The Influence of Biological Factors on Haematological Values in Wild Marsh Harrier (Circus aeruginosus) Nestlings

Marsh harrier (Circus aeruginosus) is a species with obligatory cainism, in which hatching asynchrony creates a pronounced size hierarchy in nestlings. The size-related competitive advantage of older nestlings means that they tend to dominate the younger ones, and brood reduction occurs in most nests. The aim of the study was to reference values and carry out a haematological examination in order to evaluate the physiological status and health of nestlings with respect to hatching order, brood size, and nest initiation date. To do so, we examined 19 nests with a total of 58 nestlings from a free-living population of this species located in fishpond complexes in the agricultural landscape of eastern Poland. Repeated blood samples (118 in all) were collected from nestlings. The following parameters were measured using fresh full blood: red blood cell count (RBC), haemoglobin level (Hb), white blood cell count (WBC), and plasma glucose level (Glu). The data were analysed using generalized linear mixed models and linear mixed models ((G)LMM). The study revealed that hatching order, but not brood size or nest initiation date, affected the physical condition of marsh harrier nestlings. Hb levels and RBC counts gradually decreased, whereas Glu levels and WBC counts increased from the first- to the last-hatched nestlings. This result points to the generally poorer condition of the youngest nestlings compared with their older siblings. The poor physiological condition of the youngest nestlings may consequently increase the likelihood of their perishing, and hence, of brood reduction.

Host traits and lifetime fitness costs of being parasitized in red-breasted mergansers

The addition of eggs to a nest by a conspecific is known for approximately 250 bird species. Understanding the evolution of conspecific brood parasitism (CBP) requires assessment of fitness consequences to the egg recipient (host). We addressed host traits and the effects of CBP on future reproduction (i.e., annual survival) and hatching success of hosts by following the nesting of 206 red-breasted mergansers ( Mergus serrator) for a colony in which an average of 41% of nests was parasitized annually. Each host was tracked for ≥2 seasons and up to seven seasons. The proportion of a host’s nesting attempts that was parasitized averaged 43% and varied considerably across individuals (range 0%–100%). Probability of parasitism, however, was not repeatable across a host’s nests. Rather, rates of CBP throughout a host’s lifetime increased with earlier dates of nest initiation. CBP had no effect on annual survival of a host. Hatching success throughout a host’s lifetime declined with a greater number of foreign eggs added to the individual’s nests. This study revealed that there may be measurable costs of CBP to lifetime reproductive success in red-breasted mergansers, although our observations suggest that costs to hosts are limited to the most heavily parasitized clutches.

Burrowing Owl (Athene cunicularia) nest phenology influenced by drought on nonbreeding grounds

Migratory birds are demonstrating changes in phenology linked to climate change. Understanding these changes requires connecting events that occur over the multiple regions occupied during their annual cycle. The Burrowing Owl (Athene cunicularia) is a species of concern in North America, with pronounced declines in regions of the Great Plains. Using a dataset that spanned 10 breeding sites from South Dakota to northern Mexico in various years during 1989–2017, we observed both advances and delays in nesting along with increasing variation in nest initiation dates. We examined the effects of a large-scale climate system (El Niño Southern Oscillation), drought, and local weather patterns throughout the annual cycle as potential predictors of early and late nesting. Moisture conditions during the winter and spring migratory period had the greatest influence on nest phenology. Years with more intense drought on winter and migratory grounds increased the probability of nests initiating late relative to early. Correspondingly, wet conditions were associated with an increased probability of early nest initiation. Drought likely has cascading ecological effects that negatively influence food abundance for Burrowing Owls, resulting in delays in the ability of individuals to meet energetic demands required for migration. How climate change will impact Burrowing Owl phenology is important considering a projected increase in the magnitude and frequency of drought and declining owl population trends.

Influence of Nesting Characteristics on Health of Wild Bee Communities

Nest site availability and quality are important for maintaining robust populations and communities of wild bees. However, for most species, nesting traits and nest site conditions are poorly known, limiting both our understanding of basic ecology for bee species and conservation efforts. Additionally, many of the threats commonly associated with reducing bee populations have effects that can extend into nests but are largely unstudied. In general, threats such as habitat disturbances and climate change likely affect nest site availability and nest site conditions, which in turn affect nest initiation, growth, development, and overwintering success of bees. To facilitate a better understanding of how these and other threats may affect nesting bees, in this review, I quantify key nesting traits and environmental conditions and then consider how these traits may intersect with observed and anticipated changes in nesting conditions experienced by wild bees. These data suggest that the effects of common threats to bees through nesting may strongly influence their survival and persistence but are vastly understudied. Increasing research into nesting biology and incorporating nesting information into conservation efforts may help improve conservation of this declining but critical group.

The environmental predictors of spatio-temporal variation in the breeding phenology of a passerine bird

Establishing the cues or constraints that influence avian timing of breeding is the key to accurate prediction of future phenology. This study aims to identify the aspects of the environment that predict the timing of two measures of breeding phenology (nest initiation and egg laying date) in an insectivorous woodland passerine, the blue tit ( Cyanistes caeruleus ). We analyse data collected from a 220 km, 40-site transect over 3 years and consider spring temperatures, tree leafing phenology, invertebrate availability and photoperiod as predictors of breeding phenology. We find that mean night-time temperature in early spring is the strongest predictor of both nest initiation and lay date and suggest this finding is most consistent with temperature acting as a constraint on breeding activity. Birch budburst phenology significantly predicts lay date additionally to temperature, either as a direct cue or indirectly via a correlated variable. We use cross-validation to show that our model accurately predicts lay date in two further years and find that similar variables predict lay date well across the UK national nest record scheme. This work refines our understanding of the principal factors influencing the timing of tit reproductive phenology and suggests that temperature may have both a direct and indirect effect.

Post-release breeding of translocated sharp-tailed grouse and an absence of artificial insemination effects

Context Translocation has become a widely used method to restore wildlife populations following extirpation. For some species, such as lekking grouse, which breed at traditional mating grounds, reproduction is linked to culturally established geographic locations. Cultural centres are lost upon extirpation, making restoration into otherwise rehabilitated habitats especially challenging. The process by which species with culturally dependent reproduction sometimes become re-established is poorly understood and merits investigation to improve conservation strategies. Historically, population restoration of North American lekking grouse (Tympanuchus spp. and Centrocercus spp.) via translocation has yielded poor results, in part because translocation sites lack leks, culturally determined breeding locations for which breeding adults form a high degree of philopatry. Columbian sharp-tailed grouse (Tympanuchus phasianellus columbianus; CSTG) occurs in <10% of its historic range, but the existence of rehabilitated historic habitat provides for the potential of population restoration via translocation. Aims We reintroduced CSTG to vacant habitat in north-central Nevada, USA, from 2013 to 2017, with concordant goals of promoting females to nest and males to lek. We tested the utility of performing artificial insemination (AI) on females before translocation and we conducted paternity analyses to understand male reproduction. Methods We monitored females for the effects of AI on nest initiation, nest survival and egg fertility. We used post-hatch extra-embryonic membranes and other tissues to evaluate paternity of chicks produced at the restoration site. Key results Artificial insemination had no effect on female survival or nest initiation, and did not fertilise any eggs within nine sampled clutches (n=102 eggs). Most paternity was attributable to male residents that had survived for ≥1 year at the restoration site before the arrival of translocated females. Conclusions Artificial insemination neither aided nor harmed female reproduction. A small number of translocated, resident adult males sired reproduction following female release. Implications The presence of resident males at restoration sites may be more likely to result in post-translocation reproduction than is pre-translocation AI. Restoring CSTG to vacant habitat should focus on translocating females into suitable nesting habitat while simultaneously ensuring that reproductively capable males are available within or adjacent to the nesting habitat.

Effects of neonicotinoid insecticide exposure and monofloral diet on nest-founding bumblebee queens

Bumblebees are among the world's most important groups of pollinating insects in natural and agricultural ecosystems. Each spring, queen bumblebees emerge from overwintering and initiate new nests, which ultimately give rise to workers and new reproductives later in the season. Nest initiation and survival are thus key drivers of both bumblebee pollination services and population dynamics. We performed the first laboratory experiment with the model bumblebee species Bombus impatiens that explores how early nesting success is impacted by the effects of temporary or more sustained exposure to sublethal levels of a neonicotinoid-type insecticide (imidacloprid at 5 ppb in nectar) and by reliance on a monofloral pollen diet, two factors that have been previously implicated in bumblebee decline. We found that queens exhibited increased mortality and dramatically reduced activity levels when exposed to imidacloprid, as well as delayed nest initiation and lower brood numbers in the nest, but partially recovered from these effects when they only received early, temporary exposure. The effects of pollen diet on individual queen- and colony-level responses were overshadowed by effects of the insecticide, although a monofloral pollen diet alone was sufficient to negatively impact brood production. These findings speak to the sensitivity of queen bumblebees during the nest initiation phase of the colony cycle, with implications for how queens and their young nests are uniquely impacted by exposure to threats such as pesticide exposure and foraging habitat unsuitability.