Population dynamics of three songbird species in a nestbox population in Central Europe show effects of density,climate and competitive interactions

Unravelling the contributions of density‐dependent and density‐independent factors in determining species population dynamics is a challenge, especially if the two factors interact. One approach is to apply stochastic population models to long‐term data, yet few studies have included interactions between density‐dependent and density‐independent factors, or explored more than one type of stochastic population model. However, both are important because model choice critically affects inference on population dynamics and stability. Here, we used a multiple models approach and applied log‐linear and non‐linear stochastic population models to time series (spanning 29 years) on the population growth rates of Blue Tits Cyanistes caeruleus, Great Tits Parus major and Pied Flycatchers Ficedula hypoleuca breeding in two nestbox populations in southern Germany. We focused on the roles of climate conditions and intra‐ and interspecific competition in determining population growth rates. Density dependence was evident in all populations. For Blue Tits in one population and for Great Tits in both populations, addition of a density‐independent factor improved model fit. At one location, Blue Tit population growth rate increased following warmer winters, whereas Great Tit population growth rates decreased following warmer springs. Importantly, Great Tit population growth rate also decreased following years of high Blue Tit abundance, but not vice versa. This finding is consistent with asymmetric interspecific competition and implies that competition could carry over to influence population dynamics. At the other location, Great Tit population growth rate decreased following years of high Pied Flycatcher abundance but only when Great Tit population numbers were low, illustrating that the roles of density‐dependent and density‐independent factors are not necessarily mutually exclusive. The dynamics of this Great Tit population, in contrast to the other populations, were unstable and chaotic, raising the question of whether interactions between density‐dependent and density‐independent factors play a role in determining the (in) stability of the dynamics of species populations.     

Langfristige Bestandsentwicklung von Kohlmeise (Parus major) und Trauerschn?pper (Ficedula hypoleuca): Ergebnisse aus Niedersachsen

Zusammenfassung Im Mittel der Jahre 1957–1988 wurden bei Braunschweig (52.16 N/10.32 E) für die Kohlmeise 163 (Eichen-Hainbuchenwald), 90 (Laub-/Kiefernwald-Mischbestand) bzw. 55 (Kiefernforst) Brutpaare · 100 ha^–1 festgestellt. Beim Trauerschnäpper lagen die entsprechenden Zahlen bei 276, 250 bzw. 97. Die maximale Brutpaar-Dichte war bei der Kohlmeise um den Faktor 3,8 bis 4,3 und beim Trauerschnäpper um den Faktor 1,9 bis 2,6 höher als die jeweilige minimale Brutpaar-Dichte. Für den Trauerschnäpper ergab sich ein gesichert positiver Zusammenhang zwischen Erfolgsbruten-Zahl und Brutpaar-Dichte im jeweils folgenden Jahr. Bei der Kohlmeise war die Korrelation nicht signifikant. Der Bestandsverlauf der Kohlmeise zeigt eine gesicherte Zunahmetendenz, während sich für den Trauerschnäpper kein signifikanter Langzeit-Trend ergab. Beim Trauerschnäpper war die Brutpaar-Dichte von 1964–1975 gesichert höher als in den Zeiträumen 1957–1963 und 1976–1988 (Abb.).

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Longterm trends of Great Tits (Parus major) and Pied Flycatchers (Ficedula hypoleuca): Results in Lower Saxony

Summary From 1957 to 1988, the numbers of breeding pairs of Great Tits and Pied Flycatchers were ascertained in three nestbox equipped areas in the vicinity of Braunschweig/Lower Saxony (52.16 N/10.32 E; Tab. 1). In the Great Tits on average 163 breeding pairs per 100 hectares were registered in oak/hornbeam forest, 90 in mixed deciduous and pine forest, and 55 in pure pine forest. Corresponding figures for Pied Flycatchers were 276, 250, and 97. Maximum breeding pair density as compared to minimum density was greater by a factor of between 3.8 and 4.3 in the case of Great Tits, in the case of Pied Flycatchers it was greater by the factor of between 1.9 and 2.6. In the Pied Flycatchers a significantly positive correlation was established between the numbers of successful broods and breeding pair density in the year following. No significant correlation was found in the Great Tits. Density trends of Great Tits show a significant tendency of growth (summary of area data, see fig.) whilst no significant long term trend was recognisable for Pied Flycatchers. From 1964 to 1975 Pied Flycatcher breeding pair density was significantly greater than in the periods from 1957 to 1963 and from 1976 to 1988 (see fig.).

     

Nestbox orientation: a species-specific influence on occupation and breeding success in woodland passerines

Capsule Nestbox orientation has species-specific influences on nestbox occupation and breeding success for woodland passerines.

Aims To determine if nestbox orientation had an influence upon nestbox selection or breeding success for three co-occurring woodland passerines.

Methods We analysed 15 consecutive years of breeding data (1990–2004) from 295 nestboxes in the UK using circular statistical analyses to examine the influence of orientation upon nestbox occupation and breeding success for three species, Blue Tit Cyanistes caeruleus, Great Tit Parus major and Pied Flycatcher Ficedula hypoleuca.

Results The three species used nestboxes of all orientations during the 15-year period. The frequency of nestbox occupation by Great Tits correlated with orientation (the mean number of nests in boxes oriented south-southwest was lower than the mean number of nests in boxes facing other directions). There was no such relationship for Blue Tits or Pied Flycatchers. Nestbox orientation influenced the breeding success of Pied Flycatcher (the mean number of young to fledge from boxes oriented south-southwest was lower than from boxes facing other directions). There was no such relationship for Blue or Great Tits.

Conclusion Nestbox orientation can be an important influence on occupation and breeding success, but this differed between species. Intriguingly, although the directionality reduced nestbox occupation (Great Tit) and breeding success (Pied Flycatcher) was the same (south-southwest), there was a disparity in the influence of orientation for Great Tit (orientation influenced the frequency of occupation but not success) and Pied Flycatcher (orientation did not influence occupation but did affect success). We discuss these disparities, considering the possible influences of mating strategy, breeding phenology, nestbox microclimate and offspring quality.     

Parental provisioning behaviour in Pied Flycatchers Ficedula hypoleuca is well adjusted to local conditions in a mosaic of deciduous and coniferous habitat

Capsule Pied Flycatchers are better able than Great Tits to adjust their feeding behaviour to varying conditions in the same area.

Aims Great Tits breeding in a mosaic of deciduous and coniferous forests in the northern temperate region exhibit consistently lower breeding success in their preferred deciduous habitat than in coniferous habitat. This was explained by the unexpectedly poor nestling feeding conditions in deciduous forests of this region. We studied whether the same paradox applies to Pied Flycatchers that occupy the same habitats in the same area.

Methods Parental provisioning behaviour was studied using video‐recording and experimental manipulation. Caterpillar abundance and basic breeding parameters were measured in different habitat types.

Results Parental provisioning frequency and the proportion of caterpillars in nestling diet was lower, while food objects were on average larger, in coniferous compared with deciduous habitat. However, the total volume of caterpillars and adult Lepidoptera delivered to nestlings did not differ between habitats. In contrast to Great Tits, offspring body parameters in Pied Flycatchers did not differ between habitat types.

Conclusions These results demonstrate how the relative suitability of particular habitat types varies between species and is dependent upon geographical location.     

Pair bond and breeding success in Blue Tits Parus caeruleus and Great Tits Parus major

Data from 939 nests of the Blue Tit Parus caeruleus and 1008 nests of the Great Tit P. major from nestboxes provided in superabundance in mixed forest study sites between 1976 and 2001 were analysed to examine the effects of mate retention on breeding success and the relationship between mate fidelity and site fidelity. Most birds retained their former partner (76% in Great Tits and 65% in Blue Tits). The probability of a pair divorcing was affected by male age in Great Tits, divorce being more likely in pairs with first‐year males. Great Tit pairs breeding together for a second season bred earlier, but had no higher breeding success than pairs breeding together for the first time. In Blue Tits laying date and start of incubation tended to be earlier in pairs breeding together for a second season, but hatching and fledging dates were not earlier than in other pairs. Great Tit pairs breeding together for two consecutive seasons bred earlier in the second season than in the first, but breeding success did not differ significantly between years. In both species, breeding performance did not differ between pairs that divorced after a season and pairs that stayed together. Thus breeding success did not determine whether a pair divorced or bred together again. Neither Blue Tits nor Great Tits improved their breeding performance through divorce. Blue Tit females even had fewer fledglings in the year after divorce than in the year before. Mate retention affected breeding site fidelity. Blue Tit females had greater breeding dispersal distances between consecutive years when re‐mating than when breeding again with the same mate. In Great Tits both males and females dispersed more when re‐mating than when retaining the former partner, suggesting that mate retention increased the chance of retaining the breeding site. In both species, breeding dispersal distances did not differ between pairs that divorced and pairs in which one mate disappeared. Because no major advantage of mate retention was evident, we suggest that mate retention evolved under different conditions than those found in study sites with high breeding densities and a superabundance of artificial nesting sites.     

Female ornaments in the Pied Flycatcher Ficedula hypoleuca: associations with age, health and reproductive success

Female ornamentation has received little attention in studies of sexual selection. Traditionally, female ornaments have been explained as a genetically correlated response to selection in males. However, recent findings suggest that female ornaments may be adaptive. Southern populations of Pied Flycatchers Ficedula hypoleuca are suited for studies of female ornamentation because, in addition to the white wing patch, some females also express the white forehead patch characteristic of males. We thus addressed the associations of these two ornaments with female age and with some health and breeding parameters in a Spanish population of Pied Flycatchers. Female ornament expression was not associated with haemoparasite prevalences, clutch size or parental provisioning effort. However, females expressing the white forehead patch raised more fledglings, and females with larger wing patches bred earlier, had higher number of hatchlings and showed increased levels of total serum immunoglobulins. Thus, these two unrelated epigamic ornaments may indicate some aspects of female quality. Further experimental studies could test the possibility that these plumage traits might function as signals to the males or might be used during female–female aggressive encounters in competition for nest-sites and mates.     

Variation in effects of male plumage ornaments: the case of Iberian Pied Flycatchers

It has been proposed that mate preferences by female Pied Flycatchers Ficedula hypoleuca differ between southern (Iberian) and northern (Scandinavian) European populations. Whereas the size of the white forehead patch, but not plumage colour, has been reported to be a sexually selected trait in the former, only plumage darkness apparently acts as an ornament in the latter. In addition, northern male Pied Flycatchers become darker with age, a trend not detected until the present study in southern birds. Here we show that in an Iberian population of Pied Flycatchers breeding only a few tens of kilometres from previously studied populations, plumage darkness is associated with mating success and increases with age, whereas the size of the white forehead patch is not related to mating success and is only weakly correlated with age, trends similar to those reported for Scandinavian rather than other Iberian Pied Flycatcher populations. This represents a case of variation in sexually selected traits between geographically close populations of Pied Flycatchers that cannot be explained by sympatry with closely related species. It is proposed that differences in the identity and abundance of environmental stressors may be the cause of this regional variation in sexually selected traits.     

Do extended incubation recesses carry fitness costs in two cavity‐nesting birds?

Because extended incubation recesses, where incubating songbirds are away from nests for periods much longer than usual, occur infrequently, they have been treated as outliers in most previous studies and thus overlooked. However, egg temperatures can potentially fall below the physiological zero temperature during extended recesses, potentially affecting developing embryos. As such, evaluating extended recesses in an ecological context and identifying their possible fitness effects are important. With this aim, we used iButton data loggers to monitor the incubation behavior of female Blue Tits (Cyanistes caeruleus) and Great Tits (Parus major) during two breeding seasons in central Spain. We classified incubation recesses as extended if they were more than four times the mean recess duration for each species. Extended incubation recesses occurred more frequently in 2012 when females exhibited poorer body condition. Female Blue Tits had more extended incubation recesses than female Great Tits and, for both species, more extended recesses occurred at the beginning of the breeding season. Both nest attentiveness and average minimum nest temperature decreased when at least one extended recess occurred. Incubation periods averaged 4 d longer for nests where females had at least one extended recess, potentially increasing predation risk and resulting in lower‐quality nestlings. Overall, our results suggest that extended recesses may be more common among songbirds than previously thought and that, due to their effects on egg temperatures and attentiveness, they could impose fitness costs.     

Climate change affects breeding of reed warblers Acrocephalus scirpaceus

Between 1970 and 2006 reed warblers Acrocephalus scirpaceus started breeding progressively earlier; both the initiation of breeding (the earliest first egg dates) and peak of breeding (median first egg dates) advanced. Median first egg dates correlated significantly with increasing May–July mean temperatures. However, in contrast to other studies showing the advancement in laying dates, the end of the season did not shift. As a result, the breeding season is now longer increasing re-nesting opportunities. Individuals are able to re-nest 4–5 times, which might have important implications for the species. It was also found that in warmer seasons the population suffered fewer nest losses. Both factors, higher re-nesting potential and a trend toward fewer losses, should lead to increased fitness of individuals in the studied population.     

Mobbing behaviour: reciprocity-based co-operation in breeding Pied Flycatchers Ficedula hypoleuca

Recent non-experimental evidence suggests that reciprocal altruism may be more common in nature than was previously thought. Here we present experimental evidence for mobbing behaviour as reciprocal altruism in breeding Pied Flycatchers Ficedula hypoleuca , a small migratory passerine. Pied Flycatchers attended mobs initiated by their co-operating neighbours. However, they did not join in mobbing initiated by their conspecific neighbours when not assisted in the test an hour before. The results suggest that birds followed a 'tit-for-tat-like' strategy and that responses of neighbouring Flycatchers may be related to reciprocal altruism.     

Male colour variation in Spanish Pied Flycatchers Ficedula hypoleuca

Male variation in dorsal plumage colour was studied in a montane Spanish population of Pied Flycatchers Ficedula hypoleuca. Adult and yearling males did not differ in colour as measured by Drost's colour types. However, adult males differed from yearlings in being more likely to die if they were light-coloured the year before. Following the same individual males across years yielded a trend towards adult males becoming browner the following year, while no significant differences were found in first-year males. For surviving individual males, becoming browner between successive breeding seasons was associated with relative delays in breeding phenology. Significant but not very high repeatability of male colour is found, and this trait may be subjected to moderate environmental variation, perhaps while moulting in the winter quarters. Overall, being browner may be a sign of ageing and/or poor condition in Spanish Pied Flycatchers.     

Bacterial degradability of white patches on primary feathers is associated with breeding date and parental effort in a migratory bird

We compared the in vitro bacterial degradability of the white patch and melanized area of primary feathers of breeding male and female Pied Flycatchers Ficedula hypo‐leuca and related this variation to laying date, brood size and brood mass. Bacterial degradability of male and female white feather patches, but not of melanized areas, was positively correlated with laying date. Male Pied Flycatchers showed a positive correlation between bacterial degradability of the white patch, though not of the melanized patch, and brood size and brood mass. Feather degradability appears to be negatively related to individual quality and positively related to reproductive effort.     

The effect of nestboxes on breeding populations of birds in broadleaved temperate woodlands

Removal of nestboxes from a semi-mature, broadleaved woodland caused a decrease in the number of breeding pairs of Great Tits, but did not significantly reduce breeding densities of Blue Tits. Breeding densities of warblers were unaffected by changes in the population of Great Tits. In the absence of nestboxes, intraspecific competition for natural nestholes was more intense amongst Great Tits than Blue Tits. Great Tits tended to occupy larger holes on or near the trunk, while Blue Tits used smaller holes on side branches. Nesting success for both species was lower in natural cavities than nestboxes, due to a higher percentage of total nest failures. The reintroduction of nestboxes did not produce an immediate rise in the breeding population of Great Tits; possible reasons for this are discussed.     

The effect of nestboxes on breeding populations of birds in broadleaved temperate woodlands

Removal of nestboxes from a semi-mature, broadleaved woodland caused a decrease in the number of breeding pairs of Great Tits, but did not significantly reduce breeding densities of Blue Tits. Breeding densities of warblers were unaffected by changes in the population of Great Tits. In the absence of nestboxes, intraspecific competition for natural nestholes was more intense amongst Great Tits than Blue Tits. Great Tits tended to occupy larger holes on or near the trunk, while Blue Tits used smaller holes on side branches. Nesting success for both species was lower in natural cavities than nestboxes, due to a higher percentage of total nest failures. The reintroduction of nestboxes did not produce an immediate rise in the breeding population of Great Tits; possible reasons for this are discussed.     

Population limitation in Palaearctic-African migrant passerines

We report the results of key factor analyses for Sedge Warbler Acrocephalus schoenobaenus, Blackcap Sylvia atricapilla, Whitethroat Sylvia communis and Willow Warbler Pftylloscopus Irochilus based on extensive data from the United Kingdom gathered by the British Trust for Ornithology. These results are compared with those from published key factor analyses based on intensive studies of Swallows Hirundo ruslica, Redstarts Phoenicurus phoenicums and three populations of Pied Flycatchers Fiiedula hypoleuca. Variation in losses between fledging and the following breeding season lk₄ ) accounted for most of the variation in total losses (K_T) for all populations. Breeding performance was poorly correlated with population changes. Density-dependence was found mainly in 6₄, its strength decreasing as average rate of population change increased. There was also evidence of weak density-dependence in the clutch size of Swallows and in Willow Warbler egg losses. Fluctuations in k₄ were correlated with conditions on the wintering grounds in Sedge Warblers, Whitethroats and Swallows, for the first two species these relationships being confirmed by analyses of independent survival estimates based on mark-recapture data. Populations of Sedge Warblers and Whitethroats appear to be limited by competition for resources on the wintering grounds. Removal experiments suggest that Willow Warblers, Pied Flycatchers and perhaps Blackcaps are limited through recruitment to the breeding population, in the case of Pied Flycatchers this limitation being in relation to the availability of nest sites.     

Parid foraging choices in urban habitat and their consequences for fitness

Urban environments are habitat mosaics, often with an abundance of exotic flora, and represent complex problems for foraging arboreal birds. In this study, we used compositional analysis to assess how Blue Tits Cyanistes caeruleus and Great Tits Parus major use heterogeneous urban habitat, with the aim of establishing whether breeding birds were selective in the habitat they used when foraging and how they responded to non‐native trees and shrubs. We also assessed whether they showed foraging preferences for certain plant taxa, such as oak Quercus, that are important to their breeding performance in native woodland. Additionally, we used mixed models to assess the impact of these different habitat types on breeding success (expressed as mean nestling mass). Blue Tits foraged significantly more in native than non‐native deciduous trees during incubation and when feeding fledglings, and significantly more in deciduous than evergreen plants throughout the breeding season. Great Tits used deciduous trees more than expected by chance when feeding nestlings, and a positive relationship was found between the availability of deciduous trees and mean nestling mass. Overall, the breeding performance of both species was poor and highly variable. Positive relationships were found between mean nestling mass and the abundance of Quercus for Great Tits, but not for Blue Tits. Our study shows the importance of native vegetation in the complex habitat matrix found in urban environments. The capacity of some, but not all, species to locate and benefit from isolated patches of native trees suggests that species vary in their response to urbanization and this has implications for urban ecosystem function.     

A meta-analytic study of the effects of female age on laying-date and clutch-size in the Great Tit Parus major and the Pied Flycatcher Ficedula hypoleuca

The effects of age (1 year-old vs older females) on laying-date and clutch-size of the Great Tit Parus major (in eight independent study areas) and the Pied Flycatcher Ficedula hypoleuca (five areas) were meta-analysed using both published and unpublished records. To standardize comparisons between areas and species, the standardized difference between the means of the two age groups was used as a measure of the magnitude of the age-effect (effect size).
In Great Tits the laying-date of 'young' females was 0.30 standard deviation units later and clutch-size 0.31 units smaller than that of 'old' females. In the Pied Flycatcher the corresponding figures were 0.45 and 0.81, respectively. All the effect size measures were highly significant but for clutch-size the effect size of the Pied Flycatcher was significantly greater than that of the Great Tit. In the Great Tit the effect size of clutch-size was heterogeneous across the different study areas.
It was estimated that the following numbers of unpublished studies showing null results would have to have accumulated in file-drawers before we could say that the results concerning effect sizes are due to sampling bias: for Great Tits 121 studies of laying-date and 196 studies of clutch-size; and for Pied Flycatchers 45 studies of laying-date and 139 studies of clutch-size.     

When to start and when to stop: Effects of climate on breeding in a multi‐brooded songbird

Climate warming has been shown to affect the timing of the onset of breeding of many bird species across the world. However, for multi‐brooded species, climate may also affect the timing of the end of the breeding season, and hence also its duration, and these effects may have consequences for fitness. We used 28 years of field data to investigate the links between climate, timing of breeding, and breeding success in a cooperatively breeding passerine, the superb fairy‐wren (Malurus cyaneus). This multi‐brooded species from southeastern Australia has a long breeding season and high variation in phenology between individuals. By applying a “sliding window” approach, we found that higher minimum temperatures in early spring resulted in an earlier start and a longer duration of breeding, whereas less rainfall and more heatwaves (days > 29°C) in late summer resulted in an earlier end and a shorter duration of breeding. Using a hurdle model analysis, we found that earlier start dates did not predict whether or not females produced any young in a season. However, for successful females who produced at least one young, earlier start dates were associated with higher numbers of young produced in a season. Earlier end dates were associated with a higher probability of producing at least one young, presumably because unsuccessful females kept trying when others had ceased. Despite larger scale trends in climate, climate variables in the windows relevant to this species’ phenology did not change across years, and there were no temporal trends in phenology during our study period. Our results illustrate a scenario in which higher temperatures advanced both start and end dates of individuals’ breeding seasons, but did not generate an overall temporal shift in breeding times. They also suggest that the complexity of selection pressures on breeding phenology in multi‐brooded species may have been underestimated.     

Climate change, migratory connctivity and changes in laying date and clutch size of the pied flycatcher

We examined long-term (1943–2003) variability in laying dates and clutch sizes in a Finnish population of the pied flycatcher Ficedula hypoleuca Pallas, and analysed whether potential changes were explained by changes in climatic factors at the wintering area in Africa, at migration route or at breeding grounds. Among-year variation in both mean and skewness of laying dates increased, which for mean laying date appeared to be explained by variability of temperatures at the breeding grounds and for skewness by variable temperature trends along the migration route. Pied flycatchers bred earlier in warm springs, but despite a warming trend in pre-laying temperatures, the laying dates tended to delay. Laying dates became continuously later in relation to the phenology of the environment. Mean clutch size decreased with time when mean laying date was controlled for, but the climatic factors did not appear to explain the decrease. The advancement of spring phenology may have shifted some food sources needed for egg-laying, thus leading to later laying and smaller clutches. Variation in clutch size increased when wintering conditions were favourable so that clutch size distribution was skewed with a tail of small clutches when there had been lot of rainfall (more vegetation and insects) in the wintering area. We suggest that when ecological conditions during winter were good, the tail of small clutches represented low-quality individuals that were not able to breed after bad winters. Our analyses demonstrate that measures of spread and symmetry give different information about population level changes than means, and thus complement the understanding of the potential influences of climate change on populations.     

Seasonal decline in provisioning effort and nestling mass of Blue Tits Cyanistes caeruleus: experimental support for the parent quality hypothesis

A common feature of many birds breeding in seasonal environments is that fitness‐related parameters such as nestling mass or survival decline as the breeding season progresses. Consequently, there is a tendency for early breeders to have better reproductive performance than individuals breeding later in the season. This variation could be caused by factors associated with the date of laying, such as changing environmental conditions (date hypothesis), or by differences in parental quality between early and late breeders (parent quality hypothesis). To evaluate the relative importance of both hypotheses, we manipulated hatch dates of Blue Tits Cyanistes caeruleus by exchanging clutches with different incubation stages and assessed the impact on nestling mass, nestling diet and provisioning rates. Mean nestling mass declined significantly over the season. This was the combined result of differences in parental quality, which dominated in the early part of the season, and the influence of hatching date (date effect per se), which prevailed later in the season. Nestling diet composition was apparently uninfluenced by the manipulation, suggesting that deteriorating food supplies are the primary reason for the seasonal variation in the nestling diet. Counter to the date hypothesis, delayed parents did not feed their young less than control pairs did, but in fact exhibited higher provisioning rates. Our results suggest that in this population, parental quality seems to constrain post‐hatching reproductive performance and such intrinsic limitations may help to explain why certain individuals breed later.