Avian Population Dynamics Research Articles

Environmental conditions influence host-parasite interactions and host fitness in a migratory passerine.

The study of host-parasite co-evolution is a central topic in evolutionary ecology. However, research is still fragmented and the extent to which parasites influence host life history is debated. One reason for this incomplete picture is the frequent omission of environmental conditions in studies analyzing host-parasite dynamics, which may influence the exposure to or effects of parasitism. To contribute to elucidating the largely unresolved question of how environmental conditions are related to the prevalence and intensity of infestation and their impact on hosts, we took advantage of 25 years of monitoring of a breeding population of pied flycatchers, Ficedula hypoleuca, in a Mediterranean area of central Spain. We investigated the influence of temperature and precipitation during the nestling stage at a local scale on the intensity of blowfly (Protocalliphora azurea) parasitism during the nestling stage. In addition, we explored the mediating effect of extrinsic and intrinsic factors and blowfly parasitism on breeding success (production of fledglings) and offspring quality (nestling mass on day 13). The prevalence and intensity of blowfly parasitism were associated with different intrinsic (host breeding date, brood size) and extrinsic (breeding habitat, mean temperature) factors. Specifically, higher average temperatures during the nestling phase were associated with lower intensities of parasitism, which may be explained by changes in blowflies' activity or larval developmental success. In contrast, no relationship was found between the prevalence of parasitism and any of the environmental variables evaluated. Hosts that experienced high parasitism intensities in their broods produced more fledglings as temperature increased, suggesting that physiological responses to severe parasitism during nestling development might be enhanced in warmer conditions. The weight of fledglings was, however, unrelated to the interactive effect of parasitism intensity and environmental conditions. Overall, our results highlight the temperature dependence of parasite-host interactions and the importance of considering multiple fitness indicators and climate-mediated effects to understand their complex implications for avian fitness and population dynamics.

First sighting record of Western Reef-Heron Egretta gularis (Bosc, 1792) (Aves: Pelecaniformes: Ardeidae) from Jammu & Kashmir, India

We report the first documented sighting of a Western Reef-Heron (Egretta gularis) in Jammu & Kashmir, India. The Western Reef-Heron, a medium-sized heron, was previously considered a subspecies of the Little Egret. The sighting occurred on June 18, 2023, at Wular Lake, expanding the avifaunal diversity of the region. The heron remained in the vicinity of the lake for several days, allowing for detailed observation and study. This particular bird belonged to the dark morph category, displaying distinct characteristics. The Western Reef-Heron is primarily found in coastal regions across Africa but has also been observed as a vagrant species in southern Europe. The sighting at Wular Lake contributes to our understanding of the avian population and ecological dynamics in the region. Wular Lake, situated in the Kashmir valley, is one of Asia's largest wetlands and plays a crucial role in water flow regulation, agriculture, and fisheries. It has recently become a hotspot for diverse bird species, including several notable first-time sightings in Jammu & Kashmir

Elevational differences in migration phenology of Lazuli Buntings do not support selection-based hypotheses for protandry

Abstract Documenting and understanding sex-specific variation in migratory phenology is important for predicting avian population dynamics. In spring, males often arrive on the breeding grounds before females (protandry), though whether these patterns result from fitness benefits vs. sex-specific constraints on arrival timing remains poorly understood. Sex-specific variation in the timing of fall migration is less well-documented than in spring, in part because documenting fall departures is often limited by cryptic behaviors, lower vocalization rates, and shifting territory boundaries during this time of year. We used 2 years of high-resolution encounter data from radio-frequency identification (RFID)-equipped bird feeders to monitor the daily presence of male and female Lazuli Buntings (Passerina amoena) throughout the breeding season at a high and a low-elevation site in Cache County, Utah, USA. These encounter data were used to estimate daily arrival and departure probabilities and to investigate possible differences in migration timing in relation to sex and elevation. At low elevation, male arrival (n = 15) preceded female arrival (n = 16) by ~1 week, consistent with previous research that has documented protandry in other migratory songbirds. At high elevation, however, no significant differences were found between male (n = 19) and female arrival (n = 6). In fall, we found little difference in departure dates between elevation or sex, or between years. Our observations are most consistent with constraint-based hypotheses explaining protandry, possibly relating to sex-specific constraints operating during the nonbreeding period. We additionally emphasize the need for quantifying uncertainty in phenological estimates and importance of addressing potential differences across demographic groups.

Factors affecting apparent survival and resighting probability of wintering mallards Anas platyrhynchos

Survival of adults is a key demographic parameter affecting avian population dynamics. In urban areas, e.g., city parks, birds stay in winter in large numbers where they have access to a multitude of food sources due to human activities, which is one of the key factors that attract birds into the cities. Our study estimates apparent survival of mallard ducks Anas platyrhynchos between non-breeding seasons in a small town in the coldest region in north-eastern Poland between 2005 and 2017. We found lower survival estimates for females (juveniles: 0.54; adults: 0.59) than males (juveniles: 0.76; adults: 0.72) and probabilities of resighting individuals in the next non-breeding season were higher if the bird was resighted in the study area during the prior breeding period. Thus, we conclude that sedentary mallards from the local urban population have relatively high survival, which may be explained by lower pressure from raptors, lack of hunting and higher winter temperatures in the urban site. Additionally, winter temperature was negatively related to resighting probability in the next non-breeding season. Resighting probability was time-dependent with a bimodal pattern with maximal estimates of 0.48 in 2007/2008 and 0.98 in 2013/2014, 0.98 in 2014/2015, 1.00 in 2015/2016. These results are most likely related to volunteers’ activity that increased due to organized official competition with special awards during those seasons. Considering the fact that the type of ring (metal or plastic coloured) significantly influenced the probabilities of resighting of individuals, it is recommended that apparent survival studies on birds be conducted using colour rings. Moreover, we encourage to collect more capture-mark-recapture data to enable accurate estimations of duck survival, which not the least is a prerequisite for successful management and conservation efforts.

Effects of nest-box environment on fledgling success rate and pathogen load.

Nest boxes have been used for many decades as tools for conservation and to study avian population dynamics. Plastic is increasingly used as a material for nest boxes, but no studies have investigated effects of this different material. Two consecutive studies were conducted to investigate effects of nest-box environment on nidicolous parasites, bacteria and fungi, as well as nest success, in blue tits Cyanistes caeruleus and great tits Parus major. The first compared microclimate and parasite and pathogen load in plastic and wooden nest boxes. The second tested the nest protection hypothesis – that birds naturally incorporate aromatic herbs into nests to decrease nest parasites and pathogens – by comparing parasite and pathogen load in plastic nest boxes to which aromatic or non-aromatic plant material was added. No significant difference in nest-box temperature or relative humidity was found between plastic and wooden boxes. Wooden boxes, however, contained 30-fold higher numbers of fleas and a higher total bacterial load on chicks. Fledging success for blue tit broods was significantly higher in wooden boxes. Parasites and bacteria did not decrease by the inclusion of aromatic herbs. The results increase the evidence base for nest-box design in support of plastic, which can provide an appropriate alternative nest-box material to wood, with apparently no difference in microclimate and no increase in the load of measured parasites and pathogens.

Diverse demographic factors influence apparent juvenile survival in a migratory songbird

AbstractTo better understand the dynamics of avian populations and their role in population trends, we require an in‐depth understanding of the factors influencing the survival of adults and juveniles. However, assessing survival in juveniles is often challenging, especially in small, migratory species where individuals typically disperse from the study area and are not available for recapture in subsequent years. Bobolinks (Dolichonyx oryzivorus) are a long‐distance migrant that exhibits natal philopatry in at least one population, allowing for more comprehensive juvenile survival analyses than in many other long‐distance avian migrants. Using a 17‐yr dataset from two sites representing a Vermont population of Bobolinks, we used Program MARK to assess factors influencing apparent juvenile survival, including factors related to nesting timing, nest attempt number, the philopatric behaviors of relatives, body mass, brood size, and agricultural management scheme. Our top models indicated that nest attempt number and whether or not a nest mate also survived and returned to breed locally were important factors explaining variation in apparent survival in juvenile Bobolinks. Specifically, juveniles from first nest attempts that fledged earlier in the season, with siblings that did not survive and return to breed locally, showed higher apparent survival. Factors such as site and the philopatric behavior of females associated with nests also appeared in top‐ranking models, while factors such as body mass and brood size did not. These results indicate the importance of providing high‐quality breeding habitat to birds early in the season when juvenile survival is greatest and indicate that individuals may be utilizing inbreeding avoidance strategies. These results provide new insight into the ecological and agricultural management factors influencing survival in migratory species that use managed habitats and underscore the importance of integrating juvenile survival data into current management schemes to better support this and other declining species.

Differential effects of policy-based management on obligate and facultative grassland birds

Policy-driven conservation on private lands, such as the U.S. Farm Bill’s Conservation Reserve Program (CRP), provides crucial habitat for consistently declining populations of grassland birds. In 2004, new CRP enrollments were required to be managed to floristically diversify old grass-dominated fields and provide early-successional habitat. Obligate and facultative grassland birds of varying conservation importance, along with the entire avian community, has received limited research attention within this applied management context. Moreover, multiple parameters (e.g. nest survival and adult density) – opposed to single parameter studies – need to be investigated simultaneously to better understand drivers of avian population dynamics associated with management. Using a combination of graphical and model selection approaches we addressed these gaps focusing on four main questions: 1) How does abundance and richness of various grassland bird community designations respond to broad (e.g. grass type) and specific (control, disking, herbicidal spray, and spray/interseeding) management treatments?; 2) How do grassland birds of conservation concern and economic importance collectively respond to management?; 3) Are various response parameters, including nesting parameters, consistent or decoupled across facultative and obligate species?; and 4) Is there a best management treatment to recommend? Overall, compared to non-native grass (smooth brome [Bromus inermis]) dominated fields, native fields had a greater number of avian species and number of individuals with higher and lower cumulative management, respectively. Facultative grassland species were mostly driving this trend and likely utilizing native fields that tended to have more vertical vegetation structure and forb diversity compared to brome fields. Grassland obligates with higher Conservation Values, such as bobolinks (Dolichonyx oryzivorus), however, were most abundant and species-rich on unmanaged brome fields compared to native fields. Response parameter decoupling was not readily apparent from our comprehensive modeling analysis of both adult survey and nesting data; however, nest survival was generally higher on native fields for eastern meadowlarks (Sturnella magna), an obligate, yet adult densities for meadowlarks were greater on unmanaged brome fields. Overall, pinpointing a specific mid-contract management practice for CRP that has benefits for all grassland birds remains challenging due to species-specific habitat requirements. However, it appeared the moderate effects of light strip-disking on vegetation may present a good management option for landowners because this treatment may be beneficial across multiple species of grassland birds and would also limit the impact of management to obligates utilizing unmanaged brome fields while also improving the avian Conservation Value of native fields.

Behavioral strategies during incubation influence nest and female survival of Wild Turkeys.

Females must balance physiological and behavioral demands of producing offspring with associated expenditures, such as resource acquisition and predator avoidance. Nest success is an important parameter underlying avian population dynamics. Galliforms are particularly susceptible to low nest success due to exposure of ground nests to multiple predator guilds, lengthy incubation periods, and substantive reliance on crypsis for survival. Hence, it is plausible that nesting individuals prioritize productivity and survival differently, resulting in a gradient of reproductive strategies. Fine‐scale movement patterns during incubation are not well documented in ground‐nesting birds, and the influence of reproductive movements on survival is largely unknown. Using GPS data collected from female wild turkeys (n = 278) across the southeastern United States, we evaluated the influence of incubation recess behaviors on trade‐offs between nest and female survival. We quantified daily recess behaviors including recess duration, recess frequency, total distance traveled, and incubation range size for each nest attempt as well as covariates for nest concealment, nest attempt, and nest age. Of 374 nests, 91 (24%) hatched and 39 (14%) females were depredated during incubation. Average nest survival during the incubation period was 0.19, whereas average female survival was 0.78. On average, females took 1.6 daily unique recesses (SD = 1.2), spent 2.1 hr off the nest each day (SD = 1.8), and traveled 357.6 m during recesses (SD = 396.6). Average nest concealment was 92.5 cm (SD = 47). We found that females who took longer recess bouts had higher individual survival, but had increased nest loss. Females who recessed more frequently had lower individual survival. Our findings suggest behavioral decisions made during incubation represent life‐history trade‐offs between predation risk and reproductive success on an unpredictable landscape.

Comparing community birdwatching and professional bird monitoring with implications for avian diversity research: a case study of Suzhou, China

BackgroundIn the past decades, birdwatching as a hobby developed rapidly and produced ample scientific records that have aided conservation efforts. Therefore, it is increasingly attractive to promote avian research by providing data from birdwatching.MethodsWe compared records from 16 years of community birdwatching and a 1-year formalized bird monitoring in Suzhou, China to study the similarities and differences between the two monitoring methods.ResultsWe showed that within the 325 bird species recorded by the two methods, an annual average of 108 species were documented by community science and 223 bird species were recorded by 1-year formalized monitoring. Measured by the number of bird species recorded per survey trip, the bird monitoring activity of community birdwatchers was significantly lower. Furthermore, the monitoring intensity of community birdwatching measured as the average survey trips per site each survey year was also lower than that of formalized bird monitoring. In addition, community birdwatchers preferred urban landscapes to rural areas.ConclusionsCommunity birdwatching could record the majority of local birds and complements the professional surveys in avian research. Well designed and coordinated community science can be used to expand the knowledge about avian distribution and population dynamics. These findings are critical for the development of conservation science with regard to community involvement.

The importance of functional responses among competing predators for avian nesting success

AbstractThe relationship between the rate of predation and prey abundance is an important component of predator–prey dynamics. However, functional responses are less straightforward when multiple predators compete for shared prey. Interactions among competing predators can reduce or enhance effects of predation on prey populations. Because many avian populations experience high rates of nest predation, understanding the role of specific predators on nest mortality will lead to more informed conservation and management strategies which attempt to increase productivity by removing certain predators or managing habitat to limit their impact.Our goal was to evaluate effects of specific predators and the influence of nest abundance on nest mortality.We monitored snowy ploverCharadrius nivosusnests across 7 years at two study areas in Utah, USA, with remote cameras. We modelled predator‐specific hazard rates for nest mortality in a Bayesian framework to assess relationships between competing predators and the role of nest abundance on predator‐specific hazard rates.We found that hazard rates for nest mortality by gullsLarusspp. decreased with increasing nest abundance, whereas nest mortality by foxesVulpesspp. and ravensCorvus coraxinitially increased, indicating that dietary switching may occur when nests become more abundant. Nest mortalities of specific predators were often not independent and ranged between compensatory (e.g. mammalian mesopredators) and superadditive (e.g. avian predators) across the breeding season.The non‐independence between nest mortalities suggests that reductions in some predators may not translate to additive increases in overall nest success. Analyses of cause‐specific mortality are rarely applied to avian nests, but examination of interacting impacts among competing predators on nest survival may provide insight into specific drivers of avian population dynamics.A freePlain Language Summarycan be found within the Supporting Information of this article.

Does acoustically simulated predation risk affect settlement and reproduction of a migratory passerine?

AbstractNest predation is one of the most important drivers of avian life history evolution and population dynamics. Increasing evidence suggests that birds are able to assess nest predation risk and avoid settling in high‐risk areas to increase their reproductive performance. However, the cues used for settlement decisions are poorly known in most species. Population sizes of the migratory wood warblerPhylloscopus sibilatrixare characterized by strong annual fluctuations, which are negatively correlated with the number of forest rodents. Wood warblers might avoid rodent‐rich areas to reduce predation risk arising either from rodents, from rodent‐hunting predators attracted to such areas or from predators not linked to rodents. To evaluate these hypotheses, we conducted a large‐scale field experiment to test whether wood warblers avoided settling in plots with high predation risk simulated by broadcasting vocalizations of rodents or predators. Moreover, we tested whether reproductive performance varied in relation to simulated predation risk. Settlement patterns did not differ between plots with rodent, predator and noise control treatments. Likewise, measures of reproductive performance did not seem to differ across treatments. Thus, the broadcasted vocalizations of rodents and predators did not seem to be perceived as threat by wood warblers. Alternatively, the species might use other cues than those presented here, either other acoustic cues, visual and/or olfactory cues or a combination of cue types during settlement. Further experimental investigations to pin point cues and senses relevant for settlement decisions in wood warblers and birds in general are needed to better understand their life history and population dynamics.

Prevalence of BFDV in wild breeding Platycercus elegans

Pathogens can have a profound impact on the population dynamics of avian populations. Beak and feather disease virus (BFDV) is considered one of the few pathogens capable of causing extinction, because it predominantly infects the highly threatened order Psittaciformes, the signs of disease are severe, and mortality can be extremely high. Little is known about BFDV in wild populations, particularly its distribution among wild breeding birds. We investigated patterns of BFDV infection in family groups across three different subspecies of a common southeast Australian parrot (Platycercus elegans). We predicted that due to the high degree of contact, shared environment and high relatedness within family units, the prevalence of infection would be uniform. However, we found more non-infected breeding pairs than expected if there was random mating, whilst cases where both pair members were infected were observed less often than expected under random mating. When one pair member was infected, it was sex-biased, with males rarely infected. We found that parental infection status did not explain nestling infection status, suggesting that other infection routes (e.g. from the hollow or nest material) are likely. Future work is needed to assess transmission and behavioural mechanisms that explain patterns of infection among breeding birds.

Integrated tool for microsatellite isolation and validation from the reference genome and their application in the study of breeding turnover in an endangered avian population.

Accurate individual identification is required to estimate survival rates in avian populations. For endangered species, non-invasive methods of obtaining individual identification, such as using molted feathers as a source of DNA for microsatellite markers, are preferred because of less disturbance, easy sample preparation and high efficiency. With the availability of many avian genomes, a few pipelines isolating genome-wide microsatellites have been published, but it is still a challenge to isolate microsatellites from the reference genome efficiently. Here, we have developed an integrated tool comprising a bioinformatic pipeline and experimental procedures for microsatellite isolation and validation based on the reference genome. We have identified over 95 000 microsatellite loci and established a system comprising 10 highly polymorphic markers (PIC value: 0.49-0.93, mean: 0.79) for an endangered species, saker falcon (Falco cherrug). These markers (except 1) were successfully amplified in 126 molted feathers, exhibiting high amplification success rates (83.9-99.7%), high quality index (0.90-0.97) and low allelic dropout rates (1-9.5%). To further assess the efficiency of this marker system in a population study, we identified individual sakers using these molted feathers (adult) and 146 plucked feathers (offspring). The use of parent and offspring samples enabled us to infer the genotype of missing samples (N = 28), and all adult genotypes were used to ascertain that breeding turnover is a useful proxy for survival estimation in sakers. Our study presents a cost-effective tool for microsatellite isolation based on publicly available reference genomes and demonstrates the power of this tool in estimating key parameters of avian population dynamics.

Bayesian spatiotemporal dynamic models for regional dynamics of avian populations

The spatiotemporal dynamics of multiple animal populations may exhibit the hierarchical dynamic patterns including regional common trends or spatial synchrony and local variability. Environmental drivers such as climatic variability, operating on large spatial scales, have been proposed to be a driver of the spatial synchrony of avian and mammalian populations (i.e., the Moran effect). On the other hand, demographic responses to heterogeneous, local environments may result in substantial local population variability (i.e., variance across multiple populations). This study used the Bayesian hierarchical spatiotemporal dynamic model to determine the spatiotemporal dynamic patterns of 27 eastern wild turkey (Meleagris gallopavo silvestris) populations scattered across Mississippi, USA, from 1994 to 2005. The regional effects of seasonal climate and relative amount of forest in habitats were also evaluated to test the Moran effect. Twenty seven wild turkey populations had a spatial synchrony with the strength and spatial scale similar to those of other avian populations in North America. Warming spring or spring-autumn climate appeared to reduce wild turkey relative abundance; however, winter climate did not influence the dynamics of wild turkey populations in Mississippi. Average proportion of forest affected the average relative abundance of wild turkeys in a nonlinear manner, with its positive effects switching to a lessened constant effect beyond the threshold of 60% forest cover. However, regional climatic variability was unlikely to synchronize wild turkey populations in Mississippi. This study proposed a hypothesis concerning regional habitat quality degradation, which may cause regional population declines and synchronize the dynamics of animal populations.

Spatial and temporal drivers of avian population dynamics across the annual cycle.

Untangling the spatial and temporal processes that influence population dynamics of migratory species is challenging, because changes in abundance are shaped by variation in vital rates across heterogeneous habitats and throughout the annual cycle. We developed a full-annual-cycle, integrated, population model and used demographic data collected between 2011 and 2014 in southern Indiana and Belize to estimate stage-specific vital rates of a declining migratory songbird, the Wood Thrush (Hylocichla mustelina). Our primary objective was to understand how spatial and temporal variation in demography contributes to local and regional population growth. Our full-annual-cycle model allowed us to estimate (1) age-specific, seasonal survival probabilities, including latent survival during both spring and autumn migration, and (2) how the relative contribution of vital rates to population growth differed among habitats. Wood Thrushes in our study populations experienced the lowest apparent survival rates during migration and apparent survival was lower during spring migration than during fall migration. Both mortality and high dispersal likely contributed to low apparent survival during spring migration. Population growth in high-quality habitat was most sensitive to variation in fecundity and apparent survival of juveniles during spring migration, whereas population growth in low-quality sites was most sensitive to adult apparent breeding-season survival. These results elucidate how full-annual-cycle vital rates, particularly apparent survival during migration, interact with spatial variation in habitat quality to influence population dynamics in migratory species.

Salton Sea days of future past: Modeling impacts of alternative water transfer scenarios on fish and bird population dynamics

The Colorado River Quantification Settlement Agreement (QSA) of 2003 gives urgency for studying the environmental consequences of the cessation of mitigation water transfers to the Salton Sea. The Salton Sea Stochastic Simulation Model (S4M) is a spatially-driven, stochastic, simulation model representing water flow, i.e., water volume and quantity of Total Dissolved Solids and Phosphorus, in the Lower Colorado River Basin, Mexicali Valley, and the Salton Sea Basin. The S4M is formulated as a compartment model based on difference equations with a daily time step using STELLA® v8.0. The model was developed, evaluated, and applied to simulate the potential effects on the population dynamics, i.e., natality, mortality, emigration, and immigration, of selected fish and avian species at the Salton Sea under two different scenarios: 1) QSA water transfers to Sea end after 2017 and 2) QSA water transfers continue at 2017 levels. Oneway ANOVAs were performed for the water quantity, water quality, and selected variables involving the fish and bird population dynamics under the two water transfer scenarios. Results indicate that if cessation of the QSA water transfers after 2017 occurs, then fish and bird populations will be significantly (P<0.05) and negatively impacted by year 2024, compared to continuing the QSA water transfers. Further, if no restoration action is taken in stabilizing the Sea elevation and reducing salinity but continuing QSA water transfers (at 2017 levels), i.e., scenario 2; results indicate that Salton Sea avian and fish population dynamics will be negatively impacted, although somewhat delayed.

The influence of climatic variation and density on the survival of an insular passerine Zosterops lateralis.

Understanding the influence of environmental factors on population dynamics is fundamental to many areas in biology. Survival is a key factor of population biology, as it is thought to be the predominant driver of growth in long-lived passerines, which can be influenced by both biotic and abiotic environmental conditions. We used mark-recapture methods and generalized linear mixed models to test the influence of density and climatic variation, measured at a regional and local scale (Southern Oscillation Index [SOI] and rainfall, respectively), on seasonal variation in survival rates of an insular population of Silvereyes (Zosterops lateralis chlorocephalus), during a 15-year study period, off the east coast of Australia. We found overall high survival rates for adults and juveniles (81% and 59%, respectively). Local scale climate (i.e. rainfall) and density were the principal environmental factors influencing their survival, both with a negative relationship. A significant interactive effect of density and rainfall influenced survival as they both increased. However, survival remained low when density was at it highest, independent of the amount of rainfall. Nestling survival was negatively influenced by rainfall and density, positively by SOI, and chicks that hatched later in the breeding season had higher survival rates. The regional scale climate variable (i.e. SOI) did not explain survival rates as strongly as rainfall in any age class. Our results contribute to the understanding of insular avian population dynamics and the differential effects of environmental factors across age classes. Climatic predictions expect El Niño events to increase, meaning dryer conditions in eastern Australia, potentially increasing Silvereye survival across age classes. However, the long-term effect of lower rainfall on food availability is unknown; consequently, the outcome of lower rainfall on Silvereye survival rates is uncertain.

A recipe for postfledging survival in great tits Parus major: be large and be early (but not too much).

Survival of juveniles during the postfledging period can be markedly low, which may have major consequences on avian population dynamics. Knowing which factors operating during the nesting phase affect postfledging survival is crucial to understand avian breeding strategies. We aimed to obtain a robust set of predictors of postfledging local survival using the great tit (Parus major) as a model species. We used mark–recapture models to analyze the effect of hatching date, temperatures experienced during the nestling period, fledging size and body mass on first‐year postfledging survival probability of great tit juveniles. We used data from 5192 nestlings of first clutches ringed between 1993 and 2010. Mean first‐year postfledging survival probability was 15.2%, and it was lower for smaller individuals, as well as for those born in either very early or late broods. Our results stress the importance of choosing an optimum hatching period, and raising large chicks to increase first‐year local survival probability in the studied population.

Predation and reduced grazing interact to reduce recruitment and population growth in Black Brant

ABSTRACT Dynamics of avian populations may be governed by a complex interaction between immediate effects of predation and longer-term trophic feedbacks between individuals and their foods. We used a long-term study of uniquely marked Black Brant geese (Branta bernicla nigricans) to estimate recruitment into the breeding population. We related recruitment to nest success, which directly affects recruitment 2 to 3 years later. We also assessed similarly time-lagged relationships between recruitment and number of nests in the colony, a measure of local density, and pre-fledging and first-year survival, the latter of which is strongly influenced by growth conditions and food availability for young of the year. We assessed relationships between number of recruits and explanatory variables in 2 sets of models, which either included or excluded a linear trend across years in numbers of recruits. The best-performing models in each model set explained a substantial proportion of the variation in numbers of recrui...

The effects of heterospecifics and climatic conditions on incubation behavior within a mixed‐species colony

Parental incubation behavior largely influences nest survival, a critical demographic process in avian population dynamics, and behaviors vary across species with different life history breeding strategies. Although research has identified nest survival advantages of mixing colonies, behavioral mechanisms that might explain these effects is largely lacking. We examined parental incubation behavior using video‐monitoring techniques on Alcatraz Island, California, of black‐crowned night‐heron Nycticorax nycticorax (hereinafter, night‐heron) in a mixed‐species colony with California gulls Larus californicus and western gulls L. occidentalis. We first quantified general nesting behaviors (i.e. incubation constancy, and nest attendance), and a suite of specific nesting behaviors (i.e. inactivity, vigilance, preening, and nest maintenance) with respect to six different daily time periods. We employed linear mixed effects models to investigate environmental and temporal factors as sources of variation in incubation constancy and nest attendance using 211 nest days across three nesting seasons (2010–2012). We found incubation constancy (percent of time on the eggs) and nest attendance (percent of time at the nest) were lower for nests that were located &lt; 3 m from one or more gull nest, which indirectly supports the predator protection hypothesis, whereby heterospecifics provide protection allowing more time for foraging and other self‐maintenance activities. To our knowledge, this is the first empirical evidence of the influence of one nesting species on the incubation behavior of another. We also identified distinct differences between incubation constancy and nest attentiveness, indicating that these biparental incubating species do not share similar energetic constraints as those that are observed for uniparental species. Additionally, we found that variation in incubation behavior was a function of temperature and precipitation, where the strength of these effects was dependent on the time of day. Overall, these findings strengthen our understanding of incubation behavior and nest ecology of a colonial‐nesting species.