Markku Orell

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.

Role of heredity in egg size variation in the Great Tit Parus major and the Pied Flycatcher Ficedula hypoleuca

Phenotypic correlations between body size and egg dimensions were poor in the Great Tit and Pied Flycatcher populations studied in northern Finland. Heritability of egg volume was high in the Great Tit, 0.86+0.29. The phenotypic effect of a female upon egg dimensions was great, about 60% of total variance, and this was interpreted as the approximate effect of additive genetic factors. The age of the female had slight effects on egg dimensions, and clutches of different years and the first and second clutches of the same year had similar egg dimensions, although clutch size decreased significantly during the season in the Great Tit. However, egg size as well as the effect of non-heritable factors on egg size increased in replacement clutches laid shortly after the first clutch. The high heritability of egg dimensions implies that egg size should rapidly respond to differential selection pressures, but geographical variation in egg size has not been found in the species studied. However, selection pressures affecting the adaptive variation of egg size in an English Great Tit population were concluded to differ from those operating in northern Finland.

Prior residency as a key determinant of social dominance in the willow tit (Parus montanus)

SummaryWe studied how age, body size and prior residency affected social dominance in the willow tit (Parus montanus) groups. The contribution of each variable was experimentally tested in unisexual two-bird trials, in which the birds were matched for all variables except the one studied. Large birds were dominant over smaller ones (Fig. 1). The effect of body size was more prominent in males than in females. Age had no influence on dominance. Residents became dominant more often than newcomers (Fig. 2). Adulthood or larger body size did not override the advantage of prior residency (Fig. 2). Therefore, the proximate reason for the age-dependent dominance seen in natural willow tit flocks is most likely the prior residency advantage of the adults. Factors connected with fighting ability (body size and age) seem to be less important than the time of establishment of rank, which may reflect the importance of resource value differences between residents and newcomers in this context. The advantage of residency might make it advantageous to be a member of a flock even as a subordinate, rather than being solitary.

Evolution and genetic structure of the great tit (Parus major) complex

The great tit complex is divided into four groups, each containing several subspecies. Even though the groups are known to differ markedly on morphological, vocal and behavioural characters, some hybridization occurs in the regions where they meet. The great tit has often been referred to as an example of a ring species, although this has later been questioned. Here, we have studied the genetic structure and phylogenetic relationships of the subspecies groups to clarify the evolutionary history of the complex using control region sequences of the mitochondrial DNA. The subspecies groups were found to be monophyletic and clearly distinct in mitochondrial haplotypes, and therefore must have had long-independent evolutionary histories. This conflicts with the ring species assignment and supports the formation of secondary contact zones of previously temporarily isolated groups. According to the phylogenetic species concept, all the subspecies groups could be considered as separate species, but if the definition of the biological species concept is followed, none of the subspecies groups is a true species because hybridization still occurs.

Do subordinates expose themselves to predation? Field experiments on feeding site selection by Willow Tits

To examine the relationship between social dominance and exposure to predation risk, we allowed natural groups of Willow Tits Parus montanus to choose between two nearby feeding sites differing in safety. The birds preferred to feed at the safe site. Socially dominant individuals used safe sites more than did subordinates. However, adult females mated with alpha males, used safe sites more than expected from their rank, possibly as a result of protection offered by their mates. Subordinates increased their use of safe sites after experimental removal of dominants, implying that the greater risk-taking of subordinates in natural flocks is due to interference from dominants. The observed pattern of risk-taking at feeders may influence survival also in natural conditions, because dominants survive better than subordinates, as documented earlier for this population.

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.

TIME AND FOOD DEPENDENCE IN WILLOW TIT WINTER SURVIVAL

Timing of mortality was studied in Willow Tits (Parus montanus) during three winters, 1991–1993 and 1995–1996, near Oulu, northern Finland. The aim of this study was, by investigating monthly winter survival rates, to examine (1) whether late winter is the most difficult time for birds, and (2) whether temperature, especially in late winter, correlates with survival, as previously proposed. We also sought information on sex and age differences in timing of mortality, rarely studied among passerines. After color-marking, individuals were resighted monthly from September to May. Capture–recapture models were applied to separately estimate survival and resighting probabilities. Survival estimates given by three methods of varying complexity (simple counts, Jolly-Seber, Cormack-Jolly-Seber) were compared. The three different methods yielded similar survival estimates. Because simple counting does not account for emigration, consistent results from different analyses support the earlier view that Willow Tits are sedentary. Adults survived better than yearlings in all winters and exhibited more constant survival rates. Two-year data also suggest that winter and summer survival rates were similar in adults, but not in yearlings, for which mortality was greatest in winter. Males survived better than females in one winter. Temperature per se did not correlate with survival, but deviations to colder than long-term average temperature seemed to be associated with low survival probability, which could reflect occasional food limitation. A feeding experiment was conducted to test the winter food limitation hypothesis. Fed birds survived winter better than did control birds, significantly so in yearlings and males, but not in adults or females. Previously, late winter has been suggested as being a difficult time for birds. However, no support was found for this hypothesis. Small passerines wintering at high latitudes seem to be able to cope with high energy demand and the limited foraging time of winter.

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.

Cost of reproduction: parental survival and production of recruits in the Willow Tit Parus montanus

SummaryBrood sizes of the Willow Tit were altered experimentally by subtracting or adding two nestlings in 1986 and 1987 in the vicinity of Oulu, northern Finland. The manipulated broods were within the normal range observed in natural conditions. Unaltered broods were used as controls. Data from natural broods from 1978–1985 were available for comparison. When the nestlings were 13 days old they were ringed and weighed and their tarsus, wing, and tail lengths were measured. On the same day the parents were caught, weighed, and measured. In 1986 there were no differences in nestling mortality between the reduced, control, or enlarged broods; i.e. parents were able to fledge the two extra young. In 1987 starvation was most pronounced in the enlarged broods. This resulted in the number of fledglings being practically the same in each manipulation category. Especially the body weight, but also the other indices of body size, decreased as a function of the brood size category, suggesting that there may be quality differences between the young reared in different experimental groups. In 1986 there was a non-significant trend towards lower body weight of the parents attending reduced, control, or enlarged broods, in that order. In 1987 the differences were much smaller. These results were not due to size differences between the groups, so possibly the increased reproductive effort of raising extra young was responsible for the trend observed in 1986. There were no significant differences in parental survival associated with the manipulation category, although the trend in the females was consistent with the hypothesis of reproductive cost. It is possible that environmental conditions in 1986 were so favourable that the tits were not unduly stressed even when attending two extra young. Correlative data from 1978–1985 did not support the cost hypothesis either. A non-significant trend towards reduced post-fledging survival and recruitment of the young was observed with increased brood size. The average fitness value of parents, incorporating parental survival and number of recruits, showed that the success of the adults raising enlarged broods may be lower than that of others. It seems that the reproductive cost, if it exists, decreases individual fitness value by reducing the chances of recruiting descendants into the next generation. The reproductive stress may be insufficient to reduce the subsequent survival of parents. More data are however needed to confirm these results.

Phylogeography of a Palaearctic sedentary passerine, the willow tit (Parus montanus)

We analysed variation of the mitochondrial control region from willow tits through its Palaearctic distribution range. Although we found high amount of genetic variation (π=1.114%), there was almost no differentiation between subspecies or geographical localities. This may be because of a combination of several ecological and genetic factors, including a relatively homogenic habitat through the distribution range, lack of geographical barriers, high gene flow and a large long‐term effective population size. On the contrary, in the songar tit, which is sometimes considered to be conspecific with the willow tit, the mitochondrial lineages seem to correlate with the geographical locality and are clearly distinct from the willow tit. We concluded that the common ancestors of willow and songar tits existed some 1.5–2 Myr ago in the south‐eastern Asia. After the last Ice Ages, the willow tit expanded all through the Palaearctic, whereas the songar tit remained in eastern Asia.