Biology subjects

Valcu, M.

Publications and source records attributed to Valcu, M..

8 recordsLinked to original sources

bioRxiv2021

Still no evidence for disruption of global patterns of nest predation in shorebirds

Many shorebird species are rapidly declining (Piersma et al. 2016; Munro 2017; Studds et al. 2017), but it is not always clear why. Deteriorating and disappearing habitat, e.g. due to intensive agriculture (Donal et al. 2001; Kentie et al. 2013; Kentie et al. 2018), river regulation (Nebel et al. 2008) or mudflat reclamation (Ma et al. 2014; Larson 2017), and hunting (Reed et al. 2018; Gallo-Cajiao et al. 2020) are some of the documented causes. A recent study suggests yet another possible cause of shorebird decline: a global increase in nest predation (Kubelka et al. 2018). The authors compiled an impressive dataset on patterns of nest predation in shorebirds and their analyses suggest that global patterns of nest predation have been disrupted by climate change, particularly in the Arctic. They go as far as to conclude that the Arctic might have become an ecological trap (Kubelka et al. 2018). Because these findings might have far-reaching consequences for conservation and related political decisions, we scrutinized the study and concluded that the main conclusions of Kubelka et al. (2018) are invalid (Bulla et al. 2019a). The authors then responded by reaffirming their conclusions (Kubelka et al. 2019b). Here, we evaluate some of Kubelka et al.s (2019b) responses, including their recent erratum (2020), and show that the main concerns about the original study still hold. Specifically, (1) we reaffirm that Kubelka et al.s (2018) original findings are confounded by study site. Hence, their conclusions are over-confident because of pseudo-replication. (2) We reiterate that there is no statistical support for the assertion that predation rate has changed in a different way in the Arctic compared to other regions. The relevant test is an interaction between a measure of time (year or period) and a measure of geography (e.g., Arctic vs the rest of the world). The effect of such an interaction is weak, uncertain and statistically non-significant, which undermines Kubelka et al.s (2018) key conclusion. (3) We further confirm that the suggested general increase in predation rates over time is at best a weak and uncertain trend. The most parsimonious hypothesis for the described results is that the temporal changes in predation rate are an artefact of temporal changes in methodology and data quality. Using only high-quality data, i.e. directly calculated predation rates, reveals no overall temporal trend in predation rate. Below we elaborate in detail on each of these points. We conclude that (i) there is no evidence whatsoever that the pattern in the Arctic is different from that in the rest of the world and (ii) there is no solid evidence for an increase in predation rate over time. While we commend Kubelka et al. for compiling and exploring the data, we posit that the data underlying their study, and perhaps all currently available data, are not sufficient (or of sufficient quality) to test their main hypotheses. We call for standardized and consistent data collection protocols and experimental validation of current methods for estimating nesting success.

ecology↗

bioRxiv2020

A global analysis of song frequency in passerines provides no support for the acoustic adaptation hypothesis but suggests a role for sexual selection

Many animals use acoustic signals for communication, implying that the properties of these signals can be under strong selection. The acoustic adaptation hypothesis predicts that species living in dense habitats emit lower-frequency sounds than those in open areas, because low-frequency sounds generally propagate further in denser vegetation. Signal frequency may also be under sexual selection, because it correlates with body size and lower-frequency sounds are perceived as more intimidating. Here, we evaluate these hypotheses by analysing variation in peak song frequency across 5,085 passerine species (Passeriformes). A phylogenetically-informed analysis revealed that song frequency decreases with increasing body mass and with male-biased sexual size dimorphism. However, we found no support for the predicted relationship between frequency and habitat. Our results suggest that the global variation in passerine song frequency is mostly driven by natural and sexual selection causing evolutionary shifts in body size rather than by habitat-related selection on sound propagation. Statement of authorshipTA and PM conceived and designed the study with input from all authors. TA and BK coordinated the study. PM collected the song data. MV performed the statistical analyses with input from WF. MB made the figures with help from MV and PM. TP and HB provided bioacoustic expertise. PM drafted the first version of the manuscript. TA, BK and PM revised and finalized the manuscript with input from all authors. Data availability statementThe data used in this study were collected from publicly available databases. All data and computer code used to generate the results, as well as supplementary figures and tables will be freely available at https://osf.io/fa9ky/.

evolutionary biology↗

bioRxiv2020

Body size and climate as predictors of plumage colouration and sexual dichromatism in parrots

Psittaciformes (parrots, cockatoos and lorikeets) comprise one of the most colourful clades of birds. Their unique pigments and cavity nesting habits are two potential explanations for their colourful character. However, plumage colour varies substantially between parrot species and sometimes also between males and females of the same species. Here, we use comparative analyses to evaluate what factors correlate with colour elaboration, colour diversity and sexual dichromatism. Specifically, we test the association between different aspects of parrot colouration and (1) the intensity of sexual selection and social interactions, (2) variation along the slow-fast life-history continuum and (3) climatic variation. We show that larger species and species that live in warm environments display more elaborated colours, yet smaller species have higher levels of sexual dichromatism. Larger parrots tend to have darker and more blue and red colours. Parrots that live in humid environments are darker and redder, whilst species inhabiting warm regions have more blue plumage colours. In general, the variables we considered explain small to moderate amounts of variation in parrot colouration (up to 20%). Our data suggest that sexual selection may be acting more strongly on males in small, short-lived parrots leading to sexual dichromatism. More elaborate colouration in both males and females of the larger, long-lived species with slow tropical life-histories suggests that mutual mate choice and reduced selection for crypsis may be important in these species, as has been shown for passerines.

evolutionary biology↗

bioRxiv2019

Timing of arrival in the breeding area is repeatable and affects reproductive success in a non-migratory population of blue tits

O_LIEvents in one part of the annual cycle often affect the performance (and subsequently fitness) of individuals later in the season (carry-over effects). An important aspect of this relates to the timing of activities. For example, many studies on migratory birds have shown that relatively late spring arrival in the breeding area reduces both the likelihood of getting a mate or territory and reproductive success.\nC_LIO_LIIn contrast, relatively little is known about movements of individuals in non-migratory populations during the non-breeding season. Few studies have investigated the timing of arrival at the breeding area in such species, possibly due to the assumption that most individuals remain in the area during the non-breeding season.\nC_LIO_LIIn this study, we used four years of data from a transponder-based automated recording system set up in a non-migratory population of blue tits (Cyanistes caeruleus) to describe individual variation in arrival at the breeding site. We investigated whether this variation can be explained by individual characteristics (sex, body size, or status), and we assessed its effect on aspects of reproductive success in the subsequent breeding season.\nC_LIO_LIWe found substantial variation in arrival date and demonstrate that this trait is individual-specific (repeatable). Females arrived later than males, but the arrival dates of social pair members were more similar than expected by chance. Arrival predicted both whether an individual would end up breeding that season, and several aspects of its breeding success.\nC_LIO_LIOur study suggests that non-migratory species show a form of incipient migration behaviour in that they leave the breeding area during the non-breeding season. We conclude that the timing of pre-breeding events, in particular arrival date, may be an overlooked, but important, fitness-relevant trait in non-migratory species.\nC_LI

animal behavior and cognition↗

bioRxiv2019

No evidence for disruption of global patterns of nest predation in shorebirds

Kubelka et al. (Science, 9 November 2018, p. 680-683) claim that climate change has disrupted patterns of nest predation in shorebirds. They report that predation rates have increased since the 1950s, especially in the Arctic. We describe methodological problems with their analyses and argue that there is no solid statistical support for their claims.

ecology↗

bioRxiv2018

RECONCILING ECOGEOGRAPHICAL RULES: RAINFALL AND TEMPERATURE PREDICT GLOBAL COLOUR VARIATION IN THE LARGEST BIRD RADIATION

Ecogeographical rules that associate climate with organismal form and function can reveal patterns of climatic adaptation. Two rules link animal coloration with climate: Glogers rule (darker coloration where wet and warm), and Bogerts rule (darker coloration where cold). Whereas Glogers rule was proposed for endotherms, and Bogerts rule for ectotherms, both rules may apply more broadly, despite their seemingly opposing effects. Here we test this contradiction on a global scale across passerine birds. Consistent with Glogers rule, birds were darker in wetter areas and, following Bogerts rule, lighter where warm, although birds became lighter again at very low temperatures. Rainfall and temperature had antagonistic or additive effects depending on their pattern of covariation, and this predicted whether birds followed the rules. We integrate both rules into a general framework to explain heterogeneity in climatic effects on coloration, which has implications to understand patterns of diversification, climatic adaptation and climate change impacts.

evolutionary biology↗

bioRxiv2017

Temporary mate removal during incubation leads to variable compensation in a biparental shorebir

Biparental care for offspring requires cooperation, but it is also a potential source of conflict, since one parent may care less at the expense of the other. How, then, do parents respond to the reduction of their partners care? Theoretical models predict that parents that feed offspring should partially compensate for the reduced care of their partner. However, for incubating birds partial compensation is unlikely the optimal strategy, because the entire brood can fail with reduced care. Although biparental incubation dominates in non-passerine birds, short-term manipulations of parental care and evaluations of individual differences in the response, both crucial to our understanding of parental cooperation, are scarce. Here, we describe the response of semipalmated sandpiper (Calidris pusilla) parents to a 24-hour removal of their partner during the incubation period, explore factors that can explain individual variation in the response, and describe how incubation rhythms changed after the removed parent returned. On average, the parents compensated partially for the absence of their partners care (59%; 95%CI: 49-70%, N = 25 individuals). The level of compensation did not differ between the sexes. However, individual responses varied from no to full compensation (2-101%). In seven nests where the removed parent never returned, the widowed parent attended the nest for 0-10 days (median: 4 days). In contrast to patterns observed in undisturbed nests or in uniparental species, nest attendance during compensation tended to be higher during the warmer part of the day. Although the level of compensation was not related to the before-experimental share of incubation, more responsive parents (that left the nest earlier upon human approach) compensated more. The quality of incubation in the after-experimental period was lower than usual, but improved quickly over time. Our findings suggest that full compensation might be limited by energetic constraints or by variation in responsiveness to the absence of the partner. Nevertheless, semipalmated sandpiper parents are able to adjust their subsequent incubation behaviour to take full responsibility for the nest when widowed. Because (nearly) full compensation was the most common response, we speculate that all individuals attempt full compensation, but that some fail because their energy stores get depleted, or because they are less responsive to the absence of their partner.

animal behavior and cognition↗

bioRxiv2016

Unexpected diversity in socially synchronized rhythms of shorebirds

The behavioural rhythms of organisms are thought to be under strong selection, influenced by the rhythmicity of the environment1-4. Such behavioural rhythms are well studied in isolated individuals under laboratory conditions1,5, but free-living individuals have to temporally synchronize their activities with those of others, including potential mates, competitors, prey and predators6-10. Individuals can temporally segregate their daily activities (e.g. prey avoiding predators, subordinates avoiding dominants) or synchronize their activities (e.g. group foraging, communal defence, pairs reproducing or caring for offspring)6-9,11. The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood5-7,9. Here, we address this in the context of biparental care, a particularly sensitive phase of social synchronization12 where pair members potentially compromise their individual rhythms. Using data from 729 nests of 91 populations of 32 biparentally-incubating shorebird species, where parents synchronize to achieve continuous coverage of developing eggs, we report remarkable within- and between-species diversity in incubation rhythms. Between species, the median length of one parents incubation bout varied from 1 - 19 hours, while period length-the time in which a parents probability to incubate cycles once between its highest and lowest value - varied from 6 - 43 hours. The length of incubation bouts was unrelated to variables reflecting energetic demands, but species relying on crypsis (the ability to avoid detection by other animals) had longer incubation bouts than those that are readily visible or actively protect their nest against predators. Rhythms entrainable to the 24-h light-dark cycle were less prevalent at high latitudes and absent in 18 species. Our results indicate that even under similar environmental conditions and despite 24-h environmental cues, social synchronization can generate far more diverse behavioural rhythms than expected from studies of individuals in captivity5-7,9. The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms.

animal behavior and cognition↗