Nests are structures built to support and protect eggs and/or offspring from predators, parasites, and adverse weather conditions. Nests are mainly constructed prior to egg laying, meaning that parent birds must make decisions about nest site choice and nest building behavior before the start of egg-laying. Parent birds should be selected to choose nest sites and to build optimally sized nests, yet our current understanding of clutch size-nest size relationships is limited to small-scale studies performed over short time periods. Here, we quantified the relationship between clutch size and nest size, using an exhaustive database of 116 slope estimates based on 17,472 nests of 21 species of hole and non-hole-nesting birds. There was a significant, positive relationship between clutch size and the base area of the nest box or the nest, and this relationship did not differ significantly between open nesting and hole-nesting species. The slope of the relationship showed significant intraspecific and interspecific heterogeneity among four species of secondary hole-nesting species, but also among all 116 slope estimates. The estimated relationship between clutch size and nest box base area in study sites with more than a single size of nest box was not significantly different from the relationship using studies with only a single size of nest box. The slope of the relationship between clutch size and nest base area in different species of birds was significantly negatively related to minimum base area, and less so to maximum base area in a given study. These findings are consistent with the hypothesis that bird species have a general reaction norm reflecting the relationship between nest size and clutch size. Further, they suggest that scientists may influence the clutch size decisions of hole-nesting birds through the provisioning of nest boxes of varying sizes.

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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.

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We examined the effects of different intensities of forest management practices on bird communities in the Bialowieza Forest, eastern Poland. Stands managed for more than 100 years (cutting, planting, removal of dead wood) and stands that were partially protected in nature reserves (sporadic sanitary cutting, removal of dead wood until 2008) were compared with unmanaged stands in the Bialowieza National Park by surveying the bird community during three breeding seasons (2010-2012). Surveys were conducted within three forest habitats: spruce-pine (Pino-Quercetum), lime-hornbeam (Tilio-Carpinetum) and ash-alder (Fraxino-Alnetum). Results showed that habitat structure significantly affected the avian community. The basal area of live trees had a positive effect on abundance of birds, while the density of live trees had negative significant effect on bird abundance and species diversity. We also found significantly lower abundance of insectivorous birds and cavity-nesters in managed compared with unmanaged stands. Birds' assembly in the spruce-pine and ash-alder stands were most sensitive to management. These results show that management can be used to sustain bird communities, including species of conservation concern.

We analyze the frequency of occurrence of small mammals recorded in natural cavities and nest boxes in the Białowieża Forest (eastern Poland) and also describe some parameters of tree cavities. A total of 748 cavities and 60 nest boxes in primeval tree stands and 190 nest boxes in managed tree stands were monitored. Both cavities and nest boxes in primeval stands were occupied by mammals less often than nest boxes in managed stands (0.70%, 0.12%, and 1.26%, respectively). The following mammal species were recorded in natural cavities: Eurasian red squirrel (Sciurus vulgaris L., 1758), forest dormouse (Dryomys nitedula (Pallas, 1778)), yellow-necked mouse (Apodemus flavicollis (Melchior, 1834)), and bats (Microchiroptera species). Three mammalian species were recorded in nest boxes: forest dormouse, fat dormouse (Myoxus glis (L., 1766)), and yellow-necked mouse. The attractiveness of the boxes for mammals increases in managed forests, probably because of a shortage of natural cavities. We suggest that the role of rodents in the breeding ecology of cavity-nesters is underestimated, since studies on natural cavities are rather rare and the species identities of nest predators are most likely poorly recognized. To understand the breeding ecology of birds, ornithologists should study the population dynamics of mammals and the manner in which they use tree cavities and nest boxes.Résumé : Nous analysons la fréquence des petits mammifères retrouvés dans des cavités naturelles et des boîtes de nidification dans la forêt de Białowieźa (Pologne orientale) et nous décrivons certaines des caractéristiques des cavités dans les arbres. Nous avons suivi un total de 748 cavités et 60 boîtes de nidification dans les peuplements forestiers anciens et 190 boîtes de nidification dans les peuplements aménagés. Tant les cavités que les boîtes de nidification des peuplements anciens sont moins fréquemment utilisées par les mammifères que les boîtes de nidification dans les peuplements aménagés (respectivement 0,70 %, 0,12 % et 1,26 %). Les mammifères suivants se retrouvent dans les cavités naturelles : l'écureuil roux (Sciurus vulgaris L., 1758), le lérotin (Dryomys nitedula (Pallas, 1778)), le mulot à collier roux (Apodemus flavicollis (Melchior, 1834)) et des espèces de chauves-souris microchiroptères. Trois espèces de mammifères s'observent dans les boîtes de nidification : le lérotin, le loir gris (Myoxus glis (L., 1766)) et le mulot à collier roux. Dans les forêts aménagées, l'attrait des boîtes augmente chez les mammifères probablement à cause de la pénurie de cavités naturelles. Nous croyons que le rôle des rongeurs dans l'écologie de la reproduction des animaux qui nichent dans les cavités est sous-estimé, car il y a peu d'études sur les cavités naturelles et l'identité des prédateurs des nids est vraisemblablement mal connue. Afin de comprendre l'écologie de la reproduction des oiseaux, les ornithologues devraient étudier la dynamique des mammifères et leur façon d'utiliser les cavités des arbres et les boîtes de nidification....

Summary Secondary hole‐nesting birds that do not construct nest holes themselves and hence regularly breed in nest boxes constitute important model systems for field studies in many biological disciplines with hundreds of scientists and amateurs involved. Those research groups are spread over wide geographic areas that experience considerable variation in environmental conditions, and researchers provide nest boxes of varying designs that may inadvertently introduce spatial and temporal variation in reproductive parameters. We quantified the relationship between mean clutch size and nest box size and material after controlling for a range of environmental variables in four of the most widely used model species in the Western Palaearctic: great tit Parus major, blue tit Cyanistes caeruleus, pied flycatcher Ficedula hypoleuca and collared flycatcher F. albicollis from 365 populations and 79 610 clutches. Nest floor area and nest box material varied non‐randomly across latitudes and longitudes, showing that scientists did not adopt a random box design. Clutch size increased with nest floor area in great tits, but not in blue tits and flycatchers. Clutch size of blue tits was larger in wooden than in concrete nest boxes. These findings demonstrate that the size of nest boxes and material used to construct nest boxes can differentially affect clutch size in different species. The findings also suggest that the nest box design may affect not only focal species, but also indirectly other species through the effects of nest box design on productivity and therefore potentially population density and hence interspecific competition.