Cornwall Bird Atlas

CBA - How it all works

The CBA website is navigable in several ways.

To search for a particular species:

  1. From the Atlas home page click on either the winter or summer abundance or breeding species maps in the left hand menu.
  2. Select the species you wish to view (if a core species) or click ‘Rarer or Scarce species’ and select. This will draw up the county map. Rare or sensitive species are mapped at hectad level only. It is possible to switch from breeding to summer to winter and visa versa.
  3. In the abundance maps the black dots represent the relative abundance derived from the timed counts; ie where a species is more or less common. These are not absolute abundance levels ie an estimate of the total number of birds within a grid square. The relative abundance estimate is generally species specific and cannot be used to make comparisons between species because different scales may have been used.
  4. Grey dots indicate the maximum counts for the period. In some cases these are quite small and difficult to see. Hovering over the ‘Hide topography’ reveals the grid outline and small dots are more visible.
  5. It is possible to look for some habitat associations by hovering over ‘Show rivers’, ‘Show woodland’ or ‘Show urbanisation’.
  6. Going back to the Species Index on the menu allows you to search for another species.

From any of the species maps it is possible to ‘drill down’ to get a list of species recorded in a specific tetrad. Hovering over a tetrad gives its 10km reference and a name, usually the most significant feature within the tetrad.

 

To draw up a species list for a tetrad:

  1. From any map click on the tetrad of interest. This will bring up the list of species; symbols indicate the species recorded for the relevant winter or summer or breeding period. The padlock symbol indicates a rare or sensitive species that has been mapped at hectad level. It  is possible to switch between the maps from the menu. Hovering over the symbols will indicate the relevant numbers.
  2. The menu also shows the adjacent tetrads. Clicking on one of these will draw up the species list for that square.
  3. It is possible to view the square in a map context by opening the Ordnance Survey box in the left hand menu. It is also possible to zoom out the map to view the surrounding area.
  4. From the tetrad species list it is possible to switch back to a species map by clicking on that species.

 

Supplementary Maps

Species Richness maps have been calculated for both summer and winter periods. These show the county ‘hotspots’; tetrads where most species have been recorded.

  1. From the Atlas home page click on Winter Species Richness or Summer Species Richness from the menu.
  2. The map shows the number of species recorded on an increasing grey scale to black. Hovering over a tetrad gives its name and the number of species recorded.
  3. Click on the tetrad to draw up the species list for that tetrad.

 

Status and Species Accounts

This is work in progress and in many cases has yet to be written. When extracted the UK status and population trends are indicated on the map. On the left hand menu is a link to the species on the BTO Bird Trends website if available and a link to the species account. 

The Species Accounts

Species accounts try to interpret the map data and put it in a wider context.It was decided to try and limit the species accounts to about 1000 words with varying degrees of success. The accounts have been written by a variety of authors following guidelines to ensure a similar format;

Status

General Description/Natural History

World, European and UK status

County History

Present status

Movements, anecdotes etc.

Summary and conclusion.

Status

The comments have a chequered history and have been difficult to quantify. For the Atlas it was decided to adopt McCartney’s definitions of population based on the words ‘common’ and ‘rare’ using the terms: very common, common, fairly common, uncommon, fairly rare, rare and very rare. The populations are spread from >100 000 individuals for very common to less than one annually for very rare. Bands are based on an exponential scale.

 

Term

Non breeding individuals

Breeding Pairs

Very Common

>100,000

>50,000

Common

10,001 – 100,000

5001 – 50,000

Fairly common

1001 – 10,000

501 - 5000

Uncommon

101 - 1000

51 - 500

Fairly Rare

11 - 100

6 - 50

Rare

1 - 10

<5

Very rare

Less than 1 annually

Less than annual

 

Whilst the terms sometimes do not fit easily into current day usage because of the broad range, it was felt that consistency of use was more important and so long as the context in which the terms are used is understood, the exact words are less important. 

McCartney has also provided the definitions adopted for the distribution of ‘terrestrial’ species. (A ‘square’ must have some of its area above MHW).

Present in more than 8/9 (24/27) of squares                                       Very widespread

Present in more than 2/3 (18/27) to 8/9 of squares                          Widespread

Present in more than 4/9 (12/27) to 2/3 of squares                          Fairly widespread

Present in more than 2/9 (6/27) to 4/9 of squares                             Fairly Local

Present in more than 1/27 to 2/9 of squares                                     Local

Present in 1/27 of squares or less                                                    Very Local

 

For Cornwall this means:

Present in more than 935 tetrads                                          Very widespread

Present in more than 701 to 935 tetrads                                Widespread

Present in more than 467 to 701 tetrads                                Fairly widespread

Present in more than 233 to 467 tetrads                                Fairly Local

Present in more than 38 to 233 tetrads                                  Local

Present in 38 tetrads or less                                                 Very Local

General Description and Natural History

This was left very much to the authors to use their discretion to provide an introduction to the species.

World, European and UK Status

Information was taken from the BTO Birdfacts website http://www.bto.org/about-birds/birdfacts  and associated links eg http://www.bto.org/about-birds/birdtrends/2012.

County History

This is based on information from a variety of publications; the main ones being

Rodd E A (1880, Harting J E ed), The Birds of Cornwall and the Isles of Scilly

Penhallurick R D (1978) The Birds of Cornwall and the Isles of Scilly

CBWPS (1931-2007 various eds) Birds in Cornwall, (the Cornwall Bird Report).

Plus additional information from specific reports and publications.

It should be noted that comparisons between The Atlas of Breeding Birds of Britain and Ireland (1968) and the New Atlas of Breeding Birds 1998-91 should be treated with caution. This is because of differences in the recording methodology and coverage of the county. McCartney has provided the following explanation.

Firstly, while it would appear (from Penhallurick 1978) that 63 10-km squares were surveyed for the first Breeding Atlas in 1968-72, that was not the case for the New Atlas in 1988-91. It is apparent that, SW81, SX03, and SX14, were not surveyed, because there are no species records for them at all; and SW44, SW65, SW82, SX09, SS10 and SS11 hold so few records that for all intents and purposes they were not surveyed either. Generally speaking, it appears that only a few seabirds (Fulmar, Shag, Herring Gull, Guillemot, Razorbill and Puffin) were mapped (though Lesser Whitethroat was recorded in SW44). Accordingly, only 54 10-km squares were covered for what might be termed terrestrial species in Cornwall for the New Atlas in 1988-91.

The term ‘core’ tetrads this gets around the differences in recording methods and that some hectads were not surveyed for the majority of species in 88-91. By using a set of ‘core’ hectads (ignoring SW44, SW65, SW81, SW82, SX03, SX09, SX14, SS10 and SS11), comparisons between the two suveys can be made for the 54 hectads in 1988-91. Following that method of comparison, yellowhammers for example were recorded in 54 core hectads in the first national atlas, 51 in the second and 53 in the tetrad atlas.It illustrates the fact that while there have been undoubted Yellowhammer population declines and while there have been local contractions in the distribution, there is no clear evidence of a change in distribution at the hectad level between 1968-72 and 2000-09.

Present Status

This is based on the authors’ interpretation of the patterns of distribution and abundance maps and are often subjective based on the experience of the author of each text. In many cases the accounts have been checked, but unless supportive evidence is provided, such as reference to other research, then these interpretations must be considered only hypothetical.

Apart from seabirds, population estimates have been calculated by McCartney using a suite of methods.

In addition, although all parts of North Cornwall were covered during the Atlas there is some evidence of under recording in winter when species are not singing and dispersed away from territories. This may have a bearing on some of the distribution and abundance maps.

Movements

Ringing recovery data has been used to illustrate movements to and from the county. This is not  a comprehensive list of all recoveries unless stated as such.