Sex-biased mortality can occur in birds during development, for example due to sexual differences in energy requirement and/or environmental sensitivity, or the effects of sex hormones or sex differences in the expression of mutations linked to sex chromosomes. The extent of sex-bias in mortality may also be related to environmental conditions that influence offspring development and survival. Urban areas often provide poorer conditions for nestling development resulting in higher offspring mortality compared to natural areas, which may accelerate sex differences in offspring mortality in cities. To test this hypothesis, we examined the sex ratio of dead offspring in Great Tits (Parus major), using 427 samples of unhatched eggs and dead nestlings collected in two urban and two forest sites between 2013 and 2019. The ratio of males in the whole sample of dead offspring (56.9%) was significantly higher than expected by an 1:1 ratio, and the strongest sex biases were detected in urban areas (57.6% males) and in young nestlings (<14 days old, 59.0% males). However, the sex ratios of dead offspring did not differ significantly among study sites and between offspring developmental stages. 29.3% of unhatched eggs contained a visible embryo, and the proportion of embryo-containing unhatched eggs did not differ significantly between urban and forest study sites. These results suggest male-biased offspring mortality in Great Tits, and highlight the need of large datasets to detect subtle differences between habitats and developmental stages.

Sex-biased mortality can occur in birds during development, for example due to sexual differences in energy requirement and/or environmental sensitivity, or the effects of sex hormones or sex differences in expression of mutations linked to sex chromosomes. Urban habitats often provide poorer conditions for nestling development resulting in higher offspring mortality compared to natural habitats, which may accelerate sex differences in offspring mortality in cities. To test this hypothesis, we examined sex-specific offspring mortality in great tits (Parus major), using 660 samples of dead offspring collected in two urban and two forest sites between 2013-2019. Overall, the sex ratio of dead offspring was significantly male-biased (56.80%). When habitats and age groups were analysed separately, the sex ratio of dead offspring was significantly male-biased in urban habitat (57.60%) and in young nestlings (58.62%), and non-significantly in the forest habitat (56.58%) and in unhatched embryos (54.11%) or in old nestlings (54.55%). However, these estimates were associated with wide confidence intervals, thus sex ratios of dead offspring did not differ significantly among study sites and between age groups when these were analysed together. 70.30% of unhatched eggs was not fertilized, and their proportion did not differ between urban and forest habitats. These results suggest male-biased offspring mortality in great tits, and highlight the need of large datasets to detect subtle differences between habitats and developmental stages.

Haemosporidian blood parasites are widely used in evolutionary ecological research when exploring the effects of parasites on different life-history traits of their bird hosts. However, their roles in bird migration are less studied. If these parasites deteriorate the body condition of the birds strongly, they might negatively affect the whole migration phenology and the survival of the birds as well. In our study, we tested the relationships between infection for parasite genera (Haemoproteus or Plasmodium), the three most frequent parasite lineages and body condition (body mass, fat deposit), and the timing of autumn migration in the European Robin (Erithacus rubecula). We found that mean body mass and fat scores did not differ between parasitized and non-parasitized individuals, but infected juveniles arrived later than their non-infected counterparts. The difference in the arrival time of parasitized and non-parasitized birds was greater in the case of Haemoproteus infections. However, when we analysed the effects of the distinct parasite lineages separately, we found that prevalence of parasite lineages correlated with the body mass, fat storage, and timing of autumn migration of the birds in a different direction. Our results therefore emphasize the importance of testing the impacts of the different parasites individually, because possible lineage-specific effects on bird condition during migration might exist.

The ubiquitous activity of humans is a fundamental feature of urban environments affecting local wildlife in several ways. Testing the influence of human disturbance would ideally need experimental approach, however, in cities, this is challenging at relevant spatial and temporal scales. Thus, to better understand the ecological effects of human activity, we exploited the opportunity that the city-wide lockdowns due to the COVID-19 pandemic provided during the spring of 2020. We assessed changes in reproductive success of great tits (Parus major) at two urban habitats affected strikingly differently by the ‘anthropause’, and at an unaffected forest site. Our results do not support that urban great tits benefited from reduced human mobility during the lockdown. First, at one of our urban sites, the strongly (− 44%) reduced human disturbance in 2020 (compared to a long-term reference period) did not increase birds’ reproductive output relative to the forest habitat where human disturbance was low in all years. Second, in the other urban habitat, recreational human activity considerably increased (+ 40%) during the lockdown and this was associated with strongly reduced nestling body size compared to the pre-COVID reference year. Analyses of other environmental factors (meteorological conditions, lockdown-induced changes in air pollution) suggest that these are not likely to explain our results. Our study supports that intensified human disturbance can have adverse fitness consequences in urban populations. It also highlights that a few months of ‘anthropause’ is not enough to counterweight the detrimental impacts of urbanization on local wildlife populations.

Abstract The ubiquitous activity of humans is a fundamental feature of urban environments affecting local wildlife in several ways. Testing the influence of human disturbance would ideally need experimental approach, however, in cities, this is challenging at relevant spatial and temporal scales. Thus, to better understand the ecological effects of human activity, we exploited the opportunity that the city-wide lockdowns due to the COVID-19 pandemic provided during the spring of 2020. We assessed changes in reproductive success of great tits (Parus major) at two urban habitats affected strikingly differently by the ‘anthropause’ and at an unaffected forest site. Although anecdotic observations suggested that urban wildlife may benefit from reduced human mobility during the lockdown, our results do not support this. First, at one of our urban sites, the strongly (-44%) reduced human disturbance in 2020 (compared to a long-term reference period) did not increase birds’ reproductive output relative to the forest habitat where human disturbance was low in all years. Second, in the other urban habitat, recreational human activity considerably increased (+ 40%) during the lockdown and this was associated with strongly reduced nestling body size compared to the pre-COVID reference year. Analyses on meteorological conditions and the lockdown-induced changes in air pollution suggest that these factors are not likely to explain our results. Our study supports that intensified human disturbance can have adverse fitness consequences in urban populations. It also highlights that a few months of ‘anthropause’ is not enough to counterweight the detrimental impacts of urbanization on local wildlife populations.

Since male and female offspring may have different costs and benefits, parents may use sex ratio adjustment to increase their own fitness under different environmental conditions. Urban habitats provide poorer conditions for nestling development in many birds. Therefore, we investigated whether great tits (Parus major) produce different brood sex ratios in urban and natural habitats. We determined the sex of nestlings of 126 broods in two urban and two forest sites between 2012 and 2014 by molecular sexing. We found that brood sex ratio did not differ significantly between urban and forest habitats either at egg-laying or near fledging. Male offspring were larger than females in both habitats. This latter result suggests that male offspring may be more costly to raise than females, yet our findings suggest that urban great tits do not produce more daughters despite the unfavourable breeding conditions. This raises the possibility that other aspects of urban life, such as better post-fledging survival, might favour males and thereby compensate for the extra energetic costs of producing male offspring.

Avian malaria parasites can negatively affect many aspects of the life of the passerines. Though these parasites may strongly affect the health and thus migration patterns of the birds also during autumn, previous studies on avian malaria focused mainly on the spring migration and the breeding periods of the birds. We investigated whether the prevalence of blood parasites varies in relation to biometrical traits, body condition and arrival time in the European Robin (Erithacus rubecula) during autumn migration. We found no sex or age related differences in avian malaria prevalence and no relationship between infection status and body size or actual condition of the birds was found either. However, the timing of autumn migration differed marginally between infected and non-infected juveniles, so that parasitized individuals arrived later at the Hungarian stopover site. This is either because avian malaria infections adversely affect the migration timing or migration speed of the birds, or because later arriving individuals come from more distant populations with possibly higher blood parasite prevalence. The possible delay that parasites cause in the arrival time of the birds during autumn migration could affect the whole migratory strategy and the breeding success of the birds in the next season.

AbstractOrnithological studies often rely on long-term bird ringing data sets as sources of information. However, basic descriptive statistics of raw data are rarely provided. In order to fill this gap, here we present the sixth item of a series of exploratory analyses of migration timing and body size measurements of the most frequent passerine species at a ringing station located in Central Hungary (1984–2017). First, we give a concise description of foreign ring recoveries of the European Robin in relation to Hungary. We then shift focus to data of 40,128 ringed and 11,231 recaptured individuals with 24,056 recaptures (several years recaptures in 313 individuals) derived from the ringing station, where birds have been trapped, handled and ringed with standardized methodology since 1984. Timing is described through annual and daily capture and recapture frequencies and their descriptive statistics. We show annual mean arrival dates within the study period and present the cumulative distributions of first captures with stopover durations. We present the distributions of wing, third primary, tail length and body mass, and the annual means of these variables. Furthermore, we show the distributions of individual fat and muscle scores, and the distributions of body mass within each fat score category.We distinguish the spring and autumn migratory periods and age groups (i.e. juveniles and adults). Our aim is to provide a comprehensive overview of the analysed variables. However, we do not aim to interpret the obtained results, merely to draw attention to interesting patterns that may be worth exploring in detail. Data used here are available upon request for further analyses.

Background: Defining the sex of individual birds can be crucial for scientific studies and captive breeding, as well. However, many bird species (and almost all nestling) can only be sexed via molecular methods. Universal diagnostic primers that can sex most birds are used widely, most commonly those that are based on amplifying differently sized fragments of the CHD1 (Chromo-helicase DNA binding protein 1) gene on the sex chromosomes. Still, little is known about their reliability in several avian orders or in different tissue samples. Objectives: The aim of this research was to test four frequently used universal bird sexing markers in 13 Neognathae bird orders and in different sample types. These markers (P2/P8, 2550F/2718R, CHD1-i16 and CHD1-i9) amplify fragments of intronic regions of the CHD1-Z and CHD1-W genes. Samples of more than 60 bird species and various tissue types (feathers of different sizes, dried and fluid blood) were tested. Amplified CHD1 fragments were visualized with UV light, following agarose gel electrophoresis. Results and Discussion: Our results confirm the universality of these primer pairs in most avian orders, but their application needs some consideration. 21% of the small size feathers gave no detectable results. The marker CHD1-i9 did not work in 14.5% of the feather samples. Such error occurred only in 4% of blood samples. The marker P2/P8 needed the longest electrophoresis time, but did not yield visible sex-specific bands even after 120 minutes in nine species. Similarly, no sex-specific bands were detected with 2550F/2718R in seven species. In CHD1-i16, aspecific bands making sexing diagnosis difficult were common, and even after improving the protocol, four species gave inconsistent results. In conclusion, these four markers can be assumed as near universal, easy-to-use tools for molecular sexing of Neognathae birds, but they all have some limitations. When choosing a marker for molecular sexing, not only the species, but also the tissue sample should be taken into consideration. We suggest to avoid the CHD1-i9 marker when using small or degraded feather samples. P2/P8 is not recommended when the size difference between the two sex chromosome-linked fragments is too small.

In this study, blood samples of 259 Acrocephalus sp. warblers were molecularly analysed for Anaplasmataceae and Rhodospirillaceae based on PCR amplification of 16S rRNA gene fragments. One bird blood sample (from Reed Warbler, Acrocephalus scirpaceus) yielded a sequence with 99.8% identity to Haematospirillum jordaniae. This is the first molecular evidence for the occurrence of this species in the blood of any vertebrate other than human. Another bird blood sample (from Marsh Warbler: Acrocephalus palustris) yielded a Wolbachia sequence, closely related to a moth endosymbiont with 99.8% identity. A nematode origin of Wolbachia DNA detected here in avian blood can be excluded, because results of phylogenetic analysis showed its closest alignment with insect wolbachiae. This is the first finding of insect Wolbachia DNA in the circulatory system of birds, which can be explained either by the inoculation of wolbachiae by blood-sucking vectors, or passing of Wolbachia DNA from the gut into the blood of this insectivorous bird species.

Abstract Ornithological studies often rely on large temporal scale ringing datasets as source of information. However, basic descriptive statistics of collected data are rarely provided. In order to fill this gap, here we present the first item of a series of exploratory analyses of migration timing and body size measurements of the most frequent Passerine species at a ringing station located in Central Hungary (1984–2015). First, we give a concise description of foreign ring recoveries of the Pied Flycatcher in relation to Hungary. We then shift focus to data of 2860 individuals deriving from the ringing station, where birds have been trapped, handled and ringed with standardized methodology since 1984. Timing is described through annual and daily capture and recapture frequencies and their descriptive statistics. We show annual mean arrival dates within the study period and we present the cumulative distribution of first captures with stopover durations. We present the distributions of wing, third primary, tail length and body mass, and the annual means of these variables. Furthermore, we show the distribution of individual fat and muscle scores, and the distribution of body mass within each fat score category. We distinguish migration periods (spring and autumn), age (i.e. juveniles and adults) and sex groups. Our aim is to provide a comprehensive overview of the analysed variables. However, we do not aim to interpret the obtained results, merely draw attention to interesting patterns, that may be worth exploring in detail. Data used here are available upon request for further analyses.

Abstract Ornithological studies often rely on large temporal scale ringing datasets as source of information. However, basic descriptive statistics of collected data are rarely provided. In order to fill this gap, here we present the second item of a series of exploratory analyses of migration timing and body size measurements of the most frequent Passerine species at a ringing station located in Central Hungary (1984–2015). First, we give a concise description of foreign ring recoveries of the Dunnock in relation to Hungary. We then shift focus to data of 11,617 individuals deriving from the ringing station, where birds have been trapped, handled and ringed with standardized methodology since 1984. Timing is described through annual and daily capture and recapture frequencies and their descriptive statistics. We show annual mean arrival dates within the study period and we present the cumulative distribution of first captures with stopover durations. We present the distributions of wing, third primary, tail length and body mass, and the annual means of these variables. Furthermore, we show the distribution of individual fat and muscle scores, and the distribution of body mass within each fat score category. We distinguish migration periods (spring and autumn), and age groups (i.e. juveniles and adults). Our aim is to provide a comprehensive overview of the analysed variables. However, we do not aim to interpret the obtained results, merely draw attention to interesting patterns, that may be worth exploring in detail. Data used here are available upon request for further analyses.