Raivo Mänd

The design of artificial nestboxes for the study of secondary hole-nesting birds: a review of methodological inconsistencies and potential biases

Abstract. The widespread use of artificial nestboxes has led to significant advances in our knowledge of the ecology, behaviour and physiology of cavity nesting birds, especially small passerines. Nestboxes have made it easier to perform routine monitoring and experimental manipulation of eggs or nestlings, and also repeatedly to capture, identify and manipulate the parents. However, when comparing results across study sites the use of nestboxes may also introduce a potentially significant confounding variable in the form of differences in nestbox design amongst studies, such as their physical dimensions, placement height, and the way in which they are constructed and maintained. However, the use of nestboxes may also introduce an unconsidered and potentially significant confounding variable due to differences in nestbox design amongst studies, such as their physical dimensions, placement height, and the way in which they are constructed and maintained. Here we review to what extent the characteristics of artificial nestboxes (e.g. size, shape, construction material, colour) are documented in the ‘methods’ sections of publications involving hole-nesting passerine birds using natural or excavated cavities or artificial nestboxes for reproduction and roosting. Despite explicit previous recommendations that authors describe in detail the characteristics of the nestboxes used, we found that the description of nestbox characteristics in most recent publications remains poor and insufficient. We therefore list the types of descriptive data that should be included in the methods sections of relevant manuscripts and justify this by discussing how variation in nestbox characteristics can affect or confound conclusions from nestbox studies. We also propose several recommendations to improve the reliability and usefulness of research based on long-term studies of any secondary hole-nesting species using artificial nestboxes for breeding or roosting.

Sexual selection for white tail spots in the barn swallow in relation to habitat choice by feather lice

Many bird species have white spots in their tails or wing feathers, and such characters have been hypothesized to be either reliable signals (handicaps) or amplifiers that facilitate the message of a signal. In barn swallows, Hirundo rustica, the size of the white spots in the tail feathers is sexually dimorphic and positively correlated with feather length. We tested whether such spots act as handicaps or amplifiers. These white spots affect sexual selection in barn swallows, as shown by an experiment in which we randomly subjected males to (1) a considerable reduction of the size of all the spots by the use of a black permanent marker pen, (2) a small reduction of the size of the spots, or (3) no reduction. There was a positive association between spot size and the number of offspring produced per season. The white tail spots were preferred by feather-eating Mallophaga as a feeding site: holes made by Mallophaga were more abundant in the white spots than expected by chance. A habitat choice experiment with Mallophaga on barn swallow tail feathers revealed that they preferred white spots over black parts of the tail feathers. We therefore expected long-tailed male barn swallows to have more Mallophaga than short-tailed males. However, the opposite relationship was observed, indicating that long-tailed males may reliably signal their quality by the presence of large white tail spots without parasite damage. Thus white tail spots in barn swallows appear to be a reliable signal of phenotypic quality. Copyright 1999 The Association for the Study of Animal Behaviour.

Providing nest boxes for hole-nesting birds – Does habitat matter?

Nest boxes are a popular management tool to increase nest site availability for hole-nesting birds, but biological consequences of this technique in different habitats are poorly studied. In our study area in southwestern Estonia, nest boxes for small passerines were set up in deciduous and coniferous woods. Great tits Parus major preferred the food-rich deciduous habitat for breeding, as judged by higher nest-box occupation, earlier egg-laying and larger clutches and eggs. However, in coniferous habitat more and heavier young fledged per nest, and the return rate of both fledglings and adults was higher. We propose two mutually non-exclusive explanations, both related to the maladaptive outcome of the provision of nest boxes: (i) in the preferred habitat, nest boxes caused a supra-optimal breeding density leading to an ecological trap; (ii) boxes drastically improved the non-preferred habitat, but birds were unable to exploit the breeding habitat fully. One should be careful in providing large numbers of artificial nest sites in preferred habitats. Sometimes it would be more preferable to improve less favourable habitats by removing critical constraints.

Geographical variation in egg mass and egg content in a passerine bird.

Reproductive, phenotypic and life-history traits in many animal and plant taxa show geographic variation, indicating spatial variation in selection regimes. Maternal deposition to avian eggs, such as hormones, antibodies and antioxidants, critically affect development of the offspring, with long-lasting effects on the phenotype and fitness. Little is however known about large-scale geographical patterns of variation in maternal deposition to eggs. We studied geographical variation in egg components of a passerine bird, the pied flycatcher (Ficedula hypoleuca), by collecting samples from 16 populations and measuring egg and yolk mass, albumen lysozyme activity, yolk immunoglobulins, yolk androgens and yolk total carotenoids. We found significant variation among populations in most egg components, but ca. 90% of the variation was among individuals within populations. Population however explained 40% of the variation in carotenoid levels. In contrast to our hypothesis, we found geographical trends only in carotenoids, but not in any of the other egg components. Our results thus suggest high within-population variation and leave little scope for local adaptation and genetic differentiation in deposition of different egg components. The role of these maternally-derived resources in evolutionary change should be further investigated.

Climate change, breeding date and nestling diet: how temperature differentially affects seasonal changes in pied flycatcher diet depending on habitat variation

1. Climate warming has led to shifts in the seasonal timing of species. These shifts can differ across trophic levels, and as a result, predator phenology can get out of synchrony with prey phenology. This can have major consequences for predators such as population declines owing to low reproductive success. However, such trophic interactions are likely to differ between habitats, resulting in differential susceptibility of populations to increases in spring temperatures. A mismatch between breeding phenology and food abundance might be mitigated by dietary changes, but few studies have investigated this phenomenon. Here, we present data on nestling diets of nine different populations of pied flycatchers Ficedula hypoleuca, across their breeding range. This species has been shown to adjust its breeding phenology to local climate change, but sometimes insufficiently relative to the phenology of their presumed major prey: Lepidoptera larvae. In spring, such larvae have a pronounced peak in oak habitats, but to a much lesser extent in coniferous and other deciduous habitats. 2. We found strong seasonal declines in the proportions of caterpillars in the diet only for oak habitats, and not for the other forest types. The seasonal decline in oak habitats was most strongly observed in warmer years, indicating that potential mismatches were stronger in warmer years. However, in coniferous and other habitats, no such effect of spring temperature was found. 3. Chicks reached somewhat higher weights in broods provided with higher proportions of caterpillars, supporting the notion that caterpillars are an important food source and that the temporal match with the caterpillar peak may represent an important component of reproductive success. 4. We suggest that pied flycatchers breeding in oak habitats have greater need to adjust timing of breeding to rising spring temperatures, because of the strong seasonality in their food. Such between-habitat differences can have important consequences for population dynamics and should be taken into account in studies on phenotypic plasticity and adaptation to climate change.

Brominated flame retardants and organochlorines in the European environment using great tit eggs as a biomonitoring tool

Large-scale studies are essential to assess the emission patterns and spatial distribution of organohalogenated pollutants (OHPs) in the environment. Bird eggs have several advantages compared to other environmental media which have previously been used to map the distribution of OHPs. In this study, large-scale geographical variation in the occurrence of OHPs, such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and organochlorine pesticides (OCPs), was investigated throughout Europe using eggs of a terrestrial residential passerine species, the great tit (Parus major). Great tit eggs from 22 sampling sites, involving urban, rural and remote areas, in 14 European countries were collected and analysed (5-8 eggs per sampling site). The environmentally most important congeners/compounds of the analysed pollutants were detectable in all sampling locations. For PCBs, PBDEs and OCPs, no clear geographical contamination pattern was found. Sum PCB levels ranged from 143 ng/g lipid weight (lw) to 3660 ng/g lw. As expected, PCB concentrations were significantly higher in the sampled urban compared to the remote locations. However, the urban locations did not show significantly higher concentrations compared to the rural locations. Sum PBDEs ranged from 4.0 ng/g lw to 136 ng/g lw. PBDEs were significantly higher in the urbanized sampling locations compared to the other locations. The significant, positive correlation between PCB and PBDE concentrations suggests similar spatial exposure and/or mechanisms of accumulation. Significantly higher levels of OCPs (sum OCPs ranging from 191 ng/g lw to 7830 ng/g lw) were detected in rural sampling locations. Contamination profiles of PCBs, PBDEs and OCPs differed also among the sampling locations, which may be due to local usage and contamination sources. The higher variance among sampling locations for the PCBs and OCPs, suggests that local contamination sources are more important for the PCBs and OCPs compared to the PBDEs. To our knowledge, this is the first study in which bird eggs were used as a monitoring tool for OHPs on such a large geographical scale.

Effect of calcium availability and habitat quality on reproduction in Pied Flycatcher Ficedula hypoleuca and Great Tit Parus major

Recent studies have demonstrated that wild birds breeding in acidified areas may have difficulties in obtaining sufficient calcium for their eggshells, and that a shortage of land snails may be the cause. Here we present experimental evidence that calcium deficiency may affect reproductive traits also in birds breeding in non-acidified but naturally base-poor forest habitats. The study was conducted in Estonia in 1995 and 1996. We compared egg characteristics and other life-history traits of the Pied Flycatcher Ficedula hypoleuca and the Great Tit Parus major in two habitats differing in natural availability of calcium (base-poor pine forests and base-rich deciduous forests). In both species, egg volume was smaller in the poor than the rich habitat. Eggshell thickness also tended to be less in the poor habitat in 1996, but the difference was significant only in the Pied Flycatcher. An experimental supplementation of calcium was performed in the habitats to determine to what extent differences between rich and poor habitats might be caused by differences in calcium availability. Egg volume and shell thickness were positively affected by calcium supplementation in the Pied Flycatcher. The same tendency was observed in the Great Tit in 1996, although not significant. However, there was no effect of calcium provisioning on hatching success, nest desertion rate and number or quality of fledglings. Our results show that calcium limitation may occur in wild birds on naturally calcium-poor soils. Birds breeding in such habitats may be vulnerable to possible increases in acid deposition.

Hematological Health State Indices Predict Local Survival in a Small Passerine Bird, the Great Tit (Parus major)

In birds, it has been shown that reproductive effort may impair parental condition, while the relation of different condition indices to subsequent survival is still poorly understood. In this study, we measured body mass and various hematological condition indices in breeding great tits in relation to local survival. Number and quality of nestlings and the occurrence of second broods, potentially reflecting parents’ breeding effort, were also considered in analyses. The great tits, both male and female, that returned the following year had had a higher albumin/globulin ratio, lower plasma globulin concentration, and a lower heterophile/lymphocyte ratio during breeding in the preceding year, compared to those who did not return. Surviving males (but not females) also had had a higher level of circulating lymphocytes, compared to nonsurvivors. There was no correlation between breeding effort and survival. We conclude that better immunological state and lower stress in great tits during breeding were positively related to their survival probability.

Low Reproductive Success of Great Tits in the Preferred Habitat: A Role of Food Availability

Abstract: Habitat-related variation has been revealed in the seasonal reproductive patterns of great tits inhabiting mosaics of deciduous woodland fragments and managed coniferous forests. The number and quality of offspring tend to be higher in the non-preferred coniferous habitat compared with the preferred deciduous habitat. We explored whether these patterns can be explained by variation in food abundance and/or parental provisioning ability. Frass fall seemed not to be a reliable measure of the seasonal dynamics of nestling feeding conditions, although it is widely used for this purpose. No habitat-related differences were found in the tendency of parents to increase provisioning frequency in response to increased hunger levels of nestlings, suggesting that provisioning frequency as such is not a limiting factor for nestling growth. Higher feeding rates in deciduous habitat were associated with lower proportions of high-quality food items among prey delivered to offspring. These findings confirm that relatively high nestling feeding rates in birds may reflect the low quality of available food rather than the quality of parental care or an abundance of food in the environment. The results also indicate that deciduous forest habitat, though preferred by tits, may sometimes provide poorer brood-rearing conditions than the non-preferred, coniferous habitat. We suggest that the great tits preference for deciduous habitat, which presumably evolved in more southern regions, may be maladaptive in northern regions where deciduous woods are mainly young, secondary stands of alder and birch. Nomenclature: Tutin et al., 1993; Dickinson, 2003.

Evolutionary signals of selection on cognition from the great tit genome and methylome

For over 50 years, the great tit (Parus major) has been a model species for research in evolutionary, ecological and behavioural research; in particular, learning and cognition have been intensively studied. Here, to provide further insight into the molecular mechanisms behind these important traits, we de novo assemble a great tit reference genome and whole-genome re-sequence another 29 individuals from across Europe. We show an overrepresentation of genes related to neuronal functions, learning and cognition in regions under positive selection, as well as increased CpG methylation in these regions. In addition, great tit neuronal non-CpG methylation patterns are very similar to those observed in mammals, suggesting a universal role in neuronal epigenetic regulation which can affect learning-, memory- and experience-induced plasticity. The high-quality great tit genome assembly will play an instrumental role in furthering the integration of ecological, evolutionary, behavioural and genomic approaches in this model species.