Condition-dependent Signals Research Articles

IoT-interfaced solid-contact ion-selective electrodes for cyber-monitoring of element- specific nutrient information in hydroponics

This study aims to monitor element-specific nutrient information during hydroponic cultivation by IoT-interfaced miniaturized ion sensors. Because of size, cost, and manufacturing advantages, solid-contact ion-selective electrodes (SCISEs) were fabricated as an ion sensor array and interfaced with wireless embedded-systems to construct an IoT nutrient sensor system (IoNSS) for the first time. The entire IoNSS framework was composed of (i) a nutrient solution sampling and sensing module with SCISEs controlled by an Arduino Due® microcontroller, (ii) a Wio Terminal® microcontroller for automated procedure setting, data recording, and wireless transmission, (iii) a private cloud server (a Network Attached Storage equipped with Node-RED® and MongoDB®) for data management, and (iv) MQTT webpage-based interactive interfaces. In experiments, we found that potentiometric signal resolution and noise of the Arduino-interfaced SCISEs were significantly improved and approached to instrumental DAQ-like quality by additional delta-sigma ADC (ADS1115®) chip conditioning. This facilitated cost-effective harvest of precise and high-quality IoT ion sensor data. Before on-site applications, each SCISE was two-point calibrated in multiple-ion solutions and was checked with the fixed interference method. The ion concentration measurements were also compared with those of commercial ISEs and ion chromatography. To test the system’s feasibility, the IoNSS was applied to cyber-monitoring of K+, NO3–, and NH4+ concentrations during two-week hydroponic cultivation of arugula (E. vesicaria) in an indoor plant factory (in Northern Taiwan) with a modified Cornell solution and an outdoor greenhouse (in Southern Taiwan) with a modified Yamasaki solution, respectively. It was demonstrated that the IoNSS was capable of real-time observation of the crop’s nitrate/ammonium utilization and nutrient solution’s EC-element dependency. Besides, the web interfaces successfully reported growing condition-dependent ion signals in a simultaneous and remote manner. To sum up, this work achieves novel cybermonitoring of element-specific nutrients by IoT-interfaced SCISEs and paves a promising way for intelligent hydroponic management.

Carotenoid ornaments and the spandrels of physiology: a critique of theory to explain condition dependency.

Even as numerous studies have documented that the red and yellow coloration resulting from the deposition of carotenoids serves as an honest signal of condition, the evolution of condition dependency is contentious. The resource trade-off hypothesis proposes that condition-dependent honest signalling relies on a trade-off of resources between ornamental display and body maintenance. By this model, condition dependency can evolve through selection for a re-allocation of resources to promote ornament expression. By contrast, the index hypothesis proposes that selection focuses mate choice on carotenoid coloration that is inherently condition dependent because production of such coloration is inexorably tied to vital cellular processes. These hypotheses for the origins of condition dependency make strongly contrasting and testable predictions about ornamental traits. To assess these two models, we review the mechanisms of production of carotenoids, patterns of condition dependency involving different classes of carotenoids, and patterns of behavioural responses to carotenoid coloration. We review evidence that traits can be condition dependent without the influence of sexual selection and that novel traits can show condition-dependent expression as soon as they appear in a population, without the possibility of sexual selection. We conclude by highlighting new opportunities for studying condition-dependent signalling made possible by genetic manipulation and expression of ornamental traits in synthetic biological systems.

Not so monochromatic: Size-dependency of both sex and color in the cleaner wrasse Labroides dimidiatus

In marine interspecific cleaning mutualisms, small fish known as “cleaners” inspect the surface, gills and sometimes the mouth of “client” reef fish, eating ectoparasites, mucus, scales and dead or infected tissue. These cleaner fish species share similar vivid coloration that makes them recognizable by clients. To gain insight on additional communication roles of cleaner fish color, we tested if differences in color among cleaner wrasse Labroides dimidiatus individuals captured from the wild are explained by sex, body size or parasite loads. We found that males were larger, heavier and tended to have more saturated blue tails than females. We also found blue color saturation to be positively correlated with size, and that this size-dependence explains the trend for the sexes to differ in color. Parasite loads did not predict individual differences in color, but fish in our sample were not heavily parasitized. Other color traits (including yellow color saturation and black color brightness) did not differ between the sexes and were associated with morphological differences. Size-dependence of blue color may thus suggest that it is a condition-dependent signal that could be used in various types of inter- and intraspecific social interactions.

Offspring plumage coloration as a condition-dependent signal in the blue tit.

In many species, offspring display conspicuous coloration already early in life, even though they might be very vulnerable to predation at this stage. However, most attention has been drawn to the conspicuous plumage displayed by adult individuals in a sexual context, while other signaling functions have been explored much less. Here, we investigated whether the yellow breast plumage of blue tit (Cyanistes caeruleus) nestlings shows patterns of condition dependence and hence signals individual quality, as has been described for adult birds. During three consecutive breeding seasons, we, therefore, explored the association between nestling body mass and three color components of the yellow breast plumage (i.e., UV chroma, carotenoid chroma, and total brightness), considering both within and among nest effects. Variation in carotenoid chroma was not related to body mass. However, UV chroma and total brightness varied with body mass on an among-nest level, suggesting that they might signal aspects of genetic quality or parental rearing capacity. Interestingly, we also found a within-nest effect of body mass on total brightness, suggesting that this is a good candidate for a condition-dependent signal within the family. Thus, other family members could rely on brightness to adjust their behavioral strategies, such as feeding behavior in parents. Our study thus reveals that certain color components of the yellow breast plumage might signal different aspects of offspring quality, and they might have a correlated signaling value across life-history stages.

Effects of genetic vs. environmental quality on condition-dependent morphological and life history traits in a neriid fly.

Condition is assumed to reflect both genes and environment, enabling condition‐dependent signals to reveal genetic quality. However, because the phenotypic effects of variation in genetic quality could be masked by environmental heterogeneity, the contribution of genetic quality to phenotypic variation in fitness‐related traits and condition‐dependent signals remains unclear. We compared effects of ecologically relevant manipulations of environmental quality (nutrient dilution in the larval diet) and genetic quality (one generation of inbreeding) on male and female morphology, life history and reproductive performance in the neriid fly Telostylinus angusticollis. We found that larval diet quality had strong, positive effects on male and female body size, male secondary sexual traits, and aspects of male and female reproductive performance. By contrast, inbreeding had weak effects on most traits, and no trait showed clear and consistent effects of both environmental and genetic quality. Indeed, inbreeding effects on body size and male competitive performance were of opposite sign in rich vs. poor larval diet treatment groups. Our results suggest that environmental quality strongly affects condition, but the effects of genetic quality are subtle and environment‐dependent in this species. These findings raise questions about the genetic architecture of condition and the potential for condition‐dependent traits to function as signals of genetic quality.

Fitness Costs of Maternal Ornaments and Prenatal Corticosterone Manifest as Reduced Offspring Survival and Sexual Ornament Expression.

Colorful traits (i.e., ornaments) that signal quality have well-established relationships with individual condition and physiology. Furthermore, ornaments expressed in females may have indirect fitness effects in offspring via the prenatal physiology associated with, and social consequences of, these signaling traits. Here we examine the influence of prenatal maternal physiology and phenotype on condition-dependent signals of their offspring in adulthood. Specifically, we explore how prenatal maternal testosterone, corticosterone, and ornament color and size correlate with female and male offspring survival to adulthood and ornament quality in the lizard Sceloporus undulatus. Offspring of females with more saturated badges and high prenatal corticosterone were less likely to survive to maturity. Badge saturation and area were negatively correlated between mothers and their male offspring, and uncorrelated to those in female offspring. Maternal prenatal corticosterone was correlated negatively with badge saturation of male offspring in adulthood. Our results indicate that maternal ornamentation and prenatal concentrations of a stress-relevant hormone can lead to compounding fitness costs by reducing offspring survival to maturity and impairing expression of a signal of quality in surviving males. This mechanism may occur in concert with social costs of ornamentation in mothers. Intergenerational effects of female ornamentation and prenatal stress may be interdependent drivers of balancing selection and intralocus sexual conflict over signaling traits.

How urbanization affects sexual communication.

Urbanization is rapidly altering landscapes worldwide, changing environmental conditions, and creating novel selection pressures for many organisms. Local environmental conditions affect the expression and evolution of sexual signals and mating behaviors; changes in such traits have important evolutionary consequences because of their effect on reproduction. In this review, we synthesize research investigating how sexual communication is affected by the environmental changes associated with urbanization—including pollution from noise, light, and heavy metals, habitat fragmentation, impervious surfaces, urban heat islands, and changes in resources and predation. Urbanization often has negative effects on sexual communication through signal masking, altering condition‐dependent signal expression, and weakening female preferences. Though there are documented instances of seemingly adaptive shifts in trait expression, the ultimate impact on fitness is rarely tested. The field of urban evolution is still relatively young, and most work has tested whether differences occur in response to various aspects of urbanization. There is limited information available about whether these responses represent phenotypic plasticity or genetic changes, and the extent to which observed shifts in sexual communication affect reproductive fitness. Our understanding of how sexual selection operates in novel, urbanized environments would be bolstered by more studies that perform common garden studies and reciprocal transplants, and that simultaneously evaluate multiple environmental factors to tease out causal drivers of observed phenotypic shifts. Urbanization provides a unique testing ground for evolutionary biologists to study the interplay between ecology and sexual selection, and we suggest that more researchers take advantage of these natural experiments. Furthermore, understanding how sexual communication and mating systems differ between cities and rural areas can offer insights on how to mitigate negative, and accentuate positive, consequences of urban expansion on the biota, and provide new opportunities to underscore the relevance of evolutionary biology in the Anthropocene.

Colourful traits in female birds relate to individual condition, reproductive performance and male-mate preferences: a meta-analytic approach.

Colourful traits in females are suggested to have evolved and be maintained by sexual selection. Although several studies have evaluated this idea, support is still equivocal. Evidence has been compiled in reviews, and a handful of quantitative syntheses has explored cumulative support for the link between condition and specific colour traits in males and females. However, understanding the potential function of females' colourful traits in sexual communication has not been the primary focus of any of those previous studies. Here, using a meta-analytic approach, we find that evidence from empirical studies in birds supports the idea that colourful female ornaments are positively associated with residual mass and immune response, clutch size and male-mate preferences. Hence, colourful traits in female birds likely evolved and are maintained by sexual selection as condition-dependent signals.

Like Father Like Son: Cultural and Genetic Contributions to Song Inheritance in an Estrildid Finch.

Social learning of vocalizations is integral to song inheritance in oscine passerines. However, other factors, such as genetic inheritance and the developmental environment, can also influence song phenotype. The relative contributions of these factors can have a strong influence on song evolution and may affect important evolutionary processes such as speciation. However, relative contributions are well-described only for a few species and are likely to vary with taxonomy. Using archived song data, we examined patterns of song inheritance in a domestic population of Java sparrows (Lonchura oryzivora), some of which had been cross-fostered. Six-hundred and seventy-six songs from 73 birds were segmented and classified into notes and note subtypes (N = 22,972), for which a range of acoustic features were measured. Overall, we found strong evidence for cultural inheritance of song structure and of the acoustic characteristics of notes; sons’ song syntax and note composition were similar to that of their social fathers and were not influenced by genetic relatedness. For vocal consistency of note subtypes, a measure of vocal performance, there was no apparent evidence of social or genetic inheritance, but both age and developmental environment influenced consistency. These findings suggest that high learning fidelity of song material, i.e., song structure and note characteristics, could allow novel variants to be preserved and accumulate over generations, with implications for evolution and conservation. However, differences in vocal performance do not show strong links to cultural inheritance, instead potentially serving as condition dependent signals.

A condition-dependent male sexual signal predicts adaptive predator-induced plasticity in offspring

The possibility that sexual selection promotes adaptive evolution in variable environments remains controversial. In particular, where the scale of environmental variation results in parents and their offspring experiencing different environmental conditions, such variation is expected to break down associations between adult sexual traits and adaptive offspring traits. However, when adaptive offspring plasticity in nonsexual traits acts as an indirect benefit of mate choice, then mate choice for males that produce more plastic offspring could promote adaptation to variable environments. This hypothesis assumes that male sexual signals predict offspring plasticity, which has rarely been tested. To test this assumption, we used spadefoot toads (Spea multiplicata) to investigate whether variation in male sexual signals predicts the expression of tadpole tail-fin plasticity in response to predation cues. Such plasticity has been shown to be adaptive in numerous amphibian taxa. We found that condition-dependent male call characteristics predicted offspring plasticity. Generally, both phenotypic plasticity and female mate choice are ubiquitous in nature; therefore, adaptive associations between male sexual signals and offspring plasticity such as the one reported here might be common. Sexual signals can indicate individuals’ capacity to sire high-quality offspring, which provides a mechanism by which sexual selection can contribute to adaptive evolution. Whether this occurs in variable environments is unclear, however, because variable environments can expose parents and their offspring to different selection pressures. To address this uncertainty, we investigated the possibility that sexual signals can signal the capacity to sire offspring that express adaptive phenotypic plasticity in response to prevailing selective pressures. Using spadefoot toads, we found that condition-dependent male sexual signals predict the expression of tadpole tail-fin plasticity in response to predation cues. Because this form of plasticity has been demonstrated to be adaptive in several amphibian taxa, our results suggest that associations between sexual signals and adaptive offspring plasticity can allow sexual selection to promote adaptive evolution in variable environments.

Condition-dependent differences in male vibratory pre-copulatory and copulatory courtship in a nuptial gift-giving spider

Condition-dependent secondary sexual traits and signals are often crucial for mate choice decisions. Nuptial gifts, provided by the male to the female during mating, may represent an indicator of male condition, especially if production of the gift is energetically costly. Additionally, other signalling modalities may well play a role in mate choice in such systems. Females of the nursery web spider Pisaura mirabilis preferably mate with males that provide a prey item wrapped in silk. Apart from the nuptial gift, vibrational signals employed during courtship and mating may reveal additional information about male condition. We tested condition-dependence of male vibrational signals of well-fed versus starved males, when in contact with female dragline silk and during mating trials. Our results show that vibrational signals are produced in P. mirabilis, both during pre-copulatory courtship and during copulation. Male courtship signals were condition-dependent: males in good condition initiated signalling earlier and emitted more vibrational pulses than poor-condition males. They were also more likely to be accepted by the female for copulation. We additionally identified vibrational signals during copulation. These signals were different from pre-copulatory courtship vibrations but did not differ between the treatment groups. This study shows that vibrational communication plays an important role before and during copulation in P. mirabilis. It sets the stage for further experiments on spider biotremology associated with nuptial gift giving behaviour.Significance statementMale courtship behaviour can indicate a male’s condition and quality and be subject to female mate choice. Vibrational communication during mating plays a crucial role in many animal species. Spiders are known to be extremely sensitive towards vibrations, and there is evidence that vibratory signals are also used during courtship. Here, we study the nuptial gift-giving spider Pisaura mirabilis in which courtship entails providing a nuptial gift by the male to the female. The gift quality determines on the probability and duration of mating. We investigated the role of vibrational behaviour in this species by standardizing nuptial gifts. Our study demonstrates that vibratory signals comprise information about the male’s condition, that signals are also produced during mating and that courtship and copulatory signals are strikingly different. We suggest that vibrational communication provides important condition-dependent traits for female mate choice in addition to the nuptial gift.

The role of oxidative stress in postcopulatory selection.

Two decades ago, von Schantz et al. (von Schantz T, Bensch S, Grahn M, Hasselquist D, Wittzell H. 1999 Good genes, oxidative stress and condition-dependent sexual signals. Proc. R. Soc. B 266, 1-12. (doi:10.1098/rspb.1999.0597)) united oxidative stress (OS) biology with sexual selection and life-history theory. This set the scene for analysis of how evolutionary trade-offs may be mediated by the increase in reactive molecules resulting from metabolic processes at reproduction. Despite 30 years of research on OS effects on infertility in humans, one research area that has been left behind in this integration of evolution and OS biology is postcopulatory sexual selection-this integration is long overdue. We review the basic mechanisms in OS biology, why mitochondria are the primary source of ROS and ATP production during oxidative metabolism, and why sperm, and its performance, is uniquely susceptible to OS. We also review how postcopulatory processes select for antioxidation in seminal fluids to counter OS and the implications of the net outcome of these processes on sperm damage, sperm storage, and female and oocyte manipulation of sperm metabolism and repair of DNA to enhance offspring fitness. This article is part of the theme issue 'Fifty years of sperm competition'.

Sex-specific relationships between urbanization, parasitism, and plumage coloration in house finches

Abstract Historically, studies of condition-dependent signals in animals have been male-centric, but recent work suggests that female ornaments can also communicate individual quality (e.g., disease state, fecundity). There also has been a surge of interest in how urbanization alters signaling traits, but we know little about if and how cities affect signal expression in female animals. We measured carotenoid-based plumage coloration and coccidian (Isospora spp.) parasite burden in desert and city populations of house finches Haemorhous mexicanus to examine links between urbanization, health state, and feather pigmentation in males and females. In earlier work, we showed that male house finches are less colorful and more parasitized in the city, and we again detected such patterns in this study for males; however, urban females were less colorful, but not more parasitized, than rural females. Moreover, contrary to rural populations, we found that urban birds (regardless of sex) with larger patches of carotenoid coloration were also more heavily infected with coccidia. These results show that urban environments can disrupt condition-dependent color expression and highlight the need for more studies on how cities affect disease and signaling traits in both male and female animals.

Cleaner blues: Condition-dependent colour and cleaner fish service quality

While vivid colours in sexual signals can provide information on individual quality, vivid colours in interspecific signals have been interpreted mostly as indicating species identity and maximizing signal detection. Here we investigate if colour differences in an interspecific signal could also indicate relevant aspects of individual quality because, similarly to sexual signalling, in interspecific communication it could sometimes be advantageous to assess individual quality. For example when interacting with cleaner species, clients should benefit from assessing which individual cleaners provide better service. Since oxidative stress commonly influence condition-dependent colour signals, we oxidized the diet of cleaner wrasses (Labroides dimidiatus) in laboratory conditions to test if this affects their vivid blue skin colour and the quality of their cleaning service. Compared to controls, experimental cleaners decreased blue colour saturation after the oxidized diet treatment, decreased the quality of their cleaning service by performing less tactile stimulation and, although clients in the laboratory were de-parasitized, also tended to decrease the touching the client with the mouth. We used visual modelling, based on the spectral sensitivity of vision in various client species, to show that some client species can perceive these changes in cleaner blue colour saturation, while other client species not. We suggest that, similarly to sexual signals, some vivid colours used in interspecific communication may convey information on aspects of individual quality that are relevant to heterospecifics.

Design, delivery and perception of condition-dependent chemical signals in strepsirrhine primates: implications for human olfactory communication.

The study of human chemical communication benefits from comparative perspectives that relate humans, conceptually and empirically, to other primates. All major primate groups rely on intraspecific chemosignals, but strepsirrhines present the greatest diversity and specialization, providing a rich framework for examining design, delivery and perception. Strepsirrhines actively scent mark, possess a functional vomeronasal organ, investigate scents via olfactory and gustatory means, and are exquisitely sensitive to chemically encoded messages. Variation in delivery, scent mixing and multimodality alters signal detection, longevity and intended audience. Based on an integrative, 19-species review, the main scent source used (excretory versus glandular) differentiates nocturnal from diurnal or cathemeral species, reflecting differing socioecological demands and evolutionary trajectories. Condition-dependent signals reflect immutable (species, sex, identity, genetic diversity, immunity and kinship) and transient (health, social status, reproductive state and breeding history) traits, consistent with socio-reproductive functions. Sex reversals in glandular elaboration, marking rates or chemical richness in female-dominant species implicate sexual selection of olfactory ornaments in both sexes. Whereas some compounds may be endogenously produced and modified (e.g. via hormones), microbial analyses of different odorants support the fermentation hypothesis of bacterial contribution. The intimate contexts of information transfer and varied functions provide important parallels applicable to olfactory communication in humans. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Full spectra coloration and condition-dependent signaling in a skin-based carotenoid sexual ornament

AbstractCarotenoid-based traits commonly act as condition-dependent signals of quality to both males and females. Such colors are typically quantified using summary metrics (e.g., redness) derived by partitioning measured reflectance spectra into blocks. However, perceived coloration is a product of the whole spectrum. Recently, new methods have quantified a range of environmental factors and their impact on reflection data at narrow wavebands across the whole spectrum. Using this approach, we modeled the reflectance of red integumentary eye combs displayed by male black grouse (Lyrurus tetrix) as a function of ornament size and variables related to male quality. We investigated the strength and direction of effect sizes of variables at each waveband. The strongest effect on the spectra came from eye comb size, with a negative effect in the red part of the spectrum and a positive effect in ultraviolet reflectance. Plasma carotenoid concentration and body mass were also related to reflectance variance in differing directions across the entire spectra. Comparisons of yearlings and adults showed that the effects were similar but stronger on adult reflectance spectra. These findings suggest that reflectance in different parts of the spectrum is indicative of differing components of quality. This method also allows a more accurate understanding of how biologically relevant variables may interact to produce perceived coloration and multicomponent signals and where the strongest biological effects are found.

Male preferences for nuptial gifts and gift weight loss amongst the nursery web spider, Pisaura mirabilis

Sexual signals produced by males are costly. Thus, sexual selection may favour males who are able to minimise these costs, but are still reproductively successful. I investigated male preferences for large and small prey used to produce nuptial gifts, which serve as sexual signals in the nursery web spider, Pisaura mirabilis. Males showed strong preferences for large prey compared to small prey for gift production, which is likely to be more attractive for females and provide males with longer copulation. These preferences were strongest in the presence of female pheromonal cues. Unexpectedly, carrying nuptial gifts did not influence male mobility measured in a 5-min-long behavioural test. Both gifts carried by males and the intact gifts showed similar decreases in mass, suggesting that males did not actively suck the content of the gift. Wrapping the gift with silk did not effectively reduce the gift’s dehydration, meaning that the function of the silk is not to protect the gift’s contents. Males in poor body condition were more likely to feed on the prey before wrapping it. This is consistent with condition dependent signalling, as males in low condition are predicted to feed on the prey as they are not able to pay the cost of gift production. Males preferred large-sized prey for gift production and males in poor body condition reduced the cost of gift production by feeding on the prey, supporting the idea that nuptial feeding is condition dependent.

Ornaments and condition: plumage patch sizes, nutritional reserve state, reserve accumulation, and reserve depletion

Condition-dependence is considered as a dominant mechanism ensuring the fitness benefits of continued mate choice for heritable sexual signal traits, but crucial questions remain concerning the underlying physiological pathways. For example, it is unclear whether condition-dependence is mediated by the different amount of resource obtained, some uncheatable functional link with nutritional status, or the adverse effect of nutritional stress experienced by some individuals. Furthermore, the pattern of change in nutritional reserves in relation to ornamental traits has recently been proposed as a critical pillar of the condition-dependence concept, but this pattern is virtually unknown in natural populations. We quantified separate measures for actual body condition, lipid reserve accumulation rate, and lipid reserve depletion, and applied these measures to two white plumage ornaments of male collared flycatchers during courtship, during nestling rearing, and before the summer moult. Neither actual condition nor reserve accumulation rate before moult predicted the subsequent change of ornament sizes, but reserve depletion was accompanied by the reduction of forehead patch size to the following year. Wing patch size, a trait important in territoriality, was negatively related to both reserve accumulation and reserve depletion in the courtship period, but not related to current condition. Finally, irrespective of breeding phase, measures of current condition, and recent nutritional reserve depletion were negatively correlated, but both were unrelated to resource accumulation rate. These results indicate that measuring nutritional reserve trajectories in addition to actual condition may reveal functionally important processes underlying signal-condition correlations.Significance statementOrnamental signal characters are known to convey honest information to signal receivers through their dependence on nutritional condition. Here, we show that such signals can also indicate the temporal trends of condition. We examine plumage patch sizes and separate measures of actual condition, nutritional reserve accumulation, and nutritional reserve depletion in three contexts: during courtship, during nestling rearing, and before the summer moult. The results suggest nutritional stress effects on signal expression, and predictable reserve dynamics in relation to signal expression, thereby highlighting the usefulness of dynamic nutritional measures in clarifying the fundamental concept of condition-dependent signalling.

Condition-Dependent Begging Elicits Increased Parental Investment in a Wild Bird Population.

The coevolution of parental supply and offspring demand has long been thought to involve offspring need driving begging and parental care, leaving other hypotheses underexplored. In a population of wild birds, we experimentally tested whether begging serves as a negatively condition-dependent signal of need or a positively condition-dependent signal of quality. Across multiple years, we supplemented nestling house wrens with food shortly after hatching and simultaneously manipulated corticosterone levels to simulate the hunger-induced increase in glucocorticoids thought to mediate begging. This allowed us to also test whether begging is simply a proximate signal of hunger. Days after supplementation ended, food-supplemented nestlings were in better condition than nonsupplemented nestlings and begged for food at an increased rate; their parents, in turn, increased provisioning to a greater extent than parents of nonsupplemented young, as begging positively predicted provisioning. Food-supplemented nestlings therefore attained above-average condition, which predicted their recruitment as breeding adults in the local population. Glucocorticoids increased begging in the short term, but this transient effect depended on satiety. Thus, glucocorticoids promoted begging as a proximate response to hunger, whereas the longer-term changes in nestling condition, begging, and food provisioning suggest that begging ultimately signals offspring quality to elicit increased investment, thereby enhancing offspring survival.

Use of plumage and gular pouch color to evaluate condition of oil spill rehabilitated California brown pelicans (Pelecanus occidentalis californicus) post-release.

Sublethal effects of oil spills may dampen seabird rehabilitation success due to lingering negative impacts of contamination and stress on reproduction and long-term survival. These effects can be difficult to measure while birds are in care as well as once birds are released. Expression of sexually selected traits that are sensitive to condition can provide information on physiological status of birds. We evaluated plumage molt and gular pouch skin color of California brown pelicans (Pelecanus occidentalis californicus) following oil contamination and rehabilitation to test for differences between previously oiled and rehabilitated (post-spill) and presumably uncontaminated pelicans. Post-spill pelicans released with either color leg bands alone, or bands plus harness-mounted satellite GPS tags, were relocated and visually assessed in the field at non-breeding communal roosts and compared to surrounding unmarked pelicans in the general population. Non-oiled pelicans bearing GPS tags were also included in the study. Post-spill pelicans lagged the general population in molt of ornamental yellow crown feathers but hind neck transition into white plumage was not significantly different. Both post-spill and non-oiled pelicans wearing GPS tags had lower gular redness scores than the unmarked, non-oiled population. Pre-breeding gular pouch redness of post-spill pelicans was more strongly influenced by wearing of a GPS tag than a history of oil contamination and rehabilitation. Gular pouch redness of post-spill pelicans in the first 18 months after release was positively correlated with long term survivorship. If gular pouch color is a condition-dependent sexual signal and overall health influences plumage molt progression, our results indicate that many post-spill pelicans marked with bands alone were in relatively good condition going into the next breeding season, but those released with electronic tags experienced additional stress due to wearing the equipment, introducing a confounding variable to the post-release study.