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The Effect of Climate Change on Birds
by David Leech |
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| 4. |
Influence
of climatic change on population size |
4.1 |
Direct effects
of temperature and rainfall |
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| As ambient temperatures fall, the rate
at which heat is lost from the body to the environment increases.
The energetic cost to the individual of maintaining a constant body
temperature is therefore greater at lower temperatures, which may
have unfavourable consequences for body condition and survival.
Heavy rainfall may further increase rates of heat loss in birds,
as their plumage provides less effective insulation when wet. |
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| The results of previous studies suggest
that the survival rates of a wide variety of British bird species
decrease under servere weather conditions during the winter period,
particularly as winters become colder and wetter. |
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- The survival rates of both first-year and adult lapwings (Vanellus
vanellus) decrease as mean winter soil temperatures decrease
(Fig 4.1) (Peach et al., 1994).
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Lapwing survival
rates are reduced during cold winters.
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Fig 4.1. Graph showing
that the survival probability of adult lapwings halves (from 80%
to 40%) as mean air temperature during winter falls from 6°
to O°. (From Peach et al., 1994).
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- Song thrush (Turdus philomelos) survival rates are reduced
during cold winters (Thomson et al., 1997).
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- Treecreeper (Certhia familiaris) survival rates fall
as rainfall during the winter period increases (Peach et al.,
1995).
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Treecreeper mortality
is positively related to the amount of rainfall during the winter
period.
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| Climatic conditions may also directly influence
breeding success. Climatic amelioration over the winter period may
improve the condition of parent birds during the breeding season,
allowing them to increase their level of investment in the offspring
and therefore, potentially, to increase the fledging success of their
brood. Alternatively, increases in temperature during the breeding
season itself may reduce the rate of heat loss experienced by the
offspring, thus increasing their probability of survival. |
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| Mean annual temperatures are predicted to
continue rising over the course of the current century in response
to elevated concentrations of greenhouse gases in the atmosphere (see
Section 2). Subsequent increases in the survival rates and breeding
success of some British bird species might therefore be predicted.
However, other species may suffer a decrease in survival rates over
the winter period due to the predicted increase in the incidence of
heavy rainfall. |
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