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Climate change affects timing of reproduction in many bird species, but few studies have investigated its influence on annual reproductive output. Here, we assess changes in the annual production of young by female breeders in 201 populations of 104 bird species (N = 745,962 clutches) covering all continents between 1970 and 2019. Overall, average offspring production has declined in recent decades, but considerable differences were found among species and populations. A total of 56.7% of populations showed a declining trend in offspring production (significant in 17.4%), whereas 43.3% exhibited an increase (significant in 10.4%). The results show that climatic changes affect offspring production through compounded effects on ecological and life history traits of species. Migratory and larger-bodied species experienced reduced offspring production with increasing temperatures during the chick-rearing period, whereas smaller-bodied, sedentary species tended to produce more offspring. Likewise, multi-brooded species showed increased breeding success with increasing temperatures, whereas rising temperatures were unrelated to reproductive success in single-brooded species. Our study suggests that rapid declines in size of bird populations reported by many studies from different parts of the world are driven only to a small degree by changes in the production of young., This meta-analysis was financed by the grant of the Polish National Science Centre (Narodowe Centrum Nauki) (no. 2017/27/B/NZ8/00465) awarded to Lucyna Hałupka.

Long-term and short-term changes in ambient temperature can cause stress in birds, leading to changes in the level of hematological parameters. The H:L ratio (heterophil-to-lymphocyte ratio) is a hematological index that allows for the assessment of the stress induced by environmental changes, including weather conditions. In this paper, we examined the influence of temperatures and the sum of precipitation on the health of nestling pied flycatchers (Ficedula hypoleuca) by using the H:L ratio reflecting the body’s response to stress. All examined temperature indicators influenced the H:L ratio, yet the average value of daily minimum temperature during the first 12 days of nestling life had the strongest influence, maximum temperature had the weakest effect, while precipitation had no significant influence. Our research indicates that even a small increase in temperature caused a stress reaction in nestling pied flycatchers, which was reflected by an increase in the H:L ratio. The increase in the stress index (H:L ratio) was probably a result of poor weather conditions (precipitation, low temperature), which prevented the adult birds from actively foraging and properly feeding the nestlings.

Among environmental factors affecting life - history traits of birds breeding in nest boxes, an influence of microbial communities is relatively poorly understood. In this study, nest boxes used for breeding by great tit (Parus major) and blue tit (Cyanistes caeruleus) were sampled before the start of the breeding season to assess the bacterial loads of the nest box. Samples from the entrance hole and the interior of the nest box were taken at two different study sites: an urban parkland and a natural forest. Nest boxes were sampled to check if their bacterial loads differed between habitats. The second objective of this study was to check whether the occupancy of the nest boxes during the previous season would influence the bacterial load of the nest box. To verify this prediction, two categories of nest boxes were sampled at both study sites: nest boxes occupied by any of the two tit species in the previous season for breeding and nest boxes that had remained empty that year. The bacterial load of the nest box was significantly higher in the forest study area in both the occupied and unoccupied nest boxes. The nest boxes used for breeding in the previous season had significantly higher bacterial loads, but only in the forest area. Our results suggest that the bacterial load of the nest box can vary between habitats and may be positively related to the presence of the nests in the previous breeding season.

Landscape conversions induced by human activities can affect dispersal patterns of various bird species and, as a result, affect genetic structure of their populations. Genetic differentiation of bird populations may be enhanced by habitat variation, especially in urban-non-urban systems. The majority of population genetic studies focus on single species, which inflicts limitations for direct comparisons of genetic responses of avian populations to urbanization. Here, we used a set of microsatellite markers to examine genetic diversity, gene flow and population structure in two common parid species, great tits Parus major and blue tits Cyanistes caeruleus occupying three sites in habitats with contrasting urbanization level in central Poland. We found low but significant divergence of urban park population with both suburban and non-urban forest great tit populations, while no differentiation was found between suburban forest and non-urban forest populations. In contrast, no evidence for genetic differentiation was found between blue tit populations from the urban park, suburban forest and non-urban forest sites. We conclude that great tits and blue tits respond to urbanization-related changes in a different way, which may be a result of different rates of migration and/or dispersal, likely higher in blue tits. Some impact may be also induced by interspecific competition. We suggest that changing the focus of urban genetic research from single to multiple species may provide novel insights into how natural populations respond to the processes of urbanization.

A considerable number of avian species tend to use bryophytes as nest construction material, but the selectivity of birds in their bryophyte use in nest construction in relation to the availability of particular mosses in individual territories remains largely unexplored. We studied the bryophyte composition of nests in two passerine species: the Blue Tit Cyanistes caeruleus and the Great Tit Parus major in two floristically and structurally contrasting study areas (a mature deciduous forest and an urban parkland). We also studied territories within a radius of 10 m from each occupied nest box, listing all bryophyte species and checking to what extent the moss composition of the nest reflected what was available in the surrounding of the nest box. Both tit species appeared to be selective. The tits used a total of 31 bryophyte species in their nests (27 found in Blue Tits and 19 in Great Tits), whereas 25 additional bryophyte species were found around (10 m radius) the studied nests, but not in the nests. The number of bryophyte species found in individual nests varied in the urban parkland between 1 and 6 and in the forest between 1 and 11. The average number of bryophytes in the nest ranged from 2.31 in Great Tit from the urban parkland to 3.52 in Blue Tit in the urban parkland. Only a few species were used in a higher proportion than 5% of the volume within a single nest and, considering only these most abundant bryophyte species, the mean number ranged from 1.28 in Great Tits in the forest to 1.57 in Blue Tits in the urban parkland. Our study also showed that, in general, the bryophyte species composition of the nests seems to be affected by the site (the urban park vs the forest) rather than the parid species (Blue Tit vs Great Tit).

Nests of secondary-cavity breeding birds are structures constructed to lay and incubate eggs and raise nestlings to fledging. These nests are characterized by relatively stable conditions, which makes them a suitable habitat for various microorganisms. It has been suggested that bacteria inhabiting nests and nestling skin may affect nestlings both positively and negatively. In this study, nests of Great Tits Parus major were replaced with artificial nests on the fifth day of the nestling phase in two different study sites to create two categories of nests: (i) natural and (ii) artificial with a reduced bacterial load. Four days later, bacterial samples were collected from the nestling skin and from the edge of the nest to assess skin and nest bacterial loads, expressed as colony forming units (CFUs). It was predicted that (i) the previous season occupancy of nest boxes would influence bacterial loads, (ii) the experimental treatment would reduce nest and skin bacterial loads, and (iii) that nest and skin bacterial loads would affect the condition of the nestlings, assessed as the hemoglobin concentration in blood when nestlings were 14 days old. Occupancy in the previous season did not affect the bacterial load. The skin bacterial load was significantly lower in artificial nests, although the nest bacterial load did not differ between natural and artificial nests. Nestlings from artificial nests had higher hemoglobin, and hemoglobin concentration was negatively associated with the nest but not the skin bacterial load. Our results suggest that the bacterial load in nests may negatively affect the physiological condition of avian hosts.

Ketone body levels, among other biochemical blood indices, are important indicators of the physiological condition of birds. Plasma ketone as an indicator of fasting and lipid use is strongly linked to demanding phases in the avian life cycle, such as migration or wintering. The main goal of this study was to check whether ketone body levels differ between the habitats in which individuals stay in winter. To test the above prediction, we used a portable point-of-care device to measure ketone body levels in wintering great tits (Parus major). We assumed that wintering in distinct habitats that differ structurally, particularly with respect to food availability, would affect the metabolic performance of birds and their physiological condition. Individual great tits were trapped in mist nets and blood-sampled in three distinct locations within the city: an urban parkland, the deciduous forest and a city centre. As expected, we showed that the mean ketone level was significantly higher in the area where artificial feeding was irregular than in two areas of regular feeding, indicating the more intense fasting state there. We also checked if the level of ketone bodies differs with respect to the sex of an individual, but we found no such difference.

Among environmental factors affecting life - history traits of birds breeding in nest boxes, an influence of microbial communities is relatively poorly understood. In this study, nest boxes used for breeding by great tit (Parus major) and blue tit (Cyanistes caeruleus) were sampled before the start of the breeding season to assess the bacterial loads of the nest box. Samples from the entrance hole and the interior of the nest box were taken at two different study sites: an urban parkland and a natural forest. Nest boxes were sampled to check if their bacterial loads differed between habitats. The second objective of this study was to check whether the occupancy of the nest boxes during the previous season would influence the bacterial load of the nest box. To verify this prediction, two categories of nest boxes were sampled at both study sites: nest boxes occupied by any of the two tit species in the previous season for breeding and nest boxes that had remained empty that year. The bacterial load of the nest box was significantly higher in the forest study area in both the occupied and unoccupied nest boxes. The nest boxes used for breeding in the previous season had significantly higher bacterial loads, but only in the forest area. Our results suggest that the bacterial load of the nest box can vary between habitats and may be positively related to the presence of the nests in the previous breeding season.

Ketone body levels, among other biochemical blood indices, are important indicators of the physiological condition of birds. Plasma ketone as an indicator of fasting and lipid use is strongly linked to demanding phases in the avian life cycle, such as migration or wintering. The main goal of this study was to check whether ketone body levels differ between the habitats in which individuals stay in winter. To test the above prediction, we used a portable point-of-care device to measure ketone body levels in wintering great tits (

It has been suggested that extreme weather events may be treated as natural experiments that may unravel the mechanisms by which birds adjust their phenology and breeding parameters to environmental variability. In 2017, a sudden and heavy drop of temperatures for several days affected many European bird populations. This event occurred during the laying–early incubation period in the great tit (Parus major) population in central Poland, causing a large delay in hatching and had sustained reproductive consequences. This cold snap occurring once breeding activity had already started in 2017 was followed by the warm and invariable breeding season of 2018. This natural experiment had an essential influence on great tit reproductive parameters. We found a significant difference in hatching date, number of fledglings, hatching success, and fledging success between 2017 and 2018. In 2017, there were about two fledglings per nest fewer than in 2018. Fledging success was positively associated with hatching delay in 2017, while the relation was negative in 2018. Hatching success differed significantly between both years, being higher in 2018. Mean level of hemoglobin (used as index of body, physiological condition) in the blood of nestling great tits was higher in 2017 than in 2018. We argue that the moment of hatching may be (at least in some years) more tightly related to the moment of maximum food demand of tit nestlings than the traditionally used laying date. Also in extreme years, phenotypic plasticity of hatching delays may be insufficient to adjust the timing of breeding to the upcoming extreme weather events. Further examining its limits may be an important goal for future research.

The great tit Parus major inhabits various types of forests, yet it prefers deciduous forests. In the urbanized areas it is one of the commonest bird species, even where only isolated trees are present, which seems to be a relatively recent phenomenon. This paper presents results of a long-term study (2002–2015) of variation in reproductive performance (number of hatchlings, hatching success, number of fledglings, fledging success, breeding success and nest failure rate) in first clutches of two great tit populations nesting in two contrasting habitats: a mature deciduous forest and an urban parkland, in central Poland. This study shows a clear and sustained spatial pattern of variation where the forest population of great tits produced more hatchlings and fledglings per successful nests than the urban park site population. Breeding success and fledging success demonstrate a similar but slightly less obvious pattern, with higher values for the forest site than the urban parkland area occurring consistently in the vast majority of years. Also hatching success was generally slightly higher in the forest than in the urban park but did not show such a clear spatial pattern. Only the nest failure rate was higher in the forest than in the urban parkland. We suggest that caterpillar richness in the forest compared to the urban parkland is one of the key drivers of the observed differences in the breeding performance between the study habitats. We also found positive correlations between fledgling numbers and caterpillar abundance and between fledgling numbers and mean May temperatures in the forest, whereas neither breeding nor fledging success showed such correlations. In the urban parkland, fledgling numbers as well as fledging and breeding successes were positively correlated with mean May temperatures. The between-population variation we found probably reflects a more general difference between urban and forest populations of tits.

The causes and consequences of variation in the incubation regimes of oviparous animals remain unclear, despite having important fitness consequences. Avian incubation regimes can be shortened by parents initiating incubation prior to clutch completion or prolonged when there are gaps in the laying sequence. Here, we begin by quantifying variation in the incubation regimes of three populations of blue tits Cyanistes caeruleus from the UK and Poland before examining the consequences of such variation for their hatching and fledging success. We then investigate the mechanism causing such variation by exploring the impact of local weather conditions on incubation regimes. The difference between the expected and actual hatching dates of clutches was termed the “hatching deviation” and this showed considerable variation. Hatching deviation was negatively related to local temperature and clutch size. Hatching deviation affected hatching success and hatching deviation, temperature, wind speed and clutch size affected fledging success. Deviating from the expected laying and incubation regime caused lowered reproductive success. The most successful birds were those that were able to lay one egg per day and begin incubation upon clutch completion.

In species with sexual dimorphism, raising female or male offspring may be associated with different costs and benefits, resulting in a skewed nestling sex ratio. We examined the influence of: weather conditions, hatching date and brood size on nestling sex ratio in the black stork Ciconia nigra. We used molecular methods to determine the sex of 284 nestlings. Samples were collected during a 12-years study in central Poland. The overall nestling sex ratio was skewed towards females (61%), which are smaller, and presumably easier to raise than males. Delayed hatching date significantly increased the proportion of female nestlings. Warmer temperatures in the pre-breeding season were correlated with lower proportions of males. This is probably mediated by the influence of weather on water levels in black stork foraging sites. The second most important weather trait was total rainfall in May, the month in which the majority of nestlings hatch. Total May rainfall was negatively correlated with the percentage of male offspring. We used blood haemoglobin concentration as an indicator of body condition in a subsample of 122 nestlings. The males from the study population had lower blood haemoglobin concentrations, indicating their poorer body condition and supporting the hypothesis that they are the more vulnerable sex. We also observed that blood haemoglobin concentration of nestlings is lower in late broods. Deteriorating body condition of late offspring can explain the observed increase in female nestling proportions in delayed broods.

In seasonal environments, a temporal decline in breeding performance (e.g. clutch size, nestling condition, and fledging success) of altricial bird species is a well-known phenomenon. In this study, we present the effect of laying phenology on the physiological condition of nestling great tits (Parus major) in 14 consecutive breeding seasons. We used blood haemoglobin and baseline glucose concentrations as indicators of nestling physiological condition. Nestling blood haemoglobin reflects food base quality and availability during the breeding period. Blood glucose concentration can be used as a supplementary reverse index of condition, since it is negatively related to environmental quality. It might be indicative of the stress caused by unfavourable extrinsic factors, though, due to potential confounding factors such as adverse weather conditions, low food quality, or feeding interruptions, glucose levels should be used in this ecological context with caution. Great tit nestlings from earlier broods were characterised by higher mean haemoglobin concentrations, indicating a seasonal decline in food quality and availability. The blood glucose concentration displayed an opposite pattern, with nestlings from earlier broods being characterised by lower mean concentrations than those from later broods. However, very little of the variation in blood glucose concentration can be explained by the variation in laying date, which suggests that blood glucose concentration is of little importance in the context of breeding phenology. Our results show that the physiological condition of nestlings of this species decreases as the breeding season progresses, most probably due to environmental factors.

The vegetation structure surrounding nest sites is a crucial component of habitat quality and may have large effects on avian breeding performance. Habitat quality reflects the extent to which the environmental characteristics of an area correspond to the preferred habitat characteristics of the species. The concentration of haemoglobin is considered a simple biochemical indicator of nestling body condition. We present results concerning the effects of variation in habitat characteristics on the concentration of haemoglobin in the blood of 14-day-old nestlings and breeding success of European Pied Flycatchers ( Ficedula hypoleuca) in a mature mixed deciduous forest in central Poland. The haemoglobin concentration of nestlings was higher when there were more native oaks and deciduous, native trees on the territory. Breeding success was reduced by the number of alien oak (the Red Oak, Quercus rubra) and other alien deciduous trees, but increased by the number of native oaks in the territory. This study was conducted on only one site so further research is needed to examine the broader applicability of our results. Our data support the idea that haemoglobin concentration may serve as a simple indicator of body condition in nestlings and is useful in field ecophysiology studies of European Pied Flycatchers.

Climate warming affects trophic interactions in ecosystems, which has been documented for relationships between plants, herbivores and predators, including their relative densities, varying between taxons/guilds. In the case of leaf-eating caterpillars feeding in tree canopies the use of caterpillar frass fall as an indicator of density and production has proven to be advisable. Here we analysed annual variation in the peak mass of caterpillar frass fall and the timing of the occurrence of the peak mass in a deciduous forest site as compared with an urban park site during 16 consecutive years (2003–2018) in central Poland. Variation in the mean date of the frass fall peak mass among years was extensive, up to 20 days, with the sequence of the occurrence in the study habitats differing between years. There was a significant advance in the date of the peak frass fall in the course of the study years. There was also great variation in the peak frass fall mass between years and study sites. The tree canopy caterpillars were consistently less numerous in the urban park than in the deciduous forest. Cyclical outbreaks of caterpillars, whose signs were visible in the data set, possibly tended to decline. A decline in the annual peak mass of frass fall over the study period was found. No evidence for synchronization of the timing of blue tit Cyanistes caeruleus breeding with the timing of peak caterpillar abundance was found. The annual average peak mass of caterpillar frass fall proved to be a significant predictor of the annual mean number of fledgling blue tits per brood. Both the consistent pattern of spatio-temporal variation in the timing of peak availability and the abundance of tree-canopy caterpillars and the effects of caterpillar abundance on an insectivorous bird confirm that frass fall is a useful indicator of tri-trophic links to birds that prey upon caterpillars.

Nestling diet and parental provisioning rate are important determinants of reproductive success and future offspring performance in birds. The diet of Black Stork (Ciconia nigra) nestlings was characterized and tested for intra-seasonal and brood-size dependent variation in the type and mass of prey provisioned to the brood. Data were collected on 576 prey items from 45 Black Stork broods in central Poland during 2005–2016. Black Stork nestlings were provisioned almost exclusively with fish and amphibians; the proportion of invertebrates in their diet was marginal. Fish were a dominant component of nestling diet, comprising up to 65% of prey items and over 85% of total prey mass. Common spadefoot tadpoles (Pelobates fuscus), weatherfish (Misgurnus fossilis) and Prussian carp (Carassius gibelio) were among the most abundant prey. Black Storks foraged on relatively small prey, with an average length of 101.4 ± 1.5 mm (n = 576) and an average mass of 13.8 ± 1.0 g (n = 550). Larger broods were significantly more often fed with amphibians and with lighter prey. As the season progressed, the probability of preying on amphibians increased. This study provides evidence for Black Stork provisioning effort optimization mediated by selection of smaller, but easier to catch and handle prey, such as common spadefoot tadpoles.

In oviparous taxa such as birds, clutch characteristics (e.g. egg size, egg mass and the number of eggs) can be considered as energetic investment in reproduction. In this paper, we study variation in the principal component indices of egg size and shape in Rufous Bush Chats (Cercotrichas galactotes) breeding in date palm plantations in the Al Amri Oasis, north Algeria, in 2008–2009 and 2011–2013. For descriptive and comparative purposes, we also present characteristics of egg length, breadth, volume, shape and mass. The size and shape indices as well as dimensions and masses of the eggs laid by particular females tended to be similar to one another, with most variation occurring between clutches (significant repeatabilities for all egg traits). Variation in the size of eggs was influenced by the year-laying date interaction, while variation in the shape (elongation) of eggs was marginally significantly affected by the year-laying date interaction. Year had a significant factor effect on the size of eggs. We also found that hatching success was affected by interactions between year and egg size and shape principal components, thus confirming the existence of fitness-related consequences of variation in the traits of Rufous Bush Chat eggs. Notably, we found that in some years hatching success increased with the elongation of eggs.

Variation in ambient temperature affects various life stages of organisms. It has been suggested that climate change not only implies higher global temperatures but also more unpredictable weather and more frequent extreme weather events. Temperature has a major influence on the optimal laying-incubation-hatching dates of insectivorous passerines, because it poses energetic constraints and affects the timing of food abundance. We have been studying breeding characteristics of great tits Parus major and blue tits Cyanistes caeruleus in two areas, an urban parkland and a deciduous forest, around the city of Łódź since 2002. During the egg-laying period in 2017, both tit species at both study areas faced an unusual cold spell as reflected by a sudden decrease in the mean ambient temperature to ca. 2–3 °C for about 5 days, which caused mean hatching delays of up to 6 days. Since flexibility of behavior plays a major role in adjusting to unpredictable weather conditions, examining its limits may be an important goal for future research.

Partial mortality in broods of altricial passerines results from various reasons, including deficiency of resources, inadequate parental care, diseases and other external factors. In this study we test two hypotheses concerning the phenomenon of partial mortality in nestling altricial passerines: (1) non-adaptive starvation hypothesis based on the assumption that partial brood losses are caused by starvation and undernourishment and has no adaptive value, and (2) adaptive starvation hypothesis assuming that losses from starvation might be elements of an adaptive strategy of reducing surplus nestlings in broods that are over-large. To test the above hypotheses we divided broods of two tit species Great Tit Parus major and Blue Tit Cyanistes caeruleus into two categories: broods with incomplete, less than 100% fledging success and broods with complete 100% fledging success. Subsequently, we compared physiological performance of nestlings between brood categories using blood hemoglobin concentratio...

Birds have specific habitat requirements during the breeding period. The Blue Tit Cyanistes caeruleus is a species evolutionarily associated with forest areas that prefers deciduous and mixed forests, whilst its breeding in urban areas is a relatively recent phenomenon. Long-term data (2002–2015) on reproductive performance (number of hatchlings, hatching success, number of fledglings and fledging success (fledging success as the number of fledglings in relation to the number of hatchlings)) were quantified for two Blue Tit populations in two, floristically and structurally contrasting areas (a mature deciduous forest and an urban parkland) in central Poland. The principal aim of this study is to see whether the habitat type, year or the food availability affect the breeding success of Blue Tits. Forest Blue Tits produced significantly more hatchlings (9.82 ± 2.64 (SD) in the forest vs.9.17 ± 2.16 in the parkland) and fledglings (9.18 ± 2.84 in the forest vs. 8.14 ± 2.68 in the parkland) than urban Blue Tits. The number of fledglings was positively correlated with the number of hatchlings in both study areas. Both forest and urban Blue Tits shared a similar hatching success (85.9 % in the parkland and 85.5 % in the forest), while the fledging success was significantly higher in the forest (83.4 % in the parkland and 86.1 % in the forest). The amount of caterpillar frassfall was also studied (caterpillars are the optimal food for nestlings) at both study areas and it suggested that caterpillars were more abundant in the forest than in the parkland (the maximum amount of frassfall, averaged 0.21 ± 0.11 g frass/m2/day in the urban parkland and 0.59 ± 0.50 g frass/m2/day in the forest in 2003–2015). In the forest area, the mean number of fledglings tended to be related to the amount of frassfall but in the parkland, this relation was non-significant. The long-term dynamics of fledging success in our study sites seems to be mutually independent. Thus low fledging success in the forest site does not mean similarly low fledging success in the urban parkland site and vice versa. We suggest that food availability is one of key drivers of differences in the tits breeding success between both studied habitats.

We studied clutch size and timing of breeding of Rufous Bush Chats Cercotrichas galactotes inhabiting Date Palm plantations in an oasis in NE Algeria with respect to interannual variation. Although oases may be assumed to provide relatively stable ecological conditions favourable for some insectivorous birds, including Rufous Bush Chats, we found relatively high year-to-year variation in the life history traits analysed. In general, clutch size was negatively related to the egg-laying date, with this relation differing between years. This suggests that clutch size was probably determined by a combination of within-year and between-year factors partly operating through the timing of reproduction. The most important of these factors were probably the amount of rainfall and year-to-year growth of palm trees.

Plasma biochemistry values are useful tools for ecophysiological research of birds and other vertebrates. They provide data on the physiological and nutritional state of individuals in various life stages. We predicted that blood triglyceride levels correlate with nutritional state of birds and that this trait is temporally variable. Therefore, we studied the effects of year and distinct habitat type (urban parkland vs woodland) on triglyceride concentration in the blood of nestling Blue Tits Cyanistes caeruleus. We ascertained both seasonal and inter-habitat variation within the trait. Specifically, (1) nestlings from trophic rich forest site were characterised with significantly higher mean triglyceride levels, and (2) mean triglyceride content was significantly higher in one out of three breeding seasons. These results suggest that the studied trait may be used as a robust indicator of habitat trophic abundance and quality.

Abstract The blue tit (Cyanistes caeruleus) is one of a few known passerine birds that incorporate fresh fragments of aromatic plants in their nest during the nesting period. In this study, we experimentally tested whether aromatic plants in blue tit nests affect physiological condition of nestlings as indicated by hemoglobin and glucose in the blood. Nestlings in nests supplemented with fresh, aromatic plants had elevated blood hemoglobin, and therefore improved physiological condition, as compared with control nestlings. There was no difference between nestlings in two contrasting habitats (urban parkland and forest). Although mean levels of blood glucose did not differ between treatment and control nestlings, the blood of forest nestlings contained more glucose than the blood of parkland nestlings, which indicates poorer health for forest nestlings. In general, knowledge of the effects of incorporating fresh green, aromatic plant material into avian nests on physiological condition of nestlings is still fragmentary and more experimental studies are needed. Significance statement The blue tit is one of a few known passerine birds that incorporate fresh fragments of aromatic plants in their nest during the nesting period. Little is known about the impact of this material on nestling body condition, and there is a need to understand this behavior and its effects. We tested whether nestlings in nests supplemented with fresh, aromatic plants improved their physiological condition in comparison with control nestlings. The experiment showed that nestlings from supplemented nests improved their physiological condition by exhibiting elevated hemoglobin.

Haematological and blood chemistry variables are widely used in ecophysiological research as physiological indices of body condition in various vertebrate taxa. In this study, we analysed relationships between blood glucose and blood haemoglobin concentrations of adult birds in wild populations of Blue Tits ( Cyanistes caeruleus) and Great Tits ( Parus major) during the breeding season in central Poland. We found that blood glucose and blood haemoglobin concentrations are negatively correlated. We also show that individual Blue Tits have higher mean haemoglobin levels adjusted for the common value of glucose concentration than individual Great Tits and that females of both species have higher mean haemoglobin concentrations than males. Our results suggest that haematological as well as biochemical variables may be used in tune as complementary indices of body condition in wild bird populations.

Urbanization affects the ecological and behavioral traits of various species of animals, including birds.We present results concerning long-term fluctuations in breeding densities of nest-box populations of the Blue Tit Cyanistes caeruleus and the Great Tit Parus major in two, structurally and floristically contrasting types of habitat (an urban parkland and a rich deciduous forest) located 10 km apart, in central Poland. This study was conducted in 1999–2012 in the parkland site and in 2002–2012 in the forest site. We found a strong correlation of year-to-year changes in breeding densities of Great Tits between the parkland site and the forest site and a lack of such a correlation in Blue Tits. Breeding densities of Great Tits were much higher in the parkland than in the forest area every year during the study period. Annual changes in breeding densities were not correlated between the species studied. The North Atlantic Oscillation Index (NAO-winter index) tended to influence the density dynami...

The placement and size of birds’ nests may have direct consequences for their breeding success. Here, we examined if the location and design of Rufous Bush Chat ( Cercotrichas galactotes) nests influenced their breeding success in the Al Amri Oasis, at the base of Saharan Atlas, north Algeria, in 2008–2009 and 2011–2013. The mean height of nests above ground level was 2.26 ± 0.09 (SE) m, ranging from 0.5 to 4.9 m and the mean nest-cup volume was 246.60 ± 11.82 (SE) cm3, ranging from 102.95 to 471.24 cm3. Nest-cup volumes were positively associated with the height of nests and breeding success was strongly positively associated with the height of nests above ground level. We conclude that pairs of Rufous Bush Chats that bred in higher nests had higher levels of breeding success because they suffered lower predation rates from ground-based predators than lower nests. Lower nests, which are more vulnerable to ground-based predators are likely to be smaller in order to make them less visible to visually searching predators and may also fit more snugly into the smaller leaf stems of smaller palms. These findings agree with the hypothetical predictions based on the properties of palm physical structure as a support for nests, the tree size structure of plantations and the risk of predation.

Many avian species in Europe breed earlier as a result of higher temperatures caused by global climate changes. Climate change means not only higher temperatures but also more frequent extreme weather events, sometimes contrasting with the long-term trends. It was suggested that we should look closely at every extreme phenomenon and its consequences for the phenology of organisms. Examining the limits of phenotypic plasticity may be an important goal for future research. Extremely low spring temperatures in 2013 (coldest spring in 40 years) resulted in birds laying unusually late, and it was followed in 2014 by the earliest breeding season on record (warmest spring in 40 years). Here, we present results concerning breeding phenology and double-broodedness in the Great Tit (Parus major) and the Blue Tit (Cyanistes caeruleus) in 2013 and 2014 in an urban parkland and a deciduous forest in central Poland. Great Tits started laying eggs 18.2 days later in 2013 than in 2014 in the parkland, whereas the analogous difference was 21.1 days in the forest. Blue Tits started laying eggs in the parkland 18.5 days later in 2013 than in 2014, while the analogous difference was 21.6 days in the forest. The difference in the proportion of second clutches in Great Tits between 2013 (fewer second clutches) and 2014 (more second clutches) was highly significant in the parkland and in the forest. This rather large extent of breeding plasticity has developed in reaction to challenges of irregular inter-annual variability of climatic conditions. Such a buffer of plasticity may be sufficient for Blue Tits and Great Tits to adjust the timing of breeding to the upcoming climate changes.

A major function of birds’ nests is to protect eggs and offspring against temperature fluctuations. Reproductive performance was found to be closely related to nest characteristics in some species. We present results concerning nest attributes and their impact on breeding characteristics in Blue Tits ( Cyanistes caeruleus) and Great Tits ( Parus major) in central Poland over a three year period, 2012-2014, in an urban parkland and a deciduous forest. In Blue Tits, hatching success was positively affected by the nest lining mass. Clutch size was associated with the lining mass and nest mass, and the number of hatchlings was associated with both the nest mass and lining mass. In Great Tits, hatching success was positively affected by the lining mass and fledging success was positively affected by the nest depth and nest mass. Also, clutch size tended to be related to the nest depth and the number of hatchlings was associated with the lining mass. We found that Blue Tit nests were deeper and heavier than Great Tit nests. There were no differences in nest depth and nest mass between two habitats for both tit species. We conclude that there is a relationship between better quality nests and better breeding performance in both Great Tits and Blue Tits.

This study applies a field experimental approach to an issue of single lead exposures and their effects on specific haematologial indices in nestling songbirds. We used nestling great tits Parus major as a model and showed that higher lead exposure was associated with significant haematocrit decline. In contrast, the assessment of the H/L ratio revealed no significant effect of a single lead exposure., Lead (Pb) is recognized as one of the most toxic trace elements that can induce a wide range of negative health effects in wildlife. Because the investigation of basic environment-sensitive physiological indicators is easy to perform in wild birds, they have been considered as valuable bioindicators of lead contamination. The harmfulness of lead poisoning can depend on the type of exposure, and in most studies of birds, an effect of chronic lead exposition has been considered. In this study, we investigated whether a single exposure to specific doses of lead affected such physiological indices as haematocrit and the heterophil-to-lymphocyte ratio (H/L ratio). For this purpose, we conducted an experiment based on intentional lead supplementation, with the use of two different doses, applied to randomly chosen great tit (Parus major) nestlings from randomly selected broods. A few days after the exposure (when the nestlings were 15 days old), we determined haematocrit and the H/L ratio as potentially sensitive physiological indicators of lead intoxication. We found that the treatment with lead resulted in a significant decline in haematocrit level. In addition, we found that the age when lead exposure occurred can be considered as an important factor influencing haematocrit variation. A decrease in haematocrit was observed on consecutive days of nestling life. In contrast, the H/L ratio did not show any significant response to lead exposure. These results clearly show that the assessment of haematocrit level for nestling great tits can provide a simple and rapid method of indirect evaluation of physiological effects of lead intoxication caused by a single exposure.

Life-history theory suggests that macro- and micro-parasites may generate selection pressures by affecting host health. In the present study, we replaced natural great tit Parus major nests in two, structurally and floristically contrasting sites. Nestlings that were developing in treated nests improved physiological health status in comparison with control nestlings., Most passerines use nests as the exclusive place to lay and incubate eggs and bring nestlings up to fledging. Nests of secondary cavity nesters, like tits, provide a moist, warm and protected habitat for reproduction of blood parasites. Offspring fitness depends on interactions between parental care and environmental constraints. Life-history theory suggests that macro- and micro-parasites may generate selection pressures by affecting host health. In the present study, we replaced natural great tit Parus major nests in two, structurally and floristically contrasting sites (an urban parkland and a rich deciduous forest, located 10 km apart in Łódź, central Poland), with fresh, sterilized, artificial moss-cotton wool nests, twice, on the fifth and tenth day of nestlings life. We then examined haematological condition indicators (haemoglobin and glucose concentrations) of about 14-day-old nestlings. Nestlings that were developing in treated nests improved their health status in comparison with control nestlings. The mean haemoglobin and glucose concentrations (treated and control) also varied between both study areas. Our study confirms that the level of haemoglobin and especially the level of glucose may be treated as reliable indicator of environmental characteristics in great tits.

Numerous studies from different locations in Europe show that nest-box populations of tits in urban areas lay earlier and produce fewer eggs than do tits in rural areas. We collected data on laying dates and clutch size in two great tit Parus major populations nesting in oak deciduous forest and urban parkland areas, only about 10 km apart, in central Poland over 11 years. The abundance of caterpillars, the optimal food of breeding tits, at both breeding areas was also quantified. We analysed long-term trends in the timing of egg laying and clutch size. We focused on the effects of year, habitat type, insect availability and weather conditions shortly before egg laying on the patterns of variation in laying date and clutch size. In general, our study supports earlier generalisations on urban and rural tit populations. In particular, our finding that great tits initiated breeding consistently earlier in the urban site than in the forest area supports earlier studies on urbanised birds. The mean laying date was strongly and negatively associated with air temperature between 15 March and 15 April in both habitats. Mean clutch size was lower in the parkland than in the forest population, at least partly in response to the greater abundance of caterpillars in the forest. A novel result of this study is that clutch size differed between habitats to a varying degree in different years, in association with a stronger response to caterpillar abundance in the forest than in the park. Clutch size tended to decline with the progress of the breeding season within years in the parkland site, especially in “early years”, but not in the forest habitat.

Amount and quality of resources may be variable and generally poor in habitats of marginal avian populations living at the edge of species breeding range. We studied variation in egg traits (length, breadth, volume and shape) in three populations of the African Blue Tit Cyanistes caeruleus ultramarinus inhabiting degraded habitats in highlands of Algerian Saharan Atlas at mean altitudes 1328–1437 m a.s.l. We found high within-clutch repeatability of all the egg traits studied. As theoretically expected in peripheral parts of the species geographic range, there was considerable variation in egg-size traits among the study populations, with eggs being distinctly smaller and more elongated at a site characterised by most human-modified habitat composed of maquis scrubland with rare Pistacia trees. Egg length and shape tended to be affected by the altitude of nest site and by clutch size, but not laying date. We found some effects of egg traits on hatching and fledging success, suggesting that fitne...

We examined the variation in the date of the onset of egg laying and clutch size in three peripheral populations of the Afrocanarian Blue Tits Cyanistes teneriffae ultramarinus at the edge of the species and subspecies geographic range. This study was carried out in three study sites, 130–290 km apart, in similar geographic conditions of the South Border Range of the Saharan Atlas in Algeria. Mean altitudes of nesting territories were between 1327 and 1437 m a.s.l. Habitats of the study sites were covered by the secondary, human-modified vegetation, ranging from a maquis shrubland, with the Holm oak Quercus ilex shrubs to woodlands dominated by the Atlas cedar Cedrus atlantica or by the Aleppo pine Pinus halepensis. 169 wooden nest-boxes were monitored for breeding parameters (laying dates and clutch sizes) during the breeding seasons 2007–2009 and 2011–2013. The timing of egg laying was relatively late for the latitude of the study sites, with overall mean laying dates varying between the study ...

The main aim of this study was to examine if blood glucose concentration displays any pattern of variation between years and distinct habitats. Bird blood glucose concentration reflects their high metabolic demands and is influenced by a variety of environmental factors. Therefore variation in glucose levels of free-living birds is an important aspect of their functional ecology. We now present results concerning variation in glucose concentration in the blood of Great Tit ( Parus major) nestlings (∼ 14-day-old). We also compare the obtained results with variation in blood glucose nestlings Blue Tit ( Cyanistes caeruleus) published elsewhere. Our present study was conducted in central Poland in an 8-year period, 2005–12 in two distinct habitat types: an urban parkland and a rural deciduous forest. The most important findings of the study were: (i) mean levels of blood glucose varied markedly between years; (ii) glucose concentrations were significantly higher in the parkland study area; (iii) heavier nestlings were characterised with lower blood glucose levels; (iv) there was a negative relationship between fledging success and per-brood mean glucose concentration in the urban park site but not in the forest site; and (v) Great Tit nestlings were characterised by significantly higher blood glucose levels than Blue Tits nestlings. Variation in glucose concentration of nestling Great Tits shows a consistent spatio-temporal pattern which is generally similar to that found in Blue Tits.

Haematological indices have been frequently used to investigate the physiological condition of wild birds. In this respect, among many blood parameters, haematocrit has been considered to be a valuable indicator. Many studies, mostly conducted on adult birds, have discussed possible causes of haematocrit variation, pointing out several factors both natural and anthropogenic as being crucial. In this study, we examined the level of haematocrit for Blue Tit Cyanistes caeruleus nestlings in relation to habitat type and inter-year sources of variation. We found that the haematocrit of Blue Tit nestlings varied significantly between study years, showing an increasing trend. We explain this variation by changeable weather conditions, pointing out that temperature is a possible factor. The increase in haematocrit in subsequent study years was accompanied by a decline in the ambient temperature. No significant effect of habitat type was noted in the haematocrit variation. We also found that haematocrit values tended to be positively associated with fledging success. All this confirms that haematocrit may be reasonably used as a one of the indicators of nestling condition.

Sequentially laid eggs of small songbirds are built from the current income of resources and therefore can be subject to different environmental influences on the short-term and long-term time scales. In this paper we study variation in egg length, breadth, volume and shape in Pied Flycatchers Ficedula hypoleuca in Łodź, central Poland, during 2002–2012, in relation to climatic and habitat-related factors. We found a significant decreasing trend in egg length, breadth and volume across the study years and a slight tendency for eggs to be a little more elongated in a forest site than in an urban parkland site. Even though mean monthly temperature in May is known to have increased since the 1970s in the area of Łodź, the average ambient temperature during the time of formation of eggs in particular clutches tended to decrease, with increasing variability at the same time, in 2002–2012. Egg size traits showed a positive association with average temperature and a negative relation with variability i...

Black stork nestlings were measured (wing, bill, head, and tarsus lengths) at weekly intervals in central Poland in 2012, 2014, and 2015. The aim of the study was to provide growth equations based on nestling measurements to allow age estimation of black stork nestlings. The hatching hour and date of nestlings in five nests were determined using trail cameras. The age of the measured nestlings ranged from 18 to 53 days. Wing, bill, and head lengths showed linear growth, while tarsus growth was only linear for nestlings not exceeding 35 days old. Within the age range studied, wing length grew 9.6 mm per day, head length grew 2.3 mm per day, and bill length grew 1.8 mm per day. The study provides the first growth parameters for the black stork.

Most passerines use nests as the exclusive place to lay and incubate eggs and bring nestlings up to fledging. Nests of secondary cavity nesters, like tits, provide a moist, warm and protected habitat for reproduction of blood parasites. Offspring fitness depends on interactions between parental care and environmental constraints. Life-history theory suggests that macro- and micro-parasites may generate selection pressures by affecting host health. In the present study, we replaced natural great tit Parus major nests in two, structurally and floristically contrasting sites (an urban parkland and a rich deciduous forest, located 10 km apart in Łodź, central Poland), with fresh, sterilized, artificial moss-cotton wool nests, twice, on the fifth and tenth day of nestlings life. We then examined haematological condition indicators (haemoglobin and glucose concentrations) of about 14-day-old nestlings. Nestlings that were developing in treated nests improved their health status in comparison with control nestlings. The mean haemoglobin and glucose concentrations (treated and control) also varied between both study areas. Our study confirms that the level of haemoglobin and especially the level of glucose may be treated as reliable indicator of environmental characteristics in great tits.

Egg size is a basic species-specific life-history trait in birds which influences offspring performance through the nestling stage and, therefore, fitness. Shells of snails are the principal source of calcium for female parids and some other passerines during egg formation. Shortages in the availability of snail shells may lead to laying smaller eggs with thinner shells. In urban green spaces that require protection against pests, the numbers of snails may become greatly reduced in response to molluscicide treatments. The use of a molluscicide treatment against pest slugs in the Botanic Garden, Łodź, Poland, in 2013 and 2014 provided a unique quasi-experimental setting to study the effect of molluscicide on both non-target snails and Blue Tit Cyanistes caeruleus eggs. Using a forest study site where no treatment was applied as a control area, we tested for effects of the molluscicide treatment in the Botanic Garden on the density of snails and on the egg volume of Blue Tits. We found that after the molluscicide treatment a dramatic drop in snail numbers occurred, which likely restricted the availability of snail shells for egg laying Blue Tits in the Botanic Garden. Correspondingly, egg sizes significantly decreased in the Garden, while they stayed constant over time in the forest. Eggs in bigger clutches were more strongly affected by the molluscicide treatment than eggs in smaller clutches. Our quasi-experimental study suggests that Blue Tits are sensitive to poor availability of snail shells. This is manifested by laying smaller eggs, which require less calcium to be incorporated in the eggshell, in response to a dramatic drop in the availability of snail shells. This result is expected to raise awareness of potential indirect and inadvertent effects of park pest management on biota other than molluscan pests.

In this study, we examined heavy-metal concentrations in feathers of nestling great tits Parus major and blue tits Cyanistes caeruleus at two different sites (urban parkland vs. deciduous forest) located in the Łódź agglomeration in relation to interyear variation. We found that tit species did not differ significantly in lead and cadmium concentrations. Zinc concentration was significantly higher in blue tits. We also found that lead and cadmium levels in blue tit nestlings and the level of lead in great tit nestlings were higher in the parkland site than in the woodland site. We explain habitat variation in heavy-metal concentrations in feathers of nestlings by different levels of contamination at study sites. For both tit species, significant variation in heavy-metal amounts accumulated by nestlings was found between years with the lowest value in a year with the lowest value of rainfall. We suggest that the interyear variation may be accounted for by differences in rainfall, thus influencing quantities of trace elements bioavailable in the environment.

The major aim of this study was to examine the influence of the European Pine Marten ( Martes martes) predation on the heights of nests of Blue Tits ( Cyanistes caeruleus) and Great Tits ( Parus major) in nestboxes of different security levels. To this end we performed a comparison of nest heights before and after introducing an anti-predator device to two size-types of wooden nestboxes set up in a deciduous forest. Blue Tit and Great Tit nest sizes were influenced by the application of plastic entrance tubes as anti-predator devices that elongated a distance between the entrance and the interior of the nestbox. Nests were taller in nestboxes equipped with anti-predator devices regardless of nestbox size. Nests located in smaller nestboxes were destroyed by Martens more frequently than nests built in bigger nest boxes. Most nest functions in cavity-nesting birds, such as filling the excessive cavity space, maintenance of proper humidity, thermal, light and sanitary conditions for eggs and nestlings, improve with nest sizes. Because, in contrast, the risk of nest predation by martens increases with nest size (height within the nestbox), the nest predation constitute a major factor that constrains cavity-nesting birds in constructing tall nests.