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, Łódź, 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.

Sex allocation theory predicts equal offspring sex ratio when costs/benefits of producing each sex are comparable. However, when costs of rearing or fitness values of sexes vary, skewed offspring sex ratio toward the one sex may be beneficial. In this study we analysed seasonal secondary sex ratio (proportion of males) in broods of the Common Kingfisher Alcedo atthis, the socially monogamous, three- to four-brooded (per season) species with biparental care in which adult females are slightly larger than males. Fieldwork was carried out in the Danube river system from Bratislava to Gabčíkovo (SW Slovakia) during 2014–2018. In total, 959 nestlings from 149 broods of 78 breeding pairs were sexed, amongst which 483 were males and 476 were females. We considered the following assumptions: 1) no seasonal shift in sex ratio, as studied population occupies habitats rich in food; 2) female biased broods early in the season, as females' rapid maturation enables them to breed in the season they have been born; 3) male biased broods early in the season as several young males have been documented to be nest helpers. However, only a few such cases were observed, so it should be treated with caution. The sex ratio of individual broods ranged from 0 (all female) to 1 (all male), but the mean nestling sex ratio did not deviate from parity. We found no effect of year, brood size, or laying date. Thus, our results agree with outcomes of other avian studies where balanced seasonal sex ratio has been found.

Knowledge of the behaviour and survival of translocated individuals is vital for successful management of conservation programmes aimed at restoring species to their former distribution range. We examined movements and survival of 10 captive-bred Saker Falcons Falco cherrug fitted with satellite-received transmitters, which were released by wild-hacking in Bulgaria in 2012–2014. Chicks were parent-reared in captivity and transferred to hack cages when 25–35 days old in groups of 3–4 nestlings, where they were fed without direct human contact. After leaving the hack cages at 43–51 days old, fledglings were retained in the vicinity by food provisioning at the hack cage. Birds tracked by satellite remained in the vicinity of the hack cage for an average of 28 days (range 5–49 days) and post-dispersal survival was positively associated with the length of time spent in the hack vicinity. We found no significant difference in tracking period, as a proxy of survival, for translocated and wild-fledged Saker Falcons in Europe. The cause of transmission cessation was known for five birds; three were electrocuted by power distribution lines, one died after becoming trapped in a building and another was caught by falcon trappers in North Africa. Captive-bred birds exhibited similar movement and settlement behaviour as their wild congeners: dispersing at varied headings, establishing post-dispersal temporary settlement areas and migrating to discrete wintering ranges. Birds surviving to at least their second year showed some degree of natal philopatry, establishing summer ranges 45–160 km from their hack sites. Provisioning at feeding stations around the hack in 2015 and 2016 improved retention in the hack area to an average of 38 and 43 days, and apparent survival during the first 40-days after fledging was 97.7 and 98.9% respectively. A pair of Saker Falcons that bred in Bulgaria in 2018 and 2019 was from a trial cohort hacked in 2015, indicating that translocation of captive-bred birds can potentially be used to restore the species to this part of its former breeding distribution range.

Grassland fire suppression causes numerous ecological changes including increases in woody vegetation, reduced biodiversity, and population declines of grassland species. Elimination of vegetation structure created and maintained by fire is a major driver of these changes. In this study, we documented a seldom-described nesting preference in Brewer's Blackbirds Euphagus cyanocephalus through the discovery of 56 nests in recently burned (0 and 1 years-since-fire) mixed-grass prairie. After locating nests via systematic rope dragging, we monitored them to characterize fates and then measured vegetation characteristics at and near nests to determine how vegetation structure influences nest survival. Most Brewer's Blackbird nests were located in patches burned within 1.5 years of the nesting attempt, though such patches made up 21% of the landscape. Nests were located on the ground and consisted of fine grasses lined with animal hair. Site selection analysis showed that Brewer's Blackbirds were 38 and 34 times more likely to nest in 0 and 1 year-since-fire patches than unburned patches, respectively. Nest survival analysis indicated a daily survival rate of 0.96 (0.32 overall survival). Lower survival rates were associated with higher bare ground and litter cover at the microsite (5 m from nest) and nest site (at nest), respectively. These results demonstrate that Brewer's Blackbirds exploit fire-associated vegetation structure in tree-limited landscapes. This research suggests that restored grassland disturbance regimes extend broad benefits to non-obligate taxa, as well as reveals previously repressed fire-associated behaviors of wildlife.

Field margins are inherent elements of European agricultural landscapes, thought to be crucial for maintaining a high biodiversity level. The interactions between the structure of field margins and biota have been recognized, yet the understanding of the importance of various components of the margins and adjacent areas is still incomplete. The aim of our study was therefore to determine the relative importance of structural features of the margins and diversity of adjacent crops for birds breeding in field margins. The study was carried out in 70 field margins covered with semi-natural vegetation, situated in SW Poland. Both the number of species and bird density were most strongly positively related to the development of tree and shrub layers, while presence of ditches and percentage of reed cover (positive effects) had much less importance. Analyses conducted at the species level revealed the complexity of bird-habitat interactions resulting from various requirements of individual species. Overall, for 22 abundant species and for the threatened species, the development of the shrub layer turned out to be a particularly important feature of field margins positively associated with occurrence of e.g. Emberiza citrinella, Linaria cannabina and Streptopelia turtur. Other significant positive effects had the development of the tree layer (e.g. Turdus merula and Turdus philomelos), presence of ditch (e.g. Acrocephalus palustris, Sylvia communis), and number of gaps in woody vegetation (e.g. Lanius collurio). The diversity of adjacent crops had positive effects only to some threatened species (e.g. L. collurio and E. calandra). Abundances of common and threatened birds were not correlated, which reflects different habitat demands of these two groups. Because of diverse bird-habitat relationships, maintaining a variety of field margins (in particular the shrubby ones), should be accepted as a rule in biodiversity-oriented management of agricultural landscapes.

Changes in forest size and composition can affect Neotropical migratory songbirds breeding in Eastern North America, leading to population fluctuations and declines. In 2012–2014, we conducted point counts at locations previously surveyed in 1981–1983 and analysed Breeding Bird Atlas data from 1980–2013 to estimate long-term population trends of two declining ground-nesting warblers on the Eastern Shore of Maryland within the Atlantic Coastal Plain: the Ovenbird Seiurus aurocapilla and the Worm-eating Warbler Helmitheros vermivorum. We detected significant declines for Ovenbirds in both datasets, but we found conflicting data for Worm-eating Warblers. During 2012–2015, we investigated the effects of forest characteristics, such as vegetative composition and ground cover, on occupancy and nest success. Ovenbirds were found more where there were more and larger trees but were negatively affected by the proportion of pines, whereas Worm-eating Warblers were more abundant when there were higher numbers of trees and more pines. Nest success was not affected by vegetation other than the proportion of pine trees or leaf litter depth, both of which increased nest success. Worm-eating Warblers with more pine needles in their nests also had increased nest success. This study presents a nuanced view of how forest composition (proportion of pine trees) of the Atlantic Coastal Plain in Maryland influenced ground-nesting warblers differently, and suggests that effectively managing ground-nesting warblers in this area may differ from other regions of Eastern North America due to its unique vegetative composition, structure, and history.

In this study, we tested whether the Sharp-tailed Grouse Tympanuchus phasianellus experienced rapid demographic expansion and shifts in its distribution from the Last Glacial Maximum to the present and to the future. For this, we integrated two different approaches, phylogeography and ecological niche modeling, to understand the historical demography and the future of the Sharp-tailed Grouse under climate change scenarios. To this end, we re-analyzed two published mitochondrial DNA datasets to provide a comprehensive DNA characterization of populations across the range of this species. We used ecological niche models in tandem with landscape genetics to estimate the species current and historical geographic range, and to summarize effective connectivity among populations of the species at present. We found low genetic variation across the Sharp-tailed Grouse's distributions with almost no differentiation among subspecies. The haplotype network was consistent with star-shape topologies and showed no evident phylogeographic structure with the typical signature of recent demographic expansion. Taken together with the ecological niche modeling results, study outcomes supported the ‘expansion-contraction' model of Pleistocene biogeography. A unique result of this study was an apparently complete range shift of this species between the Last Glacial Maximum and the present, and a signature of cryptic refugium located in Alaskan territory in North America. The usual reason for lack of phylogeographic structure is broad dispersal, rapid expansion, and panmixia. However, in view of our novel geographic insights, a simpler explanation may be very recent establishment of the species’ range. The future predictions confirmed that the Sharp-tailed Grouse continues climate-driven range shifts in 2050 and 2070.

Food resource availability regulates population levels and reproductive success in several parrot species. Of the 59 threatened parrot species in the Neotropics, information on diet is available for only 34. Unsustainable forest management can eliminate trees with seeds and fruits that are key food resources for parrots. Tucuman Amazon Amazona tucumana is an endemic and threatened parrot species categorized as Vulnerable that occurs only in Andean montane forests of northwestern Argentina and southern Bolivia; i.e., the Southern Yungas. The diet of Tucuman Amazon, food availability, specialization, key food resources, and seasonal and spatial variation of food resources were determined. Feeding bouts of Tucuman Amazon were recorded from December 2007 to February 2009 in El Rey National Park. Availability of trees with seeds, fruits or flowers that could be used by Tucuman Amazon as food resources was assessed in phenology plots in cloud forest (high elevation humid forest) and transition forest (semideciduous forest located in the piedmont). Both forest types showed marked seasonality in availability of food resources for Tucuman Amazon. Sixty-six percent of this species feeding bouts were on seeds. Podocarpus parlatorei is the most widely used tree species by Tucuman Amazon in the cloud forest during the reproductive period and Acacia visco in the transition forest in the non-reproductive period. Podocarpus parlatorei could be critical for the development of Tucuman Amazon chicks, due to the high fat and oil content of its seeds and fruits. Tucuman Amazon used fewer food tree species during the non-reproductive than the reproductive period, showing a greater specialization of food resources (i.e., narrower niche breadth). To ensure the production of fruits of P. parlatorei and A. visco, sustainable forest management in the Southern Yungas should retain an adequate level of these key resources for Tucuman Amazon.

Food resources are linked to habitat characteristics and are one of the most important forces which constrain avian life histories. Availability of food affects avian body condition and strongly determines avian breeding performance. For many small passerines in the Northern Hemisphere, lepidopteran larvae (caterpillars) and arachnids are crucial dietary components during the rearing stage, but scarce information is available for Neotropical regions. In this study, we evaluated the relationship between the food delivery rates to the nestlings of caterpillars and arachnids and the tree-canopy cover and proportion of exotic trees of the nesting habitat of the insectivorous Masked Gnatcatcher Polioptila dumicola. In addition, as caterpillars and arachnids are high-quality prey-items for nestlings, we also evaluated whether differences in food delivery rates of these two prey-items were associated with nestlings' growth rates. We videotaped 23 nests in native forests of central-east Argentina during 2015–2018 breeding seasons. Both caterpillars and arachnids deliveries were positively associated with tree-canopy cover at the nest surroundings. Percentage of exotic tree-canopy cover in the nest surroundings was low (mean 8.18%), and was not associated with the frequency of food delivery. The proportion of arachnids delivered was positively associated with the asymptotic values of body mass and with the nestling tarsus maximum growth rate. Our results confirm that food resources are influenced by the tree-canopy cover in the nest surroundings, suggesting that less tree-covered patches of forests may contribute to a general decrease in the amount of food. We conclude that differences in nestling diet between habitats with different degree of tree cover contribute to explaining variance in the breeding performance of this species. Due to the alarming degree of alteration of these forests in recent decades, we highlight the importance of preserving forest portions with a high tree-cover that ensure better nestling growth in austral Masked Gnatcatcher's populations.

Successful reintroduction programmes are usually defined by an increase in size and extent of the new population after a given period of time. Among studies of birds, these population estimates are often focused on the monitoring of nesting attempts and productivity. For many raptors, however, this approach can overlook a large number of non-breeding adults and immature birds leading to underestimation of population size and reproductive potential. A more thorough approach is to generate assessments of total population size. In this study we used a line transect survey methodology and multiple covariate distance sampling to assess the change in population size of a reintroduced raptor species, Red Kite Milvus milvus, across a 2600 km² area of central southern England. Surveys were performed in spring and autumn between 2011 and 2016 in an area 45 km to the south of the initial English reintroduction project which started 25 years previously. Survey routes avoided using roads where possible to counter the potential attraction that such landscape features may have (e.g. increased food availability, perches etc.). The use of roads was unavoidable in some instances; however, we found no evidence of Red Kite attraction to these landscape features when comparing distances of observations from stretches along roads with 5000 randomly-generated locations. Distance of detection was influenced by bird activity (greatest when the bird was on the ground or interacting with other birds) and extent of woodland but not by time of day, seasonality or when comparing between years. During the five years, estimated population size doubled from approximately 490 to 1100 individuals; a density of one Red Kite per 2.5–3.5 km². This suggests an increase in the breeding population in the study area from c. 95 to 174 pairs. During the study, rate of population growth was not uniform; rapid growth was recorded in years two and three followed by a slowing over the last two years of the study. While an overall increase in population and availability of suitable nesting habitat across south-eastern England indicates that there is still potential for expansion of the Red Kite breeding population, other factors are potentially limiting this growth.

Incubation and rearing of nestlings are energetically demanding activities that can be affected by insulation conferred by the nest wall. Although thermal properties of nests are widely studied, no reports to date have dealt with the relative effects of the various structural parts of the nest wall. This experimental study investigated the effects of air movement, and for the first time, the effects of wall structure, on nest insulation for the Common Blackbird Turdus merula and Song Thrush Turdus philomelos of the Turdidae. Insulatory values, i.e. difference in cooling rate measured simultaneously inside and outside a nest, and internal cooling rates within the nest cup, were determined using temperature loggers under still-air and moving-air conditions. Moving-air increased insulatory values and internal cooling rates in both species. Insulatory values were positively correlated with the nest base thickness, but not nest side wall thickness. Removal of the outer nest wall and cup lining to reveal the internal mud cup of thrush nests reduced the insulatory value compared to the whole nest, the effect of which was exacerbated under moving-air conditions. These results may reflect that the nest wall confers huge insulatory advantages and especially so during periods of air movement. However, it is unclear whether this is related to the presence of particular nest materials that confer insulation, or to the amount of air trapped in the nest wall. Alternatively, the thermal conductivity of the materials lining the cup wall may be important.

Birds are expected to orient their nests non-randomly in order to avoid extreme thermal conditions that are known to affect their reproductive success. Considering the hypotheses that yearly mean temperature influences entrance orientation in birds, nests at higher latitudes are expected to face the equator in order to take advantage of warmer temperatures. Here we explore the relationship between latitude and nest entrance orientation in closed nests of Passeriformes in the southern Neotropics (Furnariidae, Rhinocryptidae, Troglodytidae, Tyrannidae), using both published and original data. We found a positive and significant correlation between mean entrance orientation and latitude, and report significantly non-random nest orientation at 62% of the locations with available samples. Overall, there is a trend for nests at lower latitudes to have north-northeasterly orientations, and for nests at higher latitudes to be oriented northwest. The reasons for the observed trends remain unclear, but likely involve the availability and intensity of solar radiation and its effect upon the nest microclimate.