Max Planck Institute for Ornithology

A major barrier to advancing ornithology is the systemic exclusion of professionals from the Global South. A recent special feature, Advances in Neotropical Ornithology, and a shortfalls analysis therein, unintentionally followed a long-standing pattern of highlighting individuals, knowledge, and views from the Global North, while largely omitting the perspectives of people based within the Neotropics. Here, we review current strengths and opportunities in the practice of Neotropical ornithology. Further, we discuss problems with assessing the state of Neotropical ornithology through a northern lens, including discovery narratives, incomplete (and biased) understanding of history and advances, and the promotion of agendas that, while currently popular in the north, may not fit the needs and realities of Neotropical research. We argue that future advances in Neotropical ornithology will critically depend on identifying and addressing the systemic barriers that hold back ornithologists who live and work in the Neotropics: unreliable and limited funding, exclusion from international research leadership, restricted dissemination of knowledge (e.g., through language hegemony and citation bias), and logistical barriers. Moving forward, we must examine and acknowledge the colonial roots of our discipline, and explicitly promote anti-colonial agendas for research, training, and conservation. We invite our colleagues within and beyond the Neotropics to join us in creating new models of governance that establish research priorities with vigorous participation of ornithologists and communities within the Neotropical region. To include a diversity of perspectives, we must systemically address discrimination and bias rooted in the socioeconomic class system, anti-Blackness, anti-Brownness, anti-Indigeneity, misogyny, homophobia, tokenism, and ableism. Instead of seeking individual excellence and rewarding top-down leadership, institutions in the North and South can promote collective leadership. In adopting these approaches, we, ornithologists, will join a community of researchers across academia building new paradigms that can reconcile our relationships and transform science. Spanish and Portuguese translations are available in the Supplementary Material.

The categorization of animal vocalizations into distinct behaviorally relevant groups for communication is an essential operation that must be performed by the auditory system. This auditory object recognition is a difficult task that requires selectivity to the group identifying acoustic features and invariance to renditions within each group. We find that small ensembles of auditory neurons in the forebrain of a social songbird can code the bird's entire vocal repertoire (∼10 call types). Ensemble neural discrimination is not, however, correlated with single unit selectivity, but instead with how well the joint single unit tunings to characteristic spectro-temporal modulations span the acoustic subspace optimized for the discrimination of call types. Thus, akin to face recognition in the visual system, call type recognition in the auditory system is based on a sparse code representing a small number of high-level features and not on highly selective grandmother neurons.

Reproductive phenotypes are shaped by genetic, physiological and environmental variation that an organism experiences during ontogeny. Steroid hormones play an integrative role in this process through both genomic and non-genomic pathways. Differences in steroid hormone metabolism may be rooted in genomic variation. Here we evaluate the influence of supergene variants underlying alternative reproductive tactics on sex steroid metabolism during ontogeny in ruffs (Calidris pugnax). Adult ruff males exhibit three male mating morphs called Independents, Faeders and Satellites, that differ prominently in circulating androgen (testosterone and androstenedione) concentrations. Across morphs and sexes chicks showed similar mean androgen concentrations during ontogenetic development. However, variances in circulating androgens showed the same pattern as corresponding variances previously observed in adults. HSD17B2 had been previously identified as a key gene for mediating differences in androgen levels between morphs as it encodes the enzyme that converts testosterone to androstenedione and is located within the supergene. Observed HSD17B2 expression in embryonic brain tissue was consistent with predictions based on genetic and endocrine differences. Taken together, the observed differences in circulating androgen concentrations and gene expression point to testosterone synthesis as a key mechanism that shapes developmental trajectories and differences in brain organization among morphs.

In 2020, the COVID-19 pandemic led to a reduction in human activities and restriction of all but essential movement for much of the world's population. A large, but temporary, increase in air and water quality followed, and there have been several reports of animal populations moving into new areas. Extending on long-term monitoring efforts, we examined how coral reef fish populations were affected by the government-mandated lockdown across a series of Marine Protected Area (MPA) and non-Marine Protected Area (nMPA) sites around Moorea, French Polynesia. During the first six-week lockdown that Moorea experienced between March and May 2020, increases (approx. two-fold) in both harvested and non-harvested fishes were observed across the MPA and nMPA inner barrier reef sites, while no differences were observed across the outer barrier sites. Interviews with local amateur and professional fishers indicated that while rules regarding MPA boundaries were generally followed, some subsistence fishing continued in spite of the lockdown, including within MPAs. As most recreational activities occur along the inner reef, our data suggest that the lockdown-induced reduction in recreational activities resulted in the recolonization of these areas by fishes, highlighting how fish behaviour and space use can rapidly change in our absence.

Fluctuations in environmental temperature affect energy metabolism and stimulate the expression of reversible phenotypic plasticity in vertebrate behavioural and physiological traits. Changes in circulating concentrations of glucocorticoid hormones often underpin environmentally induced phenotypic plasticity. Ongoing climate change is predicted to increase fluctuations in environmental temperature globally, making it imperative to determine the standing phenotypic variation in glucocorticoid responses of free-living populations to evaluate their potential for coping via plastic or evolutionary changes. Using a reaction norm approach, we repeatedly sampled wild great tit ( Parus major ) individuals for circulating glucocorticoid concentrations during reproduction across five years to quantify individual variation in glucocorticoid plasticity along an environmental temperature gradient. As expected, baseline and stress-induced glucocorticoid concentrations increased with lower environmental temperatures at the population and within-individual level. Moreover, we provide unique evidence that individuals differ significantly in their plastic responses to the temperature gradient for both glucocorticoid traits, with some displaying greater plasticity than others. Average concentrations and degree of plasticity covaried for baseline glucocorticoids, indicating that these two reaction norm components are linked. Hence, individual variation in glucocorticoid plasticity in response to a key environmental factor exists in a wild vertebrate population, representing a crucial step to assess their potential to endure temperature fluctuations.

High numbers of harbor porpoises (Phocoena phocoena) end up as bycatch in gillnets every year. Acoustic alarms (pingers) have been demonstrated to be an efficient mitigation tool to prevent bycatch of this species; however, little is known about the behavioral reactions of wild porpoises to pingers. This knowledge is important for optimizing the design and use of pingers. We tracked 16 wild porpoises with a drone and recorded their behavior before and during exposure to pinger sounds. Range from the pinger to the porpoise was 158–797 m when the pinger was first activated. In four of the exposures, with pinger-to-porpoise ranges of 199–521 m, reaction to the pinger was strong avoidance behavior with increased swimming speed heading away from the pinger. Average number of surfacings decreased from 3.4 surfacings/min before pinging to 2.8 surfacings/min during pinging. Eight animals were lost from the drone’s field of view as soon as the pinger playback started, indicating that they were either diving deep or speeding away from the area very rapidly. Four animals did not respond to pinger sounds, demonstrating a diversity in the behavioral response. Neither the behavior of porpoises (i.e., foraging, socializing and traveling) before sound exposure, the animal’s initial direction in relation to the sound source, nor the porpoise-to-pinger range affected their reaction in relation to the pinger. Pingers can cause very strong aversive reactions in harbor porpoises, which explains their efficiency in reducing bycatch. The strong aversive reactions may suggest that pinger use should be limited to critical time periods and regions, or that more focus needs to be put on developing acoustic devices which cause less severe behavioral reactions. At the same time, this study shows that 25 % of animals may not react to pinger sounds, indicating a great diversity in behavioral responses.

Understanding the characteristics of a species’s distribution represents a challenge in marine environments because movement patterns and foraging areas are restricted by highly dynamic spatiotemporal variations in environmental conditions. In response to this heterogeneous context, marine predators such as seabirds need to maximize their foraging efficiency, especially during the breeding season, when movement is restricted by the need to return to the nest. Biologging technologies such as satellite transmitters and Global Positioning System (GPS) receivers allow researchers to track birds at sea and investigate the relationship between foraging strategy and changing oceanographic features. Our study focuses on characterizing the feeding areas of Magnificent Frigatebird (Fregata magnificens) breeding in Baja California Sur, Mexico. We used GPS receivers to track the foraging flights of frigatebirds during 2017–2019, identifying the core foraging areas and characterizing environmental conditions and marine productivity in these areas. Individuals repeatedly selected areas close to the colonies located in Espíritu Santo archipelago (Gulf of California) and Santa Margarita Island (Pacific Ocean). However, some males flew to more distant and equally productive areas to the south and north of the Baja California peninsula. We presume that the differential use of foraging areas between males and females reflects biometrical and behavioral differences of the sexes, which may explain the relationships between foraging behavior and breeding, intraspecific competition, and sex-based differences in parental investment. Because frigatebirds are considered indicators of marine environmental conditions, our data are useful to identify areas where prey species aggregate in space and time and, therefore, to expand the boundaries of existing marine protected areas. Data on seabird foraging ranges described here can be useful for delineating marine protected area boundaries and can be considered suitable candidates for inclusion in appropriately designated regional marine spatial planning.

Experimental manipulations of testosterone have advanced our understanding of the hormonal control of traits across vertebrates. Implants are commonly used to supplement testosterone and other hormones to organisms, as they can be readily scaled to produce desired hormone levels in circulation. Concerns about pharmacological (i.e. unnatural) doses of traditional silastic implants led to innovation in implant methods, with time-release pellets and beeswax implants proposed as solutions. A study comparing silastic, time-release pellets, and beeswax implants found the latter to be most effective in delivering a physiologically relevant dose. One proposed advantage to subcutaneous beeswax implants is that they are expected to degrade within the body, thus removing the obligation to recapture implanted individuals in the field. However, few studies have reported on dosage and no published literature has examined the assumption that beeswax implants readily degrade as expected. Here we present time-release androgen data in relation to implants containing varying levels of testosterone from four separate implant studies. In addition, we report long-term persistence of subcutaneous implants, including two cases of implants being retained for > 2 years. Finally, we offer recommendations on the composition and implementation of beeswax implants to aid the pursuit of minimally invasive and physiologically relevant manipulations of circulating hormones.

Female ornaments are often reduced, male-like traits. Although these were long perceived as non-functional, it is now broadly accepted that female ornaments can be adaptive. However, it is unclear whether this is as common in females as it is in males, and whether ornaments fulfil similar signalling roles. Here, we apply a bivariate meta-analysis to a large dataset of ornaments in mutually ornamented birds. As expected, female ornament expression tends to be reduced compared to males. However, ornaments are equally strongly associated with indicators of condition and aspects of reproductive success in both sexes, regardless of the degree of sexual dimorphism. Thus, we show here in a paired comparison within-and-across species, that ornaments in birds provide similar information in both sexes: more ornamented individuals are in better condition and achieve higher reproductive success. Although limited by their correlational nature, these outcomes imply that female ornaments could widely function in a similar manner as male ornaments.

The superior colliculus is a midbrain structure that plays important roles in visually guided behaviors in mammals. Neurons in the superior colliculus receive inputs from retinal ganglion cells but how these inputs are integrated in vivo is unknown. Here, we discovered that high-density electrodes simultaneously capture the activity of retinal axons and their postsynaptic target neurons in the superior colliculus, in vivo. We show that retinal ganglion cell axons in the mouse provide a single cell precise representation of the retina as input to superior colliculus. This isomorphic mapping builds the scaffold for precise retinotopic wiring and functionally specific connection strength. Our methods are broadly applicable, which we demonstrate by recording retinal inputs in the optic tectum in zebra finches. We find common wiring rules in mice and zebra finches that provide a precise representation of the visual world encoded in retinal ganglion cells connections to neurons in retinorecipient areas.

The Massim, a cultural region that includes the southeastern tip of mainland Papua New Guinea (PNG) and nearby PNG offshore islands, is renowned for a trading network called Kula, in which different valuable items circulate in different directions among some of the islands. While the Massim has been a focus of anthropological investigation since the pioneering work of Malinowski in 1922, the genetic background of its inhabitants remains relatively unexplored. To characterize the Massim genomically, we generated genome-wide SNP data from 192 individuals from 15 groups spanning the entire region. Analyzing these together with comparative data, we found that all Massim individuals have variable Papuan-related (indigenous) and Austronesian-related (arriving ∼3,000 years ago) ancestries. Individuals from Rossel Island in southern Massim, speaking an isolate Papuan language, have the highest amount of a distinct Papuan ancestry. We also investigated the recent contact via sharing of identical by descent (IBD) genomic segments and found that Austronesian-related IBD tracts are widely distributed geographically, but Papuan-related tracts are shared exclusively between the PNG mainland and Massim, and between the Bismarck and Solomon Archipelagoes. Moreover, the Kula-practicing groups of the Massim show higher IBD sharing among themselves than do groups that do not participate in Kula. This higher sharing predates the formation of Kula, suggesting that extensive contact between these groups since the Austronesian settlement may have facilitated the formation of Kula. Our study provides the first comprehensive genome-wide assessment of Massim inhabitants and new insights into the fascinating Kula system.

The relationships between avian brood parasites and their hosts are widely recognised as model systems for studying coevolution. However, while most brood parasites are known to parasitise multiple species of host and hosts are often subject to parasitism by multiple brood parasite species, the examination of multispecies interactions remains rare. Here, we compile data on all known brood parasite–host relationships and find that complex brood parasite–host systems, where multiple species of brood parasites and hosts coexist and interact, are globally commonplace. By examining patterns of past research, we outline the disparity between patterns of network complexity and past research emphases and discuss factors that may be associated with these patterns. Drawing on insights gained from other systems that have embraced a multispecies framework, we highlight the potential benefits of considering brood parasite–host interactions as ecological networks and brood parasitism as a model system for studying multispecies interactions. Overall, our results provide new insights into the diversity of these relationships, highlight the stark mismatch between past research efforts and global patterns of network complexity, and draw attention to the opportunities that more complex arrangements offer for examining how species interactions shape global patterns of biodiversity.

Quantifying stress and energetic responses in animals is a major challenge as existing methods lack temporal resolution and elevate animal stress. We propose “wake respirometry”, a new method of quantifying fine-scale changes in CO2 production in unrestrained animals, using a non-dispersive infrared CO2 sensor positioned downwind of the animal i.e. in its wake. We parameterise the dispersion of CO2 in wakes using known CO2 flow rates and wind speeds. Tests with three bird species in a wind tunnel demonstrated that the system can resolve breath-by-breath changes in CO2 concentration, with clear exhalation signatures increasing in period and integral with body size. Changes in physiological state were detectable following handling, flight and exposure to a perceived threat. We discuss the potential of wake respirometry to quantify stress and respiratory patterns in wild animals and provide suggestions for estimating behaviour-specific metabolic rates via full integration of CO2 production across the wake.

Body-mounted accelerometers provide a new prospect for estimating power use in flying birds, as the signal varies with the two major kinematic determinants of aerodynamic power: wingbeat frequency and amplitude. Yet wingbeat frequency is sometimes used as a proxy for power output in isolation. There is, therefore, a need to understand which kinematic parameter birds vary and whether this is predicted by flight mode (e.g. accelerating, ascending/descending flight), speed or morphology. We investigate this using high-frequency acceleration data from (i) 14 species flying in the wild, (ii) two species flying in controlled conditions in a wind tunnel and (iii) a review of experimental and field studies. While wingbeat frequency and amplitude were positively correlated, R ² values were generally low, supporting the idea that parameters can vary independently. Indeed, birds were more likely to modulate wingbeat amplitude for more energy-demanding flight modes, including climbing and take-off. Nonetheless, the striking variability, even within species and flight types, highlights the complexity of describing the kinematic relationships, which appear sensitive to both the biological and physical context. Notwithstanding this, acceleration metrics that incorporate both kinematic parameters should be more robust proxies for power than wingbeat frequency alone.

Many birds use carotenoids to colour their plumage yellow to red. Because birds cannot synthesise carotenoids, they need to obtain these pigments from food, although some species metabolise dietary carotenoids (which are often yellow) into derived carotenoids (often red). Here we study the occurrence of yellow and red carotenoid‐based plumage colours in the passerines, the largest bird radiation and quantify the effects of potential ecological and life‐history drivers on their evolution. We scored presence/absence of yellow and red carotenoid‐based plumage in nearly 6000 species and use Bayesian phylogenetic mixed models to assess the effects of carotenoid‐availability in diet, primary productivity, body size, habitat and sexual selection. We also test the widespread assumption that red carotenoid‐based colours are more likely to be the result of metabolization. Finally, we analyse the pattern of evolutionary transitions between yellow and red carotenoid‐based plumage colours to determine whether, as predicted, the evolution of yellow carotenoid‐based colours precedes red. We show that, as expected, both colours are more likely to evolve in smaller species and in species with carotenoid‐rich diets. Yellow carotenoid‐based plumage colours, but not red, are more prevalent in species that inhabit environments with higher primary productivity and closed vegetation. In general, females were more likely to have yellow and males more likely to have red carotenoid‐based plumage colours, closely matching the effects of sexual selection. Our analyses also confirm that red carotenoid‐based colours are more likely to be metabolized than yellow carotenoid‐based colours. Evolutionary gains and losses of yellow and red carotenoid‐based plumage colours indicate that red colours evolved more readily in species that already deposited yellow carotenoids, while the reverse was rarely the case. Our study provides evidence for a general, directional evolutionary trend from yellow to red carotenoid‐based colours, which are more likely to be the result of metabolization. This may render them potentially better indicators of quality, and thus favoured by sexual selection.