Showing papers in "Journal of Ornithology in 2012"

Morphometric indices of body condition in birds: a review

Abstract: Morphometric estimates of body condition are widely used by ornithologists, but which estimates work best is a matter of debate. We review morphometric approaches (body mass, ratio and residual condition indices, predictive regression models, fat scoring, and abdominal profiles) for estimating body condition (defined as fat mass) in birds. We describe the strengths and weaknesses of each approach. Across diverse indices and species (~200 estimates total), the mean r 2 relating condition indices to mass of body fat was 0.55, and 64% of the r 2 values were greater than 0.50. But despite their generally good performance, condition indices sometimes perform poorly (i.e., r 2 is low). The data indicate that: (1) no single index was clearly best, (2) on average body mass alone, fat scores, and predictive multiple regression equations explained slightly more than 50% of the variation in fat content, (3) on average, ratio and residual indices explained slightly less than 50% of the variation in fat content, and (4) body mass alone, a variable that can be easily and reliably measured, is as good or nearly as good an indicator of fat content as any other condition index. We recommend that: (1) morphometric indicators of condition be empirically validated, (2) researchers publish their body composition data in sufficient detail that they can be used in future analyses exploring the relative merits of different condition indices, and (3) multiple regression directly on measured traits be used instead of condition indices whenever the condition index is not empirically validated.

Comparison of model building and selection strategies

Abstract: One challenge an analyst often encounters when dealing with complex mark–recapture models is how to limit the number of a priori models. While all possible combinations of model structures on the different parameters (e.g., ϕ, p) can be considered, such a strategy often results in a burdensome number of models, leading to the use of ad hoc strategies to reduce the number of models constructed. For the Cormack–Jolly–Seber data type, one example of an ad hoc strategy is to hold a general ϕ model structure constant while investigating model structures on p, and then to hold the resulting best structure on p constant and investigate structures on ϕ. Many comparable strategies exist. The effect of following ad hoc strategies on parameter estimates as well as for variable selection and whether model averaging can ameliorate any problems are unknown. By means of a simulation study, we have investigated this informational gap by comparing the all-combinations model building strategy with two ad hoc strategies and with truth, as well as considering the results of model averaging. We found that model selection strategy had little effect on parameter estimator bias and precision and that model averaging did improve bias and precision slightly. In terms of variable selection (i.e., cumulative Akaike’s information criterion weights), model sets based on ad hoc strategies did not perform as well as those based on all combinations, as less important variables often had higher weights with the former than with the all possible combinations strategy. Increased sample size resulted in increased variable weights, with an infinite sample size resulting in all variable weights equaling 1 for variables with any predictive influence. Thus, the distinction between statistical importance (dependent on sample size) and biological importance must be recognized when utilizing cumulative weights. We recommend that all-combinations model strategy and model averaging be used. However, if an ad hoc strategy is relied upon to reduce the computational demand, parameter estimates will generally be comparable to the all-combinations strategy, but variable weights will not correspond to the all-combinations strategy.

Bird functional diversity and ecosystem services in tropical forests, agroforests and agricultural areas

Abstract: Although most bird species avoid agricultural areas, nearly a third of all birds regularly to occasionally use such habitats, often providing important ecosystem services like pest control, pollination, and seed dispersal. Combining literature review with large-scale analyses of the ecological characteristics of the world’s birds, I compared tropical bird species that prefer forests, agricultural areas or both, with respect to body mass, diet, range and population size, frequency, conservation status, habitat and resource specialization. Compared to primary forests, species richness of large frugivorous and insectivorous birds (especially terrestrial and understorey species) often declines in agroforests. In contrast, nectarivores, small-to-medium insectivores (especially migrants and canopy species), omnivores, and sometimes granivores and small frugivores do better, frequently by tracking seasonal resources. However, changes in guild species numbers do not necessarily translate to changes in relative abundance, biomass or function, and more studies are needed to quantify these important measures. These findings indicate that the replacement of forests and agroforests with simplified agricultural systems can result in shifts towards less specialized bird communities with altered proportions of functional groups. These shifts can reduce avian ecosystem function and affect the ecosystem services provided by birds in agroforests and other agricultural landscapes.

Parameter-expanded data augmentation for Bayesian analysis of capture–recapture models

Abstract: Data augmentation (DA) is a flexible tool for analyzing closed and open population models of capture–recapture data, especially models which include sources of hetereogeneity among individuals. The essential concept underlying DA, as we use the term, is based on adding “observations” to create a dataset composed of a known number of individuals. This new (augmented) dataset, which includes the unknown number of individuals N in the population, is then analyzed using a new model that includes a reformulation of the parameter N in the conventional model of the observed (unaugmented) data. In the context of capture–recapture models, we add a set of “all zero” encounter histories which are not, in practice, observable. The model of the augmented dataset is a zero-inflated version of either a binomial or a multinomial base model. Thus, our use of DA provides a general approach for analyzing both closed and open population models of all types. In doing so, this approach provides a unified framework for the analysis of a huge range of models that are treated as unrelated “black boxes” and named procedures in the classical literature. As a practical matter, analysis of the augmented dataset by MCMC is greatly simplified compared to other methods that require specialized algorithms. For example, complex capture–recapture models of an augmented dataset can be fitted with popular MCMC software packages (WinBUGS or JAGS) by providing a concise statement of the model’s assumptions that usually involves only a few lines of pseudocode. In this paper, we review the basic technical concepts of data augmentation, and we provide examples of analyses of closed-population models (M 0, M h, distance sampling, and spatial capture–recapture models) and open-population models (Jolly–Seber) with individual effects.

Adaptive phenological mismatches of birds and their food in a warming world

Abstract: Climate change has profound ecological effects in birds, with the clearest effect a shift in timing, or phenology, of avian reproduction. To assess the consequences of these shifts, we performed a literature search and compared the rates of phenological change in the reproduction of birds with that of the food for their offspring. While in some areas the rate of change of the birds and their food was similar, there were also areas where the birds’ shift lagged behind that of their food. In these cases, this will lead to a phenological mismatch, which will affect the fitness of the brood. There are two hypotheses explaining why climate change leads to mismatched reproduction: either the cues used no longer accurately predict the peak in food abundance (the cues hypothesis) or the fitness costs of egg production and/or incubation of laying early enough to match reproduction are substantial in early spring and are not compensated by the fitness benefits of a better matched reproduction (constraint hypothesis). In the latter case, the phenological mismatch is adaptive. We present a simple mathematical model to show that this may be the case if there are fitness costs of egg laying and/or incubation under cold conditions and if the temperatures that determine the peak in food abundance increase stronger than the temperatures affecting the costs of egg laying and incubation, as is the case in the Netherlands. Whether or not a phenological mismatch is adaptive has important consequences for natural selection acting on timing of reproduction. If the mismatch is not adaptive, timing of reproduction will be under direct natural selection, while, if the mismatch is adaptive, selection is likely to be on the costs of egg production, possibly on egg size or adult size. In all cases, a mismatch is expected to have negative population consequences and, especially when the mismatch is adaptive, these consequences cannot be reduced by a response to natural selection on timing directly. This makes experimental studies on laying date, which can determine whether the mismatch is adaptive, of crucial importance.

Revealing the contributions of reproduction and survival to the Europe-wide decline in meadow birds: review and meta-analysis

Abstract: In this review, we summarize available data on nest success, chick survival and reproductive output, and adult and juvenile survival of five meadow breeding waders in Europe: Eurasian Oystercatcher (Haematopus ostralegus), Northern Lapwing (Vanellus vanellus), Black-tailed Godwit (Limosa limosa), Eurasian Curlew (Numenius arquata), and Common Redshank (Tringa totanus). The survival data from the assembled studies did not show an overall decline in adult survival in any of these species. However, our meta-analyses on reproduction data show that chick survival declined strongly in the last 40 years in western Europe and that nest success declined in eastern Europe in the period 1995–2005, in Scandinavia in the period 1985–2005, and in western Europe in the period 1950–1980. Predation of nests has increased by c. +40% in all five species in western Europe during the last four decades. Results on reproductive output, the number of fledglings produced per breeding pair, were less clear. A decline was apparent in Eurasian Oystercatcher in the period 1963–2005; an initial decline in 1953–1990, but slight recent (1990–2006) recovery in Northern Lapwing; an initial decline in Black-tailed Godwit in the period 1985–1995, but again slight increase from 1995 onwards; no trend in Common Redshank (1992–2006) nor in Eurasian Curlew (1961–2006). In all five species the results indicate that present population declines are caused by a decrease in reproduction, not in adult survival, and that reproductive output is presently too low to compensate for adult mortality.

A non-technical overview of spatially explicit capture–recapture models

Abstract: Most capture–recapture studies are inherently spatial in nature, with capture probabilities depending on the location of traps relative to animals. The spatial component of the studies has until recently, however, not been incorporated in statistical capture–recapture models. This paper reviews capture–recapture models that do include an explicit spatial component. This is done in a non-technical way, omitting much of the algebraic detail and focussing on the model formulation rather than on the estimation methods (which include inverse prediction, maximum likelihood and Bayesian methods). One can view spatially explicit capture–recapture (SECR) models as an endpoint of a series of spatial sampling models, starting with circular plot survey models and moving through conventional distance sampling models, with and without measurement errors, through mark–recapture distance sampling (MRDS) models. This paper attempts a synthesis of these models in what I hope is a style accessible to non-specialists, placing SECR models in the context of other spatial sampling models.

A rapid effect of handling on counts of white blood cells in a wintering passerine bird: a more practical measure of stress?

Abstract: Measuring circulating glucocorticoids is a widely used method to assess stress in animals. However, hormones must be sampled within the first few minutes of capture, which makes it difficult to discriminate between hormone baseline levels and the levels caused by capture and handling stress. The use of white blood cell (WBC) counts made from blood smears represents an alternate method for measuring physiological stress. Since the increase in glucocorticoid hormones causes characteristic long-lasting changes in the leukocyte numbers, we tested whether stress-related handling of male Great Tits (Parus major) may cause rapid changes in their leukocyte profile. We found that handling stress significantly increased heterophil counts between 30 and 60 min after capture, while lymphocyte and eosinophil counts significantly declined between 60 and 120 min after capture. The increase in heterophil counts and reduction in lymphocyte counts caused an increase of the heterophil and lymphocyte ratio (H/L) between 60 and 120 min after capture. Overall, these results indicate that leukocyte profiles in wintering male Great Tits may change more rapidly than previously thought, reflecting acute stress of individual birds.

Obligate and facultative migration in birds: ecological aspects

Abstract: This paper is concerned mainly with the differences between obligate and facultative migration in birds. Obligate migration is considered “hard-wired”, in that the bird seems pre-programmed to leave its breeding area at a certain time each year, and to return at another time. Timing, directions and distances are relatively constant from year to year. This type of migration is thus characterised by its regularity, consistency and predictability. It is found in both short-distance and long-distance migrants, but mainly in the latter. In contrast, facultative migration is considered optional, occurring in response to conditions at the time. Individuals may migrate in some years but not in others, depending on the prevailing food supplies or weather conditions. The timing of autumn migration, and the distance travelled, can be highly variable between individuals and, at the population level, between years. Facultative migration is typical of many partial migrants, but is found in its most extreme form in so-called irruptive migrants. While individual obligate migrants typically return to the same breeding localities year after year, and sometimes also to the same wintering localities, individual irruptive migrants typically breed or winter in widely separated areas in different years, wherever conditions are favourable. It is suggested that these two types of migration are best considered not as distinct, but as lying at opposite ends of a continuum of variation in bird migratory behaviour. Both systems are adaptive; one to conditions in which resource levels vary regularly and predictably in space and time, and the other to conditions in which resource levels vary unpredictably. Suggestions are made for experimental work on captive irruptive species.

The effect of an external transmitter on the drag coefficient of a bird’s body, and hence on migration range, and energy reserves after migration

Abstract: Externally mounted transmitters or loggers may adversely affect migration performance for reasons other than the effects of added mass. The added frontal area of a payload box increases drag, and if the box triggers separation of the boundary layer over the posterior body, the drag coefficient could also be increased, possibly by a large amount. Any such effects would lead directly to a decreased migration range and reduced energy reserves on completion of migration. We measured the body drag coefficients of Rose-coloured Starlings in the Seewiesen wind tunnel by the wingbeat-frequency method. The speed at which the wingbeat frequency passed through a minimum was taken to be an estimate of the minimum-power speed (V mp), from which the body drag coefficient was calculated in turn. Dummy transmitter boxes were mounted on the bird’s back by attaching them with Velcro to a side-loop harness pad. The pad alone projected 6 mm above the bird’s back, and increased the drag coefficient by nearly 50%, as compared to the “clean” configuration with no harness. Adding boxes (square-ended or streamlined) produced no further significant increase in the drag coefficient, but the addition of a sloping antenna increased it to nearly twice the clean value. These increases are attributed to separation of the boundary layer over the posterior upper body, triggered by the payload. We then ran computer simulations of a particular Barnacle Goose, for which detailed information was available from an earlier satellite-tracking project, to see how its migration range and reserves on arrival would be affected if its transmitter installation also caused flow separation and affected the body drag coefficient in a similar way. By representing the range calculation in terms of energy height, we separated the effect of the transmitter’s mass, which reduces the fat fraction (and hence also energy height) at departure, from that of flow separation, which steepens the energy gradient. The effect of the mass is small, and increases only slightly with increasing distance, whereas a steeper energy gradient not only reduces the range but also reduces the reserves remaining on arrival, to an extent that increases with migration distance. Energy height is related to the fat fraction rather than the fat mass, and is therefore preferable to energy as such, for expressing reserves in birds of different sizes.

Nest sanitation in passerine birds: implications for egg rejection in hosts of brood parasites

Abstract: We reviewed information on nest sanitation (nest cleaning) by passerine birds because the act of cleaning nests is thought to be associated with egg rejection by hosts of brood parasites, and yet there has been no synthesis of the literature on nest sanitation. In the first part of the review, we summarized information on nest sanitation. We found that birds remove a variety of objects from nests such as egg shells, fecal sacs, pieces of vegetation, invertebrate parasites, dead chicks, uneaten food, and occasionally unhatched eggs. Fecal sac removal, the most commonly considered type of nest sanitation behavior, is not divided equally between the sexes across species; females remove more fecal sacs than males. In addition, larger species tend to carry fecal sacs farther than smaller species. In the second part of the review, we discuss the importance of nest sanitation in the evolution of egg rejection behavior of brood parasite hosts. Recent studies involving the experimental addition of non-egg-shaped objects to nests or to the vicinity of nests suggest that nest sanitation plays a role in host rejection of avian brood parasitism. Most objects added to nests prior to hatching (usually hard) and after hatching (usually soft) were rejected. In a logistic regression model, shape and size were the significant factors in eliciting rejection for all hosts that received experimental non-egg objects added to their nests prior to hatching. Nest sanitation may be an exaptation for antiparasite defences and thus plays an important role in the host-parasite arms race.

Disease dynamics in wild populations: modeling and estimation: a review

Abstract: Models of infectious disease dynamics focus on describing the temporal and spatial variations in disease prevalence, and on understanding the factors that affect how many cases will occur in each time period and which individuals are likely to become infected. Classical methods for selecting and fitting models, mostly motivated by human diseases, are almost always based solely on raw counts of infected and uninfected individuals. We begin by reviewing the main classical approaches to parameter estimation, and some of their applications. We then review recently developed methods which enable representation of component processes such as infection and recovery, with observation models that acknowledge the complexities of the sampling and detection processes. We demonstrate the need to account for detectability in modeling disease dynamics, and explore a number of mark–recapture and occupancy study designs for estimating disease parameters while simultaneously accounting for variation in detectability. We highlight the utility of different modeling approaches and also consider the typically strong assumptions that may actually serve to limit their utility in general application to the study of disease dynamics (e.g., assignment of individuals to discrete disease states when underlying state space is more generally continuous; transitions assumed to be simple first-order Markov; temporal separation of hazard and transition events).

Floral resource availability and hummingbird territorial behaviour on a Neotropical savanna shrub

Abstract: The influence of floral resource availability on behaviour and dominance hierarchy of hummingbirds has seldom been investigated in open tropical environments. We evaluated the behavioural changes of hummingbirds associated with Palicourea rigida, a shrub common in the Cerrado, the open savanna areas in Central Brazil. We observed the foraging behaviour as a function of resource availability and experimentally manipulated floral display and nectar in order to define resource thresholds associated with territorial behaviour and territory intruding behaviour. Territorial behaviour was observed only in patches with high floral abundance and was restricted to some hummingbird species. The large Eupetomena macroura seems to be the dominant species in the community, excluding other hummingbirds and holding the richest patches. The experimental reduction in the floral abundance and nectar led to the abandonment of territory by these hummingbirds, which reinforces the idea that a certain threshold is necessary to maintain territorial defence. Higher floral display, on the other hand, seems to lead to higher frequency of intrusions and higher behavioural complexity of territory defenders, possibly meaning greater energy expenditure. The flower number and nectar manipulation affected visitation rates of territorial hummingbirds, but the frequency of intruders was affected only by the former manipulation. This indicates that territorial intruder use visual cues (floral abundance) as indicators of resource availability in order to estimate cost–benefit of territory invasion. Although territorial behaviour could limit pollen flow in patches with larger floral displays, this may be compensated by the territory invaders, which bring pollen from other patches.

Habitat at the mountain tops: how long can Rock Ptarmigan (Lagopus muta helvetica) survive rapid climate change in the Swiss Alps? A multi-scale approach

Abstract: Ongoing monitoring in the Swiss Alps has shown that Rock Ptarmigan (Lagopus muta helvetica) has suffered a significant population decrease over the last decade and climate change has been proposed as a potential cause. In this study, we investigate the response of this high alpine grouse species to rapid climate change. We address a problem often neglected in macro-ecological studies on species distribution: scale-dependency of distribution models. The models are based on empirical field data and on environmental databases for large-scale models. The implementation of several statistical modelling approaches, external validation strategies and the implementation of a recent study on regional climate change in Switzerland ensure robust predictions of future range shifts. Our results demonstrate that, on the territory level, variables depicting vegetation, heterogeneity of local topography and habitat structure have greatest explanatory power. In contrast at the meso-scale and macro-scale (with grain sizes of 1 and 100 km2, respectively), bioclimatic and land cover-related variables play a prominent role. The models predict that, based on increasing temperatures during the breeding season, potential habitat will decrease by up to two-thirds until the year 2070. At the same time, a shift of potential habitat towards the mountain tops is predicted. The multi-scale approach highlights the true extent of potential habitat for this species with its patchy distribution in steep terrain. The small-scale analysis pinpoints the key habitat areas within the extensive areas of suitable habitat predicted by models on large grain sizes and in this way reveals sub-grid variability. Our results can facilitate the adaptation of species conservation strategies to a quickly changing environment.

Through birds’ eyes: insights into avian sensory ecology

Abstract: Sensory ecology investigates the information that underlies an animal’s interactions with its environment. A sensory ecology approach provides a framework in which to investigate a wide range of topics in ornithology. This review provides a range of examples of this approach. Discussed are some of the more general principles which apply with respect to the ways in which information from different sensory systems may complement each other, or information is traded-off within a sensory modality in the achievement of particular tasks. The emphasis is upon the task of foraging, but other behaviours, such as locomotion and predator detection, are also addressed. Examples discussed consider: (1) the perceptual challenges of nocturnal activity and how they are differently solved by information from different sensory system in owls, kiwi, oilbirds and penguins; (2) the use of tactile information in foraging and how this interacts with visual information in probing birds, and in skimmers; and (3) the visual information used to guide stealth foraging in herons, and how vision is influenced by the filter feeding techniques of ducks and flamingos. In addition, two case studies are discussed. These explore: (a) the restrictions on the information available to guide foraging in turbid waters by cormorants, and (b) the application of a sensory ecology approach to understanding why birds collide with artefacts, such as power lines and wind turbines, which intrude into the open airspace. Among the general conclusions discussed are: (1) the idea that all sensory systems are selective within their own modality and that the range of information that is available to a particular species have been tuned to particular perceptual challenges through natural selection; it is also argued that this tuning can take place at the individual species level such that there may be key differences in sensory information even among birds in the same genus; (2) sensory systems detect only a small part of the total information that is available in the environment; no species has available to it all the information that is potentially available in its environment; in essence, all species share the same planet but live in different worlds that are dictated by the information that their sensory systems extract from the environment; (3) there may be complex and subtle trade-offs between different types of sensory information; and (4) the overall conclusion is that the world through birds’ eyes is quite different from the world as seen through human eyes but there are many different “bird eye views”.

A review of designs for capture–mark–recapture studies in discrete time

Abstract: Design is the most influential element in the pathway to statistical inference. Designs for capture–mark–recapture (CMR) studies have become more diverse and complex during the past 50 years. I review the history of CMR designs developed for discrete time models with a focus on the assumptions of those designs, the parameters that can be estimated, the question that can be addressed, and the interrelationship among designs. CMR designs can be used to address questions in a variety of disciplines including population dynamics, evolutionary ecology, life-history, and community ecology. Methodological advances have also enabled investigators to consider designs that include nearly all common sources of CMR data simultaneously. CMR designs have been generalized to account for many assumptions; however, more emphasis needs to placed on use of auxiliary variables to increase precision and address model assumptions. CMR designs also need to be placed in the larger context of experimentation. Finally, development of more specific designs to fully utilize data resulting from emerging technologies is needed.

From NOREMARK to MARK: software for estimating demographic parameters using mark–resight methodology

Abstract: Mark–resight methods can be a less expensive and less invasive alternative to traditional mark–recapture for estimating abundance and related demographic parameters. This is because only a single marking event is required, and subsequent sighting data from both marked and unmarked individuals are used for estimation. Mark–resight is therefore particularly appealing when working with limited budgets or sensitive species. These methods have been applied to many taxa, including avians such as Bald Eagles (Haliaeetus leucocephalu), Sage Grouse (Centrocercus urophasianus), and New Zealand Robins (Petroica australis). However, previous model and software development overwhelmingly focused on abundance estimation and did not extend much beyond classic Lincoln–Petersen methods. For this purpose, Program NOREMARK provided a convenient, but limited, means for analysis. To address these limitations, a new suite of likelihood-based mark–resight estimators has been developed and implemented within Program MARK. Unlike the estimators in NOREMARK, these new models provide a theoretical basis for model selection and multimodel inference, the incorporation of spatio-temporal and individual covariate information, full utilization of the robust design (including the estimation of survival and state transition probabilities), and all the other analysis tools that MARK provides. In addition, MARK no longer requires that the exact number of marked individuals available for sighting be known, thereby greatly extending the potential use of mark–resight methodology for population monitoring. Here, we provide a review of mark–resight methodology and present the various mark–resight estimators that are implemented in Program MARK.

Adaptive hypotheses for protandry in arrival to breeding areas: a review of models and empirical tests

Abstract: Our understanding of avian migration has progressed significantly, yet the selective conditions that favor the arrival of males before females at the site of reproduction remain largely unclear. Here, we review the leading adaptive hypotheses for protandry, highlight some key empirical studies that test protandry theory, and identify theoretical and empirical information demands. In general, protandry should evolve in species where the variance in male reproductive success is larger than in females if the costs to males of earlier arrival relative to calendar date (viability selection) can be balanced by increased mating opportunities (sexual selection). Early arrival by males can provide ‘priority benefits’ that help in the monopolization of resources or ‘early bird draw benefits’ that increase opportunities for extra-pair mating. While some empirical studies are consistent with theoretical predictions regarding the important selection factors that influence protandry (e.g., extrinsic mortality and extra-pair paternity), some are not, and some studies focus on ecological factors that have not been considered explicitly by theory. We call for an integrated theoretical approach to help formalize how protandry should evolve in response to the antagonistic roles of natural and sexual selection, the nature of competitive asymmetries among males or females, sex-specific costs and benefits of early arrival, and various climate change scenarios.

How would size, age, human disturbance, and vegetation structure affect bird communities of urban parks in different seasons?

Abstract: Parks are diversity hotspots in cities, and are generalized isolated “islands” in urban landscapes. However, there is a paucity of information on the avian community structure of urban parks in big cities in Southeast Asia, including Hong Kong which has more than 7 million people. This study therefore aimed to assess the influences of park attributes, human disturbance, and vegetation structure on species richness, diversity, total density, and species groups of breeding and wintering bird communities in Hong Kong. Bird communities of 30 parks were censused four times each season in 2010–2011 using point counting. Species richness and diversity were affected by park size in both seasons, and larger parks supported more species and higher diversity. In addition, species richness of wintering season was negatively affected by visitor rate. Total bird density increased with visitor rate, but only in the breeding season. Noise did not have significant impacts on species richness, diversity, and total density. Regarding the responses of species groups, number of resident species increased with park size in both seasons. Migrants, insectivores, and insectivore–frugivores were positively affected by park size, but negatively by visitor rate in the wintering season. However, omnivores in the breeding season increased with both park size and visitor rate. Granivores was the only feeding guild which was positively affected by noise and negatively by foliage height diversity in the wintering season. In conclusion, park size and visitor rate affected bird community structure, and different species groups had different responses to habitat factors in the two seasons.

Nest box design for the study of diurnal raptors and owls is still an overlooked point in ecological, evolutionary and conservation studies: a review

Abstract: The use of artificial nest boxes has led to significant progress in bird conservation and in our understanding of the functional and evolutionary ecology of free-ranging birds that exploit cavities for roosting and reproduction. Nest boxes and their improved accessibility have made it easier to perform comparative and experimental field investigations. However, concerns about the generality and applicability of scientific studies involving birds breeding in nest boxes have been raised because the occupants of boxes may differ from conspecifics occupying other nest sites. Here, we review the existing evidence demonstrating the importance of nest box design to individual life-history traits in three falcon (Falconiformes) and seven owl (Strigiformes) species, as well as the extent to which publications on these birds describe the characteristics of exploited artificial nest boxes in their "Methods" sections. More than 60% of recent publications did not provide any details on nest box design (e.g. size, shape, material), despite several calls >15 years ago to increase the reporting of such information. We exemplify and discuss how variation in nest box characteristics can affect or confound conclusions from nest box studies and conclude that it is of overall importance to present details of nest box characteristics in scientific publications.

Terns in trouble: demographic consequences of low breeding success and recruitment on a common tern population in the German Wadden Sea

Abstract: The nationally endangered breeding population of Common Terns Sterna hirundo in the German Wadden Sea has been rapidly declining in recent years. In an attempt to identify the causes for this decline we analysed the demography of the Jade Bay population based on the “Banter See” colony. This colony has been intensively studied for over 18 years and has been declining in recent years. We estimated apparent survival rates of breeders and non-breeders of different ages using multi-state capture–recapture models based on individual life histories. The population growth rates of the Banter See colony and Lower Saxony population were estimated, and possible future trajectories were projected using a matrix model approach. Adult survival rates (0.9) have remained constant, but since 2002 subadult survival has decreased significantly (0.36–0.28). We found significantly lower breeding success as well as lower and delayed recruitment. These changes in vital rates probably caused the shift in the Banter See colony growth rate from an increasing phase before 2002 to a declining phase after and most likely occurred due to low pelagic prey fish stocks in the North Sea, the most important food source for terns in the Wadden Sea. Should the population decline continue at the current rates, the Banter See colony could decrease by 11% and the Lower Saxony Wadden Sea population by an alarming 57% between 2009 and 2015. Zusammenfassung Seeschwalben mit Problemen: Demographische Konsequenzen von geringem Bruterfolg und geringer Rekrutierung in einer Flussseeschwalben-Population im Deutschen Wattenmeer Die Brutpopulation der Flussseeschwalbe Sterna hirundo im niedersachsischen Wattenmeer hat in den letzten Jahren einen starken Ruckgang erfahren. Diese Entwicklung ist bedenklich, da diese Art seit 2007 auf der Roten Liste als stark gefahrdet eingestuft wird. Um Ursachen fur den Ruckgang in der Zahl der Brutpaare festzustellen, wurde in dieser Studie die Demographie der Flussseeschwalbenpopulation am Jadebusen untersucht, mit besonderem Augenmerk auf die Kolonie „Banter See“ in Wilhelmshaven. Diese Kolonie wird seit uber 18 Jahren eingehend untersucht und zeigt ebenfalls einen rucklaufigen Trend. Uberlebensraten von Brutern und Nichtbrutern verschiedener Altersgruppen wurden anhand eines Multi-State Capture–Recapture Modells, basierend auf individuellen Lebensgeschichten, ermittelt. Die Wachstumsrate der Banter See Kolonie wurde in zwei Phasen unterteilt: eine wachsende Phase vor 2002 und eine abnehmende Phase danach. Diese Entwicklung wurde durch Anderungen in wesentlichen demographischen Raten hervorgerufen, so wie signifikant geringerer Bruterfolg, signifikant weniger und spatere Rekrutierung und signifikant geringere Uberlebensraten zweijahriger Vogel seit 2002 (von 36% auf 29%). Die Uberlebensraten adulter Vogel (90%) dagegen blieben in dieser Zeit konstant. Die Anderungen in demographischen Raten ist hochstwahrscheinlich auf niedrige Herings—Clupea harengus und Sprottenbestande Clupea sprattus in der Nordsee zuruckzufuhren, die die wichtigste Nahrungsquelle fur Seeschwalben im Wattenmeer darstellen. Andere Flussseeschwalbenkolonien im Wattenmeer erlebten einen wesentlich schlimmeren Ruckgang in der Zahl der Brutpaare und haben begonnen sich aufzulosen. Sollte der Ruckgang der Brutpaare im derzeitigen Ausmas weitergehen, konnte sich die Banter See Kolonie bis 2015 um bis zu 11% der Brutpopulation von 2009 verringern, wahrend die gesamte Wattenmeer Population in der Zeit sogar um alarmierende 57% der Bestande von 2008 abzunehmen droht.

A matter of history: effects of tourism on physiology, behaviour and breeding parameters in Magellanic penguins ( Spheniscus magellanicus ) at two colonies in Argentina

Abstract: Increasing ecotourism activity in Argentine Patagonia has led to concerns about the effects of ecotourism on wildlife populations Penguin breeding colonies are popular tourist destinations While some species of penguins habituate to human visits, others exhibit negative effects due to disturbance We studied the effects of tourism on Magellanic Penguins (Spheniscus magellanicus) at San Lorenzo colony located on the Peninsula Valdes, Chubut, Argentina We measured behavioural, physiological, and reproductive parameters in birds nesting in tourist-visited and non-visited areas San Lorenzo has 11 years of visitation history and a low intensity of visitors (~10,000 annually) After 15 min of a simulated tourist visit, penguins in the tourist area showed fewer alternate head turns and lower plasma levels of the stress hormone corticosterone than penguins in a non-visited area However, penguins showed similar baseline levels of corticosterone between areas as well as similar levels of integrated corticosterone expressed after an acute stressor Penguin breeding success and chick growth were similar between areas We compared these findings to results previously published from Punta Tombo, a colony with a longer history (+50 years) and high intensity of annual visitors (>120,000 people) Many (reproductive and behavioural parameters), but not all (physiological parameters), of our findings are similar That a physiological difference exists may suggest that the previous history of human visitation plays an important role in the response of the birds Thus, the continuous monitoring of tourist activity is important, as a history of visitation disturbance seems to have an effect on how birds respond to tourists

Developmental stress and birdsong: current evidence and future directions

Abstract: The developmental stress hypothesis posits that the honesty of bird song is maintained by costs incurred during development, rather than at the time of adult song production. Song is learned, and the neural systems underlying song learning and production develop early in life at a time when nutritional and other stressors are prominent. Thus, adult song may reflect the early developmental conditions of a male and/or how well that male was able to cope with developmental stressors. Substantial evidence in support of the developmental stress hypothesis has accrued over the last decade, but much remains to be done. Here, we review the current evidence in support of the hypothesis and highlight future directions. With few exceptions, there is now solid evidence that a variety of developmental stressors impair development of song and the brain. We note that birdsong is potentially an example of a larger class of sexually-selected indicators of developmental conditions. Future issues include examining the effects of stress on females, resolving whether song indicates developmental stability or developmental environment, exploring the neuroendocrine mechanisms by which stress modifies song development, determining whether stressed birds are subject to phenotypic programming, and determining the effects of stressors on song in adult birds. The developmental stress hypothesis thus provides a rich framework for future integrative studies of birdsong and development.

Delayed autumn migration in northern European waterfowl

Abstract: Climate change is causing phenological shifts in the environment. Among birds, increasing temperatures have been shown to advance the spring migration and breeding, which in turn affect individual reproductive success. The autumn migration phenology has, however, been largely overlooked. Here, we study long-term changes in the timing of autumn migration in 15 northern European waterfowl species during 1979–2009. We hypothesised that waterfowl should delay their migration since they winter north of the Sahara desert. Our results show that 6 (Greylag Goose Anser anser, Eurasian Wigeon Anas penelope, Eurasian Teal Anas crecca, Tufted Duck Aythya fuligula, Velvet Scoter Melanitta fusca, and Common Goldeneye Bucephala clangula) of the 15 studied species have delayed at least one of the three phases of migration examined. The most marked delay in median migration dates was by more than a month over the past 31 years. Only the Bean Goose Anser fabalis exhibited an advanced beginning of its migration. We also analyse the timing of the entire waterfowl migration and show that the median and end of the migration have been significantly delayed. The results support our predictions and highlight how rapid phenological responses to climate change may be. Such delayed departures may be the cause for recently observed northward shifts of wintering ducks. Our results suggest that waterfowl to be a good indicator group for climate change. Changing migration times can also have population-level consequences due to differential hunting and natural predation pressures over the waterfowl flyway.

Physiological and behavioral responses of migrants to environmental cues

Abstract: Migrant species express wide varieties of movement strategies that closely mirror patterns of resource distribution. Resources can vary predictably in space and time (e.g., seasonal peaks of productivity in temperate regions) or can be unpredictable in one or both dimensions. Evolution of migration strategies and the underlying physiological and behavioral mechanisms are therefore diverse, but similarities have been noted. To understand how migrants respond to environmental cues, we focus on species that represent extremes along a continuum between obligate versus facultative migratory behavior and address the physiological mechanisms regulating these movements. Obligate migrants, which travel on highly predictable schedules, generally rely on the annual change in daylength and circannual rhythms to initiate the vernal and, where known, the fall phases of migration. Facultative species may show similar seasonal preparations in cases where resources are temporally predictable, but appear to rely more heavily upon local supplementary cues in the environment to initiate migrations. In general, the physiological response mechanisms to environmental cues that coordinate migratory movements include perception of the environmental cue and transduction to neuroendocrine and endocrine systems. Clearly, there are huge gaps in our knowledge in this area, but published studies of each of the migratory types suggest striking parallels. Based on a comparison of the physiological aspects of the divergent migratory patterns, we emphasize that the migratory types are not completely distinct. Instead, the differences of migration patterns and responsiveness to cues reflect differences in the relative contributions of common physiological mechanisms that underly the control of movements. A more complete understanding of migratory physiology requires continued descriptive studies, particularly in a greater diversity of model systems, in addition to experimental methods that utilize innovative tracking technology as well as behavioral and physiological innovations to draw attention to different levels of organization. Comprehending the physiological mechanisms underlying migratory patterns will be vital for knowing how migrants respond to current environmental cues and anticipating their reactions to future conditions.

Nest size and breeding success in first and replacement clutches: an experimental study in Blue Tits Cyanistes caeruleus

Abstract: Bird nests function to protect parents, eggs or offspring against fluctuations in the environment. In Blue Tits (Cyanistes caeruleus) producing first or replacement clutches, we examined relationships between nest height (a measure of nest size) and several parameters of breeding performance that are often quantified in long-term avian field studies. We artificially increased the cost of reproduction in randomly selected females by removing the whole first clutch and nest material after about 5 days of incubation. This experiment resulted in replacement nests. Experimentally increasing the range of breeding conditions across females, we expected to have more power to detect a positive correlation between nest height and breeding success. However, we found that nest height was not significantly related to any of the breeding traits investigated (clutch size, number of hatchlings, number of fledglings, hatching success, fledging success, chick mass), after controlling for factors frequently investigated in long-term monitoring programs and known to influence breeding performance (female age, year, clutch type as a proxy of egg-laying date). We conclude that the identification of the exact underlying mechanisms causing relationships between nest characteristics and breeding performance will require more experimental study and the exploitation of larger datasets, both within and across avian model systems.

Investigating the population dynamics of California spotted owls without marked individuals

Abstract: Understanding population dynamics is of great interest in many different contexts. Traditionally, population dynamics have often been considered in terms of individual-based demographic parameters (e.g., abundance, survival, and reproductive rates), estimation of which generally requires information from marked individuals. Alternatively, in some situations, it may be appropriate to consider population dynamics at a landscape level where the focus is shifted from numbers of individuals to the status of the population at places on the landscape. One consequence of doing so is that information from marked individuals is no longer required. Recently developed methods allow the estimation of landscape-level population vital rates in the realistic situation where the current status of the population might be misclassified via field methods (e.g., because of imperfect detection). Here, we consider the case of the California spotted owl (Strix occidentalis occidentalis) at the Eldorado study area in central Sierra Nevada, California, USA, where interest is in the occupancy rate of potential nesting territories, and in whether owls in an occupied territory successfully reproduced each year during 1997–2004. We analyzed the data using multistate occupancy models and found no evidence of annual variation in dynamic occupancy probabilities. There was strong evidence of annual variation in successful reproduction, with the pattern of variation being different depending on whether there was successful reproduction in the territory in the previous year. Of the three environmental variables considered, the Southern Oscillation Index appeared to be most important and explained some of the annual variation in reproduction probabilities.

Spatially explicit capture?recapture methods to estimate minke whale density from data collected at bottom-mounted hydrophones

Abstract: Estimation of cetacean abundance or density using visual methods can be cost-ineffective under many scenarios. Methods based on acoustic data have recently been proposed as an alternative, and could potentially be more effective for visually elusive species that produce loud sounds. Motivated by a dataset of minke whale (Balaenoptera acutorostrata) “boing” sounds detected at multiple hydrophones at the U.S. Navy’s Pacific Missile Range Facility (PMRF), we present an approach to estimate density or abundance based on spatially explicit capture–recapture (SECR) methods. We implement the proposed methods in both a likelihood and a Bayesian framework. The point estimates for abundance and detection parameters from both implementation methods are very similar and agree well with current knowledge about the species. The two implementation approaches are compared in a small simulation study. While the Bayesian approach might be easier to generalize, the likelihood approach is faster to implement (at least in simple cases like the one presented here) and more readily amenable to model selection. SECR methods seem to be a strong candidate for estimating density from acoustic data where recaptures of sound at multiple acoustic sensors are available, and we anticipate further development of related methodologies.

The two hemispheres of the avian brain: their differing roles in perceptual processing and the expression of behavior

Abstract: The hemispheres of the avian brain are specialized to carry out different functions. Since each eye sends its input mainly to the contralateral hemisphere, birds respond differently to stimuli seen with the left eye than they do to stimuli seen with the right eye. The right hemisphere attends to novel stimuli, which easily distract it from ongoing functions. It assumes control in emergency or stressful conditions. The left hemisphere attends to learnt categories and controls behavior in routine, non-stressful situations. This division of function extends to processing of auditory, olfactory and even magnetic stimuli. Evidence for this comes from a number of avian species, and has been shown in both laboratory and field tests. Knowledge of these specializations is relevant to understanding the behavior of birds in the wild since birds respond in different ways to stimuli on their left and right sides (e.g. preferential response to predators and conspecific on the left side and to prey on the right side) and they choose to view different stimuli with the left or right eye. Individual differences in the strength of visual lateralization are determined by exposure of the embryo to light, versus incubation in the dark, and by the levels of steroid hormones in ovo. The importance of these influences on lateralization is discussed in terms of behavior in the natural habitat. The potential importance of hemispheric dominance in the welfare of birds is also considered.

Landscape structure, human disturbance and crop management affect foraging ground selection by migrating geese

Abstract: It is well known that agricultural intensification has caused severe population declines among bird species which use farmland for breeding and overwintering, while migrating bird species may benefit from intensive farming, but in turn damage crops. Knowledge of the habitat selection of migrating birds is important from both a conservation and agro-economic point of view. We investigated the habitat preferences of three common migrating goose species: White-fronted Goose Anser albifrons, Bean Goose A. fabalis and Greylag Goose A. anser during the autumn of 2009 in western Poland. A total of 24 flocks of these species were identified. Geese preferred large, elevated fields that were remote from forests and human settlements but in close proximity to a lake. Geese selected maize stubbles and avoided winter cereals. They selected sites in landscapes with a lower diversity of crops. Flock size was negatively correlated with the proportion of pastures in the landscape, but it increased with field size, distance to forest and distance to town. Our results are in contrast with the paradigm that less intensive farmland positively influences habitat use by birds during foraging. We advise the delayed ploughing of stubbles with the aim of creating appropriate foraging habitats for geese and minimizing damage to cereal crops.