Cambridge University Press
978-1-107-07213-8 — Ecology and Conservation of Forest Birds
Edited by Grzegorz Mikusiński , Jean-Michel Roberge , Robert Fuller
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11
Population Trends
and Conservation Status
of Forest Birds
ALEKSI LEHIKOINEN AND
RAIMO VIRKKALA
11.1 Introduction
Bird populations can have large temporal variations both in the short
term, from year to year, and in the long term, producing trends. The
exact reason behind these temporal variations often remains unclear,
although there are several suggestions as to the cause of the temporal
patterns (Wiens 1989; Newton 1998; Eglington & Pearce-Higgins 2012;
Ram et al. 2017).
Environmental variation, such as differences in weather conditions
and food availability, has a profound effect on birds (Newton 1998;
Møller et al. 2010). A high proportion of the bird species in Europe
are migratory, particularly in temperate and boreal areas, so many birds
are affected by environmental variation over extremely large areas of
the planet (Newton 2008). Long-distance migrants that breed in the
Northern Hemisphere meet environmental variation in three areas:
the breeding areas, migratory areas and wintering areas in the tropics.
As a classic example, the numbers of the common whitethroat Sylvia
communis collapsed in Britain in the late 1960s and early 1970s as a
consequence of extreme drought in the Sahel region of Africa, the
main wintering area of the species (Winstanley et al. 1974; Batten &
Marchant 1977). Similarly, in North America, survival and breeding
success of American redstarts Setophaga ruticilla are influenced by cli-
matic conditions in the wintering grounds (Norris et al. 2004; Marra
et al. 2015).
Many of the recent population changes of forest birds are connected
with large-scale habitat alteration caused by human activities (Butchart
et al. 2010; Hoffman et al. 2010) and the effects of climate change (Crick
2004; Gregory et al. 2009; Jiguet et al. 2010). Although climate change
Aleksi Lehikoinen