Esperanza S. Ferrer

Prey Choice, Provisioning Behaviour, and Effects of Early Nutrition on Nestling Phenotype of Titmice

Abstract: It is generally assumed that blue and great tits (Cyanistes caeruleus, Parus major) compete for the same type of food (Lepidoptera larvae) during the breeding season and that the former have some advantage because they are usually earlier and can exploit small caterpillars that are often more abundant and are not consumed by great tits. However, it is not clear whether, when confronted with similar circumstances (e.g., nestling demand), blue and great tits show similar preferences for a particular caterpillar type. In this 2-y study, we compare the diet of both tit species in detail by controlling for hatching date and brood size. We also examine how the contribution of caterpillars and spiders to the diet is related to nestling development. A positive relationship was found between the percentage of spiders in the diet and nestling tarsus length in both species, reinforcing the idea that neonatal nutrition could have a strong influence on nestling phenotype (e.g., offspring size). Such a correlation may arise because spiders contain a high level of taurine, an essential nutrient in the early development of young, and/or this prey type contains more calcium than other food items, which may affect the rate of nestling bone mineralization. Blue tits fed their young double the number of tortricid larvae in comparison with great tits, whereas the latter showed a clear preference for noctuids and exploited, with a low frequency, a type of larvae not consumed by blue tits, hairy caterpillars (Lasiocampidae). Our results point to resource partitioning by these species in this forest ecosystem and contribute to a better understanding of feeding ecology of titmice, which is particularly timely in a global warming context.

Genetic structure reflects natal dispersal movements at different spatial scales in the blue tit, Cyanistes caeruleus

The study of the genetic consequences of dispersal is a central topic in evolutionary, conservation and behavioural research. However, few studies have simultaneously considered dispersal movements from marked individuals and contemporary patterns of gene flow. We analysed the link between dispersal behaviour and gene flow in four populations of blue tits with different degrees of connectivity. For this purpose, we monitored four breeding patches and used genotypic and captureemarkerecapture data to study the genetic consequences of dispersal at different spatial scales. Data on natal dispersal movements revealed that both males and females dispersed less than expected under a random pattern of settlement at the two large spatial scales considered: the whole study area and the two main localities. However, natal dispersal distance was lower than expected under random settlement within natal patches in males whereas an opposite pattern was found for females. Accordingly, microsatellite data revealed limited gene flow between the localities studied and an isolation-by-distance pattern of genetic structure that was particularly strong at the large spatial scale (i.e. considering geographically distant breeding patches). Finally, the strong male philopatry was reflected by a stronger genetic structure and a lower admixed ancestry in this sex. Overall, we found evidence that restricted dispersal and fragmentation may have both contributed to reduce interpopulation gene flow at different spatial scales in a forest species and that there is concordance between genetic studies and those based on captureemarkerecapture.

Heterozygosity at a single locus explains a large proportion of variation in two fitness-related traits in great tits: a general or a local effect?

In natural populations, mating between relatives can have important fitness consequences due to the negative effects of reduced heterozygosity. Parental level of inbreeding or heterozygosity has been also found to influence the performance of offspring, via direct and indirect parental effects that are independent of the progeny own level of genetic diversity. In this study, we first analysed the effects of parental heterozygosity and relatedness (i.e. an estimate of offspring genetic diversity) on four traits related to offspring viability in great tits (Parus major) using 15 microsatellite markers. Second, we tested whether significant heterozygosity–fitness correlations (HFCs) were due to ‘local’ (i.e. linkage to genes influencing fitness) and/or ‘general’ (genome‐wide heterozygosity) effects. We found a significant negative relationship between parental genetic relatedness and hatching success, and maternal heterozygosity was positively associated with offspring body size. The characteristics of the studied populations (recent admixture, polygynous matings) together with the fact that we found evidence for identity disequilibrium across our set of neutral markers suggest that HFCs may have resulted from genome‐wide inbreeding depression. However, one locus (Ase18) had disproportionately large effects on the observed HFCs: heterozygosity at this locus had significant positive effects on hatching success and offspring size. It suggests that this marker may lie near to a functional locus under selection (i.e. a local effect) or, alternatively, heterozygosity at this locus might be correlated to heterozygosity across the genome due to the extensive ID found in our populations (i.e. a general effect). Collectively, our results lend support to both the general and local effect hypotheses and reinforce the view that HFCs lie on a continuum from inbreeding depression to those strictly due to linkage between marker loci and genes under selection.

Spatiotemporal and genetic contingency of extrapair behaviour in a songbird

Multiple mating to obtain genetic benefits has been championed as the most likely cause of the evolution of polygamy. However, this assumption has been put into question by an increasing number of recent studies, most of which highlight the importance of considering ecological constraints to comprehend variation in extrapair (EP) behaviour. Here, we studied patterns of extrapair paternity (EPP) in the great tit, Parus major, using data from 11 nestbox plots that differed in population size and breeding conditions. Specifically, we analysed EPP rates in relation to socioecological variables that could influence the way individuals encountered one another in space and time, we tested whether adults engaged in EPP with more heterozygous, more compatible or phenotypically superior individuals than their social mates and we analysed whether extrapair offspring (EPO) were phenotypically or genetically superior to within-pair offspring. Our results do not provide support for the genetic benefit hypothesis from either the male or the female perspective. EPO were heavier than their within-pair paternal half-siblings, but there was no significant difference between EPO and their within-pair maternal half-siblings in terms of phenotypic quality. Regarding socioecological factors, we found a negative relationship between breeding synchrony and EPP rates both within and among plots, which suggests that males face a trade-off between mate guarding and obtaining EPP elsewhere. Our results show that most males engaged in EPP after the fertile period of their social female despite having to travel long distances: about half of the detected cases of EPP involved individuals from different woodlands. This study indicates that when and where to engage in EPP seem to be more relevant factors than with whom to do it and highlights the importance of considering spatiotemporal constraints at a landscape scale to achieve a better understanding of variation in EP mating behaviour.

Mating strategies, parental investment and mutual ornamentation in Iberian Rock Sparrows (Petronia petronia)

Relatively few bird species show complex social mating systems whose preponderance in a population is likely to affect the patterns of parental care observed there. In turn, parental investment is likely to be related to the expression of certain ornaments, which may reveal information on the bearer’s individual quality. Here we address both issues in a species characterised by several forms of parental care (both biparental and uniparental care) and in which both sexes possess a yellow breast patch, the rock sparrow (Petronia petronia). In our population, males contributed more to the care of the young in comparison with other populations. Social monogamy was the most frequent mating pattern and the percentage of cases of female (or male) brood desertion was lower with respect to that reported in previous studies, suggesting a flexible behaviour of this species to deal with different social environments. Birds did not pair assortatively with respect to the size of the yellow breast patch and we found no significant relationship between this trait and the frequency with which parents provisioned their chicks. However, we observed a positive relationship between male yellow patch size and nestling tarsus length, which suggests that more ornamented males are better parents. Males, but not females, differentially allocated parental investment in response to female ornamentation, although the benefits that males may gain from choosing more attractive females remain unidentified. Our results on paternal care investment along with previous studies on this species, reinforcing the view that the rock sparrow constitutes a good model to study sexual conflict over parental care under different social environments.

Effect of nestbox type on the breeding performance of two secondary hole-nesting passerines

The use of nestboxes to study secondary cavity nesting avian species has greatly improved the knowledge related to many fields of environmental sciences. The aim of this study has been to compare the breeding performance of Great Tits (Parus major) and Blue Tits (Cyanistes caeruleus) in two types of nestboxes that differ with regard to their shape and thermal properties. Both nestbox types were placed in the same area to avoid confounding factors. There were significant differences between the extreme values of temperature and relative humidity obtained for the two nestbox types, and this was also the case in their daily patterns. Secondary hole-nesting birds appear to prefer breeding in woodcrete nestboxes. Nest predation was, however, significantly greater in woodcrete nestboxes. The nest height was significantly higher in woodcrete nestboxes, as was the danger distance between the nest cup and the entrance hole, which could account for the fact that Great Tits prefer this type of nestbox. The laying date was earlier in woodcrete boxes, but nestbox type did not influence clutch size. However, the eggs of both species were significantly smaller in woodcrete boxes. Breeding success was worse in woodcrete nestboxes. Nestbox type also affected the incubation pattern in both species, and attentiveness was significantly diminished in woodcrete nestboxes. This study reinforces the idea that the type of nestbox used in avian studies is not a trivial issue and may have strong biological effects on avian populations. It is important to take this into account when nestboxes are used as management measures for bird conservation.ZusammenfassungAuswirkungen des Nistkastentyps auf die Brutleistung der sekundären Höhlenbrüter Kohlmeise und BlaumeiseDie Benutzung von Nistkästen für Studien über sekundäre Höhlenbrüter hat zur Weiterentwicklung vieler Bereiche der Biowissenschaften beigetragen. Das Ziel der vorliegenden Studie war der Vergleich der Brutleistung der Kohlmeise (Parus major) und der Blaumeise (Cyanistes caeruleus) in zwei Nistkastentypen mit unterschiedlicher Form und thermischen Eigenschaften. Beide Nistkastentypen wurden in derselben Gegend positioniert, um verfälschende Faktoren zu vermeiden. Es wurden signifikante Unterschiede zwischen den maximalen und minimalen Temperaturen sowie zwischen der relativen Luftfeuchtigkeit gemessen, und dies betraf auch deren Tageschwankungen. Beide Arten bevorzugten die Holzbetonnistkästen. Nestraub war aber signifikant höher in den Holzbetonkästen. Die Nesthöhe war in Holzbetonkästen signifikant größer, ebenso die Distanz zwischen Eingang und das Nest. Dies könnte einer der Gründe sein, dass Kohlmeisen diesen Typ von Nistkasten präferieren. Der Legebeginn war in Holzbetonkästen früher; der Nistkastentyp hatte aber keinen Einfluss auf die Gelegegröße. Allerdings waren die Eier beider Arten in den Holzbetonkästen signifikant kleiner und der Bruterfolg war geringer in den Holzbetonkästen. Der Nistkastentyp beeinflusste auch das Bebrütungsmuster beider Arten und die Aufmerksamkeit der Brutvögel am Nest war geringer bei Holzbetonkästen. Diese Studie unterstützt die Annahme, dass der Typ des Nistkastens keine triviale Rolle in ornithologischen Studien spielt und große biologische Einflüsse haben kann. Dies ist zu berücksichtigen, wenn Nistkästen im Vogelschutz eingesetzt werden.

Habitat structure influences the song characteristics within a population of Great Tits Parus major

ABSTRACT Capsule: The structure of Great Tit Parus major songs is shaped by the acoustic properties of the habitat within the breeding territory of individuals. Aim: To test whether the structure of the habitat influences song structure within a population of Great Tits P. major. Methods: We recorded Great Tit songs from 42 territories on two different days and measured the habitat structure in each territory. We also trapped the males and estimated the breeding density around each territory, so were able to control the analysis by date, breeding density and male characteristics. Results: Song pause length was positively affected by the ground cover, while the song rate and the minimum frequency were negatively affected by the shrub cover. Male size negatively affected the peak frequency of the songs, whereas the age of the males affected the frequency range; older males sang with a broader bandwidth. Conclusion: This study suggests that Great Tits are capable of adjusting their vocalizations in each territory, presumably to enhance transmission owing to vocal plasticity.