Interspecific variation in the relationship between clutch size, laying date and intensity of urbanization in four species of hole‐nesting birds
Authors: Vaugoyeau Marie , Adriaensen Frank , Artemyev Alexandr , Bańbura Jerzy , Barba Emilio , Biard Clotilde , Blondel Jacques , Bouslama Zihad , Bouvier Jean‐Charles , Camprodon Jordi , Cecere Francesco , Charmantier Anne , Charter Motti , Cichoń Mariusz , Cusimano Camillo , Czeszczewik Dorota , Demeyrier Virginie , Doligez Blandine , Doutrelant Claire , Dubiec Anna , Eens Marcel , Eeva Tapio , Faivre Bruno , Ferns Peter N. , Forsman Jukka T. , García‐del‐Rey Eduardo , Goldshtein Aya , Goodenough Anne E. , Gosler Andrew G. , Grégoire Arnaud , Gustafsson Lars , Harnist Iga , Hartley Ian R. , Heeb Philipp , Hinsley Shelley A. , Isenmann Paul , Jacob Staffan , Juškaitis Rimvydas , Korpimäki Erkki , Krams Indrikis , Laaksonen Toni , Lambrechts Marcel M. , Leclercq Bernard , Lehikoinen Esa , Loukola Olli , Lundberg Arne , Mainwaring Mark C. , Mänd Raivo , Massa Bruno , Mazgajski Tomasz D. , Merino Santiago , Mitrus Cezary , Mönkkönen Mikko , Morin Xavier , Nager Ruedi G. , Nilsson Jan‐Åke , Nilsson Sven G. , Norte Ana C. , Orell Markku , Perret Philippe , Perrins Christopher M. , Pimentel Carla S. , Pinxten Rianne , Richner Heinz , Robles Hugo , Rytkönen Seppo , Senar Juan Carlos , Seppänen Janne T. , Pascoal da Silva Luis , Slagsvold Tore , Solonen Tapio , Sorace Alberto , Stenning Martyn J. , Tryjanowski Piotr , von Numers Mikael , Walankiewicz Wieslaw , Møller Anders Pape 
Published: July 2016

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.