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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 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.

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.

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...

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.

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...

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.

Enduring changes in the surrounding environment cause long-term stress in birds, which can affect the activity of the immune system and lead to changes in heterophil-to-lymphocyte ratios (H:L). The aim of this paper is to investigate if the H:L ratios of male and female Great Tits Parus major during the first breeding attempt differ between two sites of dissimilar habitats – an urban parkland site and a deciduous forest site. In the final model we found a difference between sites, while separate submodels for the study sites showed that females had higher H:L ratio than males in the urban parkland site, with the opposite result being found in the forest site. We suppose that the pattern of variation in H:L ratios we found may result from greater parental expenditures of females as compared to males. Such difference in the H:L ratio between habitats could be the reason for the substantial difference in trophic conditions between the forest and park areas during the breeding of tits.

Permanent changes in the surrounding environment cause long-term stress in birds, which, when lasting days or weeks, affects the activity of the immune system and increases susceptibility to diseases, leading to changes in the levels of haematological parameters. The heterophil-to-lymphocyte ratio (H:L-ratio) is generally considered an independent and robust indicator of stress level in birds. This parameter allows in a simple way to evaluate activity of the immune system and individual health state of adult and nestling birds. It also enables assessing a body response to short- and long-term stress induced by, among others, the surrounding environment, social stress, blood parasites or a greater energy expenditure of females during breeding. Under conditions of field work the determination of the H:L-ratio is not difficult because what is only needed to conduct a blood smear test is a drop of blood that can be easily obtained even from birds of a small body mass. Moreover, an increase in the H:L-ratio is observed after about an hour from the moment of catching a bird contrary to other measurements like the determination of a baseline level of corticosterone.In this article available literature that discusses the impact of various factors on the H:L-ratio in the Great Tit as a species of ‘fast-paced’ life is reviewed. In adult and nestling birds the H:L-ratio is influenced by various factors — ecological and ecophysiological ones. In some cases the same factor, e.g. brood size manipulation or a type of habitat, can significantly influence the level of the discussed stress indicator as well as it may not show any impact at all. While interpreting the H:L-ratio one must take into account an impact of various ecological and ecophysiological factors on health state, such as habitat, phase of the annual cycle, differences between brood attempts, sex, age as well as on relations with other indicators of condition e.g. body mass or total blood haemoglobin concentration.

The aim of this study was to determine the possibility of using feathers of blue tit nestlings to assess the level of endogenous accumulation of lead. For this purpose we conducted an experiment with lead application to randomly chosen nestlings from eight randomly drawn broods. Five days after the exposure, feathers of lead-treated nestlings had significantly higher lead concentrations than control nestlings. This result suggests that feathers can be used as reliable non-destructive bioindicators to assess the level of heavy metals originating from contaminated food, which is of great significance for comparative studies on ecological consequences of pollution.

Physiological functions of growing nestlings are thought to be traded-off in relation to rearing conditions, with the resulting physiological state of fledglings having important long-lasting consequences for their fitness. By manipulating brood size up and down, and, separately, by supplying additional food (mealworms — larvae of Tenebrio molitor) we tested if alterations of the rearing conditions would influence nestling performance in Blue Tits Cyanistes caeruleus and Great Tits Parus major. Brood size manipulation affected body mass, heterophil-to-lymphocyte ratio (H:L) and fledging probability in both species and the level of triglycerides in nestling Great Tits. Extra food supply influenced only fledging probability, with no other effect on indicators of nestling performance. An effect on nestling body mass and a lack of effect on cell-mediated immune response in the brood-size experiment suggest that nestlings in enlarged broods sacrificed growth to maintain immunity. In general, effects ...

High metabolic rates of birds demand an efficient oxygen transport system; this is ultimately based on the oxygen carrying capacity of haemoglobin. Therefore patterns of variation in blood haemoglobin content of wild birds are an important aspect of functional ecology. In this paper we report results concerning variation in haemoglobin con- centration in the blood of adult Blue Tits Cyanistes caeruleus and Great Tits Parus major during the nestling rearing peri- od (days 7-15 of nestlings life) of first broods in central Poland in 2003-2009. The most important findings of this study are: (i) average haemoglobin concentration in blood differs between Blue Tits and Great Tits, with higher values in Blue Tits; (ii) males differ from females in both these species, with higher values in females, and (iii) there is also significant variation among years, with parallel tendencies for both species. We explain the patterns of haemoglobin content vari- ation in adult tits by differences in metabolic demands for oxygen transported by blood. The demands are higher for the smaller-bodied species (Blue Tits), heavier working sex (females) and in years with worse physical and trophic con- ditions, though only non-significant relationships with weather conditions (temperature and rainfall) or food availabil- ity (measured by frassfall) were found during our long-term study.

Amount of food supplied to nestlings by their parents is considered to affect the development of nestling physiological condition. In this study we supplied parental Great Tits Parus major with extra food, larvae of Tenebrio molitor, put into feeders close to nest-boxes, assuming that this should facilitate parental care and, as a consequence, nestling nutrition. The following nestling characteristics measured 13 days after hatching were analysed: body mass, haematocrit, blood concentrations of haemoglobin, glucose and triglycerides, heterophil-to-lymphocyte ratio (H/L), and patagium swelling after PHA injection. Nestlings from extra food broods were significantly heavier than control ones. They also had lower H/L, which indicated lower stress. No other variable was significantly affected by the experiment. Possibly, the rainy weather and non-restrictive natural trophic conditions during the experiment caused weakening of the net benefits from extra food.

Wild passerines, especially tits, utilize snail shells as the main source of calcium necessary for laying females to construct egg shells. This research found that the two study areas, representing two habitat types — a mature decid- uous forest and a human-disturbed parkland — are inhabited by different snail assemblages: both species richness and density are much higher in the parkland than in the forest. This means that less calcium is available to female tits in the forest than in the parkland, which could result in calcium limitation in the former habitat. Egg size traits, i.e. volume, length and breadth, in the Blue Tit show a consistent long-term pattern of variation that reflects the pattern of calcium availability: egg trait values are higher in the parkland than in the woodland. No habitat-related variation in egg size traits was found in the Great Tits. We suggest that the lack of a relation between Great Tit egg characteristics and snail availability results from the higher ecological plasticity of this species in comparison with the Blue Tit, including its abil- ity to exploit alternative sources of calcium.

The physiological condition of nestling altricial birds depends on the quantity and quality of food delivered to them by parents. One indicator of the condition of Great Tit Parus major nestlings is the haemoglobin concentration in their blood. The present study demonstrates the influence of weather conditions (temperature and rainfall) on nestling haemoglobin concentrations during two consecutive breeding seasons in two different habitat types (parkland vs. woodland) in the city of Łodź in Central Poland. This influence probably results from the effects of weather on the trophic base of the Tits. Dry, hot weather strongly affected bush and herbal foliage later in the breeding season (mid-June to mid-July) in 2006, presumably by interfering with the development of herbivorous arthropod populations. This in turn caused food shortages for second broods of Great Tits, which resulted in nestlings having low haemoglobin levels. In the following year, temperature was on average lower, and rainfall was regular but not very heavy. These conditions enabled the development of arthropod assemblages, and the trophic base for birds was much richer. Haemoglobin concentrations in the blood of nestlings from second broods were significantly higher than those of first broods and, unexpectedly, second-brood nestlings in 2007 were on average in better physiological state than first-brood nestlings in 2006 in both habitats. The relationship between haemoglobin concentration, brood category and year was very similar to that for nestling body mass. However, it was independent of both body mass and brood size. In some years and under certain conditions, second broods can be more successful than first broods.

Different aspects of the breeding biology of the Black-winged Stilt were studied in a natural oasis wetland area in the Sahara Desert, the Chott of Ain El Beida, near Ouargla, E Algeria in 2004–2007. In this wetland the water level is independent of rainfall and Stilts start egg laying when average daily temperature increases to ca. 15°C, mostly in April-May, with no significant differences between years. Complete clutches usually consist of 4 eggs but 3 egg clutches happen with low frequency (2.9–5.6%). Egg size traits (mass, length, breadth and volume) tended to decrease from 2004 to 2007, probably due to deteriorating hydrological conditions of the wetland. Within-clutch variability showed both significant repeatability and laying-sequence-dependent differences among eggs, with the final egg being smaller than the clutch mean value. We found that all egg traits studied showed a negative correlation with the date of laying, which seems to be a phenomenon analogous to the seasonal decrease in c...

Producing high quality offspring of good physiological performance, able to survive to independence and, then, to reproductive maturity is a major component of life history strategies. The ability of nestling altricial birds to develop a good physiological condition depends to a large extent on the amount and quality of food provided by par- ents, as well as other aspects of parental care. We hypothesized that experimental changes to the original brood size should affect both parental Blue Tits and their offspring, resulting in corresponding changes in the body condition of the nestlings. Over two breeding seasons, using two habitat sites, we conducted an experiment with two manipulative treatments applied to broods of three-day-old nestlings — the reduction or enlargement of broods by three nestlings, and one non-manipulative control treatment. Our aim was to test whether the experiment would affect a number of different measures of nestling condition: blood concentrations of hemoglobin and glucose, heterophil-to-lymphocyte ratio and morphometric condition index, all being analyzed when the nestlings were 13 days old. We found no effect in the case of hemoglobin, despite the fact that it had previously been shown to be sensitive to large-scale differences in trophic conditions between habitats and years and to the experimental removal of nest parasites. All the remaining variables, i.e. heterophil-to-lymphocyte ratio, glucose concentration and morphometric condition index, responded to the experimental treatments, showing different but reasonable patterns of variation. We suggest that an experimental increase in brood size definitely hinders the development of nestling physiological condition, but even an experimen- tal reduction of broods can affect some physiological indicators (glucose), probably because of readjustments in the feeding rate.

Nutrition during the time spent at the nest is critical for the development of the body condition in altricial birds, including nestling blue tits (Cyanistes caeruleus). Trophic conditions tend to be variable in time and space, which should influence the physiological condition of growing birds. In this paper, we consider haemoglobin concentration as a general indicator of chick physiological condition. Its variation is both consistent within broods and indicative/prognostic of survival from the moment of hatching to fledging. We show that haemoglobin concentration of nestling blue tits is on average higher in years and habitats characterised by rich abundance of caterpillars than under poor caterpillar availability. Haemoglobin seems to quite exactly reflect even relatively subtle differences in trophic conditions.