‘scientific natural history’ and this is still a valid description. Another definition of ecology is the ‘study of animals and plants in relation to their environment’. Professor Eugene Odum, a well-known American ecologist, stated that it is more in keeping with modern emphasis to define ecology as the study of the structure and function of habitats or the places where birds and other animals, as well as plants, live. He and other scientists like him, were particularly interested in the transfer of energy through the ecosystem (the community of living and non-living material in an environment), and how this energy, contained in the food or nutrients moves through the different levels. Basically, the cycle begins with the chemicals from the non-living material, such as rocks, being absorbed by the plants. These are eaten in their turn by animals, which may be eaten by other animals and which finally return to the soil in one form or another. This process is usually assisted by organisms which break down the dead protoplasm.

This type of study generally speaking is beyond the ability of the average birdwatcher with limited time at his disposal. However, we do have wonderful opportunities to observe birds in relation to their environment and observe how these needs are met by the various components of their habitat.

Even within its normal geographical range a bird does not have a completely continuous distribution and this may be affected by several physical factors, such as temperature, light, the presence or absence of water, and the shape of the terrain. These in turn affect the vegetation and animal life and their inter-actions. The impact of all these factors shapes a bird’s ‘niche’ which is defined as a bird’s role within an ecosystem and its living place in the habitat. For example, in the Context of its ‘niche’ the Wheatear could be broadly described as an insectivorous bird, which lives on open ground, including heavily grazed grassland and mountain plateaux and avoids any form of thick cover, though it nests in holes or burrows. While, by contrast the Robin could be described as a mainly insectivorous bird which lives in rather dense woodland and woodland edges, rarely staying long from cover, and nests in holes.

Apparently a bird recognizes its habitat instinctively. On Skokholm the most heavily grazed grassland in the centre of the island attracted Wheatears during the autumn passage, while on the spring migration they tended to settle on the outer edges of the island where the soft peaty soil was riddled with thousands of holes excavated by rabbits and seabirds, and which was representative of the Wheatear’s preferred nesting area. Thus apparently their ‘image’ of their habitat differed according to the time of year.

A number of systems of classifying habitats have been described over the years, but none of them has been completely satisfactory perhaps, because, as Charles Elton points out, no single kind of animal is entirely confined to one component type of habitat. Another source of confusion is the tendency of ornithologists to use botanical terminology to describe a habitat. This, to my mind, is not entirely satisfactory as birds tend to be more affected by such factors as the age or the density or the size of trees in a wood, as much as by the species.

The system of nomenclature for habitats which is most generally used today is based on a system originally devised by Charles Elton in his book The Pattern of Animal Communities published by Methuen, which is one of the best natural history books ever written and not read by nearly enough amateur naturalists. In approaching the problem of describing habitats, he says: ‘Any ecological classification of habitats needs to fulfil three requirements. The first is to divide up the landscape and its species network into different components that can be defined by discontinuities in the field; the second is that components of one kind should be recognizably similar though they can never be exactly so; and the third is that they should have some ecological meaning, that is contain groups that form communities in some real sense of the term.’

The BTO has produced a habitat classification for its ‘Register of Ornithological Sites’ and for other surveys. It is on two levels of hierarchy and can be used to describe in general terms the breeding habitats of most birds.

 

o. Woodland and scrub

0 Broad-leaved woodland (other than coppice)

1 Coppice

2 Even-aged coniferous plantation

3 Uneven-aged coniferous plantation

4 Mixed woodland

5 Pioneer scrub

6 Carr (fen woodland)

  

1. ‘Field’ vegetation 

0 Bracken

1 Chalk downland and similar grasslands

2 Machair (natural grassland on calcareous sand)

3 Lowland dry heath

4 Upland heather moor

5 Upland grasslands

 

 

 

2. Wetlands (vegetation associated with fresh water) 

0 Bog

1 Wet heath or heath bog

2 Fen and marsh

3 Watercress beds (used and disused)

4 Reedbed

5 Turlough (grassy hollow on limestone)

6 Watermeadow and wash 

 

3. Water bodies (fresh) 

0 Lowland river or stream

1 Upland river or stream

2 Ditch (artificial, less than 5 metres wide)

3 Canal (artificial, more than 5 metres wide)

4 Pond (less than 05 hectares)

5 Pool or tarn (05 to 5 hectares)

6 Lake or reservoir (more than 5 hectares)

7 Other water body, e.g. gravel pit or flash (less than 05 hectares)

8 Other water body (05 to 5 hectares)

9 Other water body (more than 5 hectares)

 

4. Open habitats (not coastal)

0 Exposed ‘mud’

1 Exposed quarry face (sand, chalk, etc.)

2 High montane

3 Cliff and crag

 

5. Coastal

0 Mud

1 Saltmarsh

2 Coastal grazing marsh

3 Brackish pools and lagoons

4 Gravel and pebbles (beach, bar, spit, etc.)

5 Sand (flats or beach)

6 Sand dunes

7 Dune slack

8 Cliff

9 Stack or rocky island

6. Miscellaneous

0 Farmland, predominantly arable

1 Farmland, predominantly grazing

2 Farmland mixed

3 Hedgerows with mature trees

4 Hedgerows without mature trees

5 Disused railway track

6 Grassy areas with scattered trees (parkland, golf courses, etc.)

7 Sewage farms or purification works

8 Building and constructions

9 Waste land

 

This system is fine for describing general habitats but when dealing with differences between the habitats of some closely related species such as the Garden Warbler and the Blackcap you will run into difficulties, and will have to work out your own methods. Concentration on every little detail is often required to discover what limits a bird to a particular habitat.

03. October 2011 by admin
Categories: Ecology/Habitat | Tags: , , , | Comments Off on Ecology and the Habitat of Birds

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