Abstract
The increase in size of human populations in urban and agricultural areas has resulted in considerable habitat conversion globally. Such anthropogenic areas have specific environmental characteristics, which influence the physiology, life history, and population dynamics of plants and animals. For example, the date of bud burst is advanced in urban compared to nearby natural areas. In some birds, breeding success is determined by synchrony between timing of breeding and peak food abundance. Pertinently, caterpillars are an important food source for the nestlings of many bird species, and their abundance is influenced by environmental factors such as temperature and date of bud burst. Higher temperatures and advanced date of bud burst in urban areas could advance peak caterpillar abundance and thus affect breeding phenology of birds. In order to test whether laying date advance and clutch sizes decrease with the intensity of urbanization, we analyzed the timing of breeding and clutch size in relation to intensity of urbanization as a measure of human impact in 199 nest box plots across Europe, North Africa, and the Middle East (i.e., the Western Palearctic) for four species of hole‐nesters: blue tits (Cyanistes caeruleus), great tits (Parus major), collared flycatchers (Ficedula albicollis), and pied flycatchers (Ficedula hypoleuca). Meanwhile, we estimated the intensity of urbanization as the density of buildings surrounding study plots measured on orthophotographs. For the four study species, the intensity of urbanization was not correlated with laying date. Clutch size in blue and great tits does not seem affected by the intensity of urbanization, while in collared and pied flycatchers it decreased with increasing intensity of urbanization. This is the first large‐scale study showing a species‐specific major correlation between intensity of urbanization and the ecology of breeding. The underlying mechanisms for the relationships between life history and urbanization remain to be determined. We propose that effects of food abundance or quality, temperature, noise, pollution, or disturbance by humans may on their own or in combination affect laying date and/or clutch size.
Highlights
The apparent dichotomy between urban and rural areas is usually used to analyze the impact of urban habitats on populations, this definition does not consider that rural areas may be urbanized when compared to truly natural habitats
In great tits, laying date varied with study plot coordinates, and it differed among habitats (Table 1)
In pied flycatchers, laying date varied with study plot coordinates and was earlier in wooden nest boxes compared to concrete boxes (Table 1)
Summary
The apparent dichotomy between urban and rural areas is usually used to analyze the impact of urban habitats on populations, this definition does not consider that rural areas may be urbanized when compared to truly natural habitats. Urbanized areas influence climate and soil characteristics with impacts on ecosystems (Pickett et al 2011). Temperatures are generally higher in cities than in neighboring rural or natural areas, phenomenon known as “heat island effect” (Escourrou 1990; Pachauri and Reisinger 2008; Stocker et al 2013). These temperature increases are influenced by urban human population density (Gaston 2010; Pickett et al 2011; Susca et al 2011). High human population density causes socio-politico-economic pressures on ecosystems that provide services such as food, raw materials, recreational values and decontaminated water and atmosphere for human populations (Grimm et al 2008; Gaston 2010; Pickett et al 2011), urban areas support animal and plant species (Aronson et al 2014)
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