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Factors affecting the survival of
Birds of Conservation Concern
by David Leech |
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5. Factors influencing survival rates |
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| The results of a number of previous studies (Thomson et al.,
1997; Siriwardena et al., 1998, 1999; Peach et al.,
1999; Freeman and Crick, 2002) suggest that declining survival rates
may be responsible for the decline in population sizes of many UK
bird species. By correlating survival rates with a range of environmental
variables it may be possible to identify the specific factors involved
in this decline. |
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| Birds are highly mobile and can utilise resources distributed
over large areas. It may therefore be necessary to investigate potential
causes of population declines at relatively large spatial scales to
ensure that the influence of these factors over the entire range of
the population is considered. Both natural
and human-related factors have the
potential to influence survival rates. Table 5.1 illustrates the range
of factors responsible for the mortality of individuals of 12 species
of conservation concern. |
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| Table 5.1. Recovery circumstances where cause
of mortality is known for 12 bird species of conservation concern
(Wernham et al., 2002). The majority of 'Human-related' mortality
was caused by collisions with cars or buildings. The "Predated"
category includes birds taken by both domestic and natural predators.
Recoveries indicated below are likely to be biased towards those individuals
that were deliberately taken, those that died due to human-related
factors and those that were killed by domestic predators, as the remains
of these birds are more likely to be discovered and reported. |
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Species
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Recovery
circumstance
(% recoveries where cause of mortality known)
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| Barnacle goose |
85 |
4 |
- |
11 |
| Hen harrier |
22 |
36 |
- |
42 |
| Grey partridge |
66 |
24 |
5 |
5 |
| Turtle dove |
90 |
4 |
- |
6 |
| Skylark |
- |
23 |
26 |
51 |
| Song thrush |
12 |
45 |
26 |
17 |
| Spotted flycatcher |
37 |
37 |
17 |
9 |
| Tree sparrow |
- |
41 |
44 |
15 |
| Bullfinch |
22 |
39 |
30 |
9 |
| Linnet |
44 |
32 |
13 |
11 |
| Corn bunting |
- |
43 |
43 |
14 |
| Reed bunting |
34 |
41 |
8 |
17 |
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