Virginie Demeyrier

Variation in clutch size in relation to nest size in birds

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.

Urbanization Is Associated with Divergence in Pace-of-Life in Great Tits

As an extension of the classic life history theory, the recently highlighted pace-of-life syndrome hypothesis predicts the coevolution of behavioural, physiological and life-history traits. For instance, bolder and shyer individuals do not only differ in personality profiles, but also in neuro-endocrinology and breeding patterns. While theory predicts that bolder (i.e. proactive), more aggressive individuals should colonize more rapidly urbanized habitats than shyer (i.e. reactive), less aggressive individuals, it is also predicted that across generations, adaptive selection processes could favour shyer individuals that are more sensitive to novel environmental cues. Here we compared two personality traits (handling aggression, exploration score in a novel environment), one physiological trait related to stress response (breath rate) and four breeding traits (lay date, clutch size, hatching success and fledging success) in a rural and an urban study population of Mediterranean great tits Parus major. Mixed models revealed strong phenotypic divergence between forest and city in most traits explored, in particular in personality, whereby urban great tits were more reactive to stress and faster explorers compared to rural birds (yet not more aggressive). Urban birds also laid smaller broods earlier in spring compared to their rural conspecifics, and city broods resulted in lower hatching success yet interestingly fledging success was similar. Nest-box centered measures of anthropogenic (artificial light, pedestrians and cars) perturbation and resource abundance allowed us to go beyond the classical forest/city comparison by exploring the phenotypic variation across an urbanization gradient. This revealed that high urbanisation in nest-box surroundings was associated overall with earlier breeding and smaller clutches, but also with faster breath rate, although these trends showed strong annual variation. Ongoing rapid urbanization and non-random gene flow between rural and urban great tits could both contribute to the high prevalence of bold breeders in the city. Our study suggests the existence of urban and rural great tit ecotypes with different pace-of-life, but also a finer-scale divergence along the degree of urbanisation within the city. Future studies are required to determine whether this phenotypic variation at different spatiotemporal scales is adaptive and whether it has a genetic basis or results from phenotypic plasticity.

Experimental demonstration of an ecological trap for a wild bird in a human-transformed environment

An ecological trap occurs when animals prefer to settle in poor-quality habitats even though alternative high-quality habitats are available. Thus, to find evidence of a trap one must show (1) a habitat preference and (2) a mismatch between the settlement decision and reproduction or survival. However, demonstrations of traps in the wild are currently limited because the misleading cues have to be identified and are usually difficult to manipulate experimentally. Places where humans transform habitats, such as urbanized areas, are particularly prone to this ecological phenomenon. Here we tested whether the size of a human-made structure (artificial cavities) can induce maladaptive breeding responses via an ecological trap mechanism in an urban secondary-cavity nesting bird, the great tit, Parus major. Previous studies showed that great tits prefer to breed in large cavities; cavity size is thus used as a cue in nest site selection. Reproductive investment in great tits has also been shown to be influenced by the breeding cavity size. However, this behaviour can only be adaptive if cavity size matches the quality of the breeding habitat. This is not necessarily the case in urbanized environments where natural habitat has been removed or breeding habitat modified. We performed a cavity choice experiment, providing an opportunity for great tits to choose between three cavity size options, and monitored their subsequent breeding attempts. We found that urban great tits preferred the largest artificial cavities for breeding when they could choose between small, medium-sized and large cavities. Individuals from the largest cavities also invested more in egg production, yet had a lower fledging success than those from medium-sized cavities, experimentally showing a trap mechanism in free-living animals. With this study, we shed light on maladaptation associated with human-transformed habitat.

Interspecific variation in the relationship between clutch size, laying date and intensity of urbanization in four species of hole-nesting birds

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.

Nest size is not closely related to breeding success in Blue Tits: A long-term nest-box study in a Mediterranean oak habitat

ABSTRACT Various components of breeding success are predicted to be related to avian nest size because (1) some individuals are physically able to build larger nests than other individuals or (2) larger nests provide more protection in the absence of predation than smaller nests. The results of an 18-yr correlative nest-box study in Blue Tits (Cyanistes caeruleus) show that nest size is not closely related to components that reflect breeding performance, after controlling for other female characteristics (first-egg date, clutch size, and female age) assumed to influence breeding performance in long-term studies. Our results support those of most short-term field studies that have reported weak associations between nest size and breeding performance in cavity-nesting passerines. We suggest that the absence of an association between nest size and breeding performance can be explained by the fact that the vast majority of nest-box studies have used small nest chambers that imposed physical constraints on the full expression of the nest. We recommend using a larger range of nest-chamber sizes that better reflect the characteristics of natural holes exploited by secondary cavity-nesting species.

Great Tits build shallower nests than Blue Tits

Comparative studies predicted or reported weaker or stronger positive relationships between nest size and body size both within and across avian species. Here we show that in relatively small nest-chambers, larger Great Tits (Parus major) build shallower nests than smaller Blue Tits (Cyanistes caeruleus). Our results from the Mediterranean region support findings from published studies that were conducted at more northerly latitudes (UK and Poland). Potential impacts of the local climate and predation risks on the species-specific expression of the size of fresh nests are discussed.

Urban Great Tits (Parus major) Show Higher Distress Calling and Pecking Rates than Rural Birds across Europe

Environmental change associated with urbanization is considered one of the major threats to biodiversity. Some species nevertheless seem to thrive in the urban areas, probably associated with selection for phenotypes that match urban habitats. Previous research defined different “copying styles” in distress behavior during the handling of birds. These behaviors vary along a continuum from “proactive” to “reactive” copers. By studying avian distress behaviors we aimed to broaden our understanding of the relationship between coping styles and urbanization. Using a large-scale comparative study of seven paired rural and urban sites across Europe, we assayed distress behaviors during handling of urban and rural-dwelling populations of the great tit Parus major. We detected no consistent pairwise differences in breath rate between urban and rural habitats. However, urban great tits displayed more distress calling (fear screams) and higher pecking rate (handling aggression) than rural birds. These findings suggest that urban great tits have a more proactive coping strategy when dealing with stressful conditions. This finding is in line with previous studies implying that urban great tits are more explorative, less neophobic and display shorter flight distances than their rural counterparts, representing further aspects of the same “proactive”, coping strategy. Future research should investigate whether reported differences in distress behavior are due to local adaption caused by natural selection or due to phenotypic plasticity.

Great tits and the city: Distribution of genomic diversity and gene–environment associations along an urbanization gradient

Urbanization is a growing concern challenging the evolutionary potential of wild populations by reducing genetic diversity and imposing new selection regimes affecting many key fitness traits. However, genomic footprints of urbanization have received little attention so far. Using RAD sequencing, we investigated the genomewide effects of urbanization on neutral and adaptive genomic diversity in 140 adult great tits Parus major collected in locations with contrasted urbanization levels (from a natural forest to highly urbanized areas of a city; Montpellier, France). Heterozygosity was slightly lower in the more urbanized sites compared to the more rural ones. Low but significant effect of urbanization on genetic differentiation was found, at the site level but not at the nest level, indicative of the geographic scale of urbanization impact and of the potential for local adaptation despite gene flow. Gene–environment association tests identified numerous SNPs with small association scores to urbanization, distributed across the genome, from which a subset of 97 SNPs explained up to 81% of the variance in urbanization, overall suggesting a polygenic response to selection in the urban environment. These findings open stimulating perspectives for broader applications of high‐resolution genomic tools on other cities and larger sample sizes to investigate the consistency of the effects of urbanization on the spatial distribution of genetic diversity and the polygenic nature of gene–urbanization association.

Disentangling drivers of reproductive performance in urban great tits: a food supplementation experiment

ABSTRACT Worldwide urban expansion induces degradation of the natural environment, resulting in new constraints in terms of breeding sites, anthropogenic disturbances as well as food resources. The alteration of resource abundance and type may induce non-adaptive investments in reproduction from urban dwellers. Food availability and quality have been identified as potential drivers of the decline in passerine body mass and fledging success in urbanized landscapes, particularly if birds misinterpret cues of food abundance used to adjust their reproductive investment. In a previous study, we demonstrated in urban great tits, Parus major, that highly preferred larger cavities have larger clutches with lower breeding success, leading to a maladaptive breeding investment. Previous studies also showed that urban great tits are smaller or thinner than rural ones, both at nestling and adult stages. Here, we present the results of a food-supplementation experiment to examine whether food resources mediate this maladaptive breeding investment and constrain the reproductive performance of this urban bird population. We predicted higher performance in food-supplemented broods, especially in larger cavities, and stronger effects of the supplementation in more artificialized territories. Surprisingly, we found that food-supplemented nestlings and their parents had lower body mass and condition, especially in areas with more pedestrians. Supplementation was also associated with lower nestling survival until fledging in places that presented lower levels of naturalness, independently of cavity size. This work highlights a lack of knowledge on avian feeding behaviour in cities, a key element for understanding how breeding performance is affected by human presence and habitat naturalness. Summary: Food supplementation could have a negative impact on breeding performance of wild urban great tits.

Nest-box size influences where secondary-cavity exploiters roost and nest: a choice experiment

AbstractThe impact of nest-box characteristics (design, position, content) on decisions where to roost or nest have rarely been experimentally investigated. Older studies claimed that secondary cavity-exploiters, such as tits (Paridae), prefer smaller boxes for roosting and larger boxes for breeding. Surprisingly, these aspects of box preference have to our knowledge not been examined in choice experiments. We therefore allowed free-ranging birds to use, as roosting or nesting sites, three box designs attached together on the same support, covering the range of box sizes used to attract Great (Parus major) or Blue (Cyanistes caeruleus) Tits in long-term investigations. We observed that medium-sized and large boxes contained disproportionally more avian excrements before nesting than small boxes. The large boxes also contained disproportionally more body plumages prior to nesting and Great Tit nests. Nest-box size therefore influenced where the birds roosted and nested. Potential costs and benefits of exploitation of boxes differing in size are briefly discussed.ZusammenfassungDie Nistkastengröße beeinflusst, wo Sekundär-Höhlenbrüter schlafen und brüten: ein Wahlexperiment Der Einfluss von Nistkasten-Charakteristika (Design, Lage, Inhalt) auf die Entscheidungen eines Vogels bei der Schlafplatz- und Neststandortswahl wurde bisher kaum experimentell untersucht. Ältere Arbeiten behaupten, dass Sekundär-Höhlenbrüter wie etwas Meisen (Paridae) kleinere Kästen zum Schlafen und größere Kästen für die Brut bevorzugen. Überraschenderweise wurden diese Aspekte der Nistkastenwahl unseres Wissens nach noch nicht in Wahlexperimenten untersucht. Wir gaben daher Wildvögeln die Möglichkeit, drei verschiedene Nistkastenvarianten, die das in Langzeitstudien an Kohl- (Parus major) und Blaumeisen (Cyanistes caeruleus) verwendete Größenspektrum abdeckten, und die wir jeweils zusammen an einer gemeinsamen Halterung anbrachten, zum Schlafen und Nisten zu nutzen. Wir beobachteten, dass mittelgroße und große Nistkästen vor der Brutzeit überproportional mehr Vogelexkremente enthielten als kleine Kästen. In großen Kästen fanden sich darüber hinaus vor der Brutzeit überproportional mehr Körperfedern und Kohlmeisen-Nester. Die Nistkastengröße beeinflusste also die Schlafund Nistplatzwahl der Vögel. Potentielle Kosten und Vorteile einer unterschiedlichen Kastennutzung nach Größe werden kurz diskutiert.