The research team, led by Silvia Bainy Gastal of the Federal University of Rio Grande (FURG), together with Carolina Silveira Mascarenhas and Leandro Bugoni, examined the nasal cavities of 171 Kelp Gulls collected between 2015 and 2022 in the Brazilian states of Rio Grande do Sul, Santa Catarina, São Paulo and Rio de Janeiro. Most of the birds (146 individuals) had died under care at marine animal rehabilitation centers, while 25 were recovered during routine beach surveys. All carcasses were collected within 24 hours of the animal’s death, and none of the examined birds had received any antiparasitic treatment, ensuring that the mite counts reflected natural infection levels rather than the effects of medication.

Of the 171 gulls dissected, 56 — or 32.7 percent — were parasitized by rhinonyssid mites, and every specimen identified in the analyzed subsample proved to be Larinyssus orbicularis, a species first described in 1948 and known to specialize on gulls and terns. In total, the researchers recovered 2,224 mites, with a mean abundance of 13.0 mites per host across the whole sample and a mean intensity of 39.7 mites per parasitized bird. The species was confirmed using both light microscopy and scanning electron microscopy, the latter proving essential because the dorsal plates that serve as the mite’s diagnostic features were difficult to resolve with conventional optical equipment. Supplementary characters, including the shape and dimensions of the idiosoma, leg length, and the chaetotaxy of the dorsum, venter and gnathosoma, all matched the original description of L. orbicularis.

One of the study’s most striking results concerns infection intensity. Individual burdens ranged from a single mite to the record-setting 197, and because no standardized classification of Larinyssus infections in gulls existed before, the team proposed a semi-quantitative scheme based on the distribution of counts they observed: low infections of 1 to 20 mites, moderate infections of 21 to 50, and heavy infections exceeding 50 mites. Under this framework, 48.2 percent of parasitized gulls fell into the low category, 30.3 percent into the moderate category, and 21.5 percent carried heavy infections — meaning that roughly one in five infected birds hosted a substantial parasite load capable of occupying much of the nasal cavity.

Anatomically, the mites occupied the full length of the upper respiratory tract, from the rostral nasal conchae through the middle and caudal conchae. In heavily parasitized birds, the parasites were also found around the choana — the nasal opening of the palate — and very close to the nostrils, in some cases visible externally through the nares. Gross pathological examination revealed that most mites adhered to host tissue with only limited mucus, but in some individuals the researchers observed accumulated mucoid material, including tenacious mucus and bloody tenacious mucus surrounding the parasites. These observations echo earlier findings in Gouldian Finches infected with the related mite Sternostoma tracheacolum, suggesting that respiratory mite infections may produce similar mucosal changes across widely divergent bird groups.

Statistical analysis of the parasitological indices revealed a clear age-related pattern. Prevalence did not differ between male and female gulls, a result consistent with studies of Rhinonyssidae in other hosts such as the Rosy-billed Pochard and the Magellanic Penguin, and one that the authors interpret as evidence that transmission — whether during parental care or after fledging — is carried out equally by both sexes in these monogamous birds. Age, however, mattered significantly: only 11.8 percent of juveniles were infected, compared with 43.3 percent of immatures and 36.4 percent of adults. This mirrors the classic pattern reported by TerBush in 1963 for Herring Gulls in the United States, where juveniles showed similarly low infection rates, and supports the hypothesis that mite transmission to young gulls occurs predominantly after chicks have left the nest rather than inside the colony.

Geographically, the picture was equally telling. Of the 56 parasitized hosts, 55 were collected in Santa Catarina and just one in Rio Grande do Sul, while no mites were found in any of the gulls from São Paulo or Rio de Janeiro, despite those states contributing a smaller but meaningful number of carcasses. The authors caution that limited sampling in the northern states may partly explain the absence of positive records there, but they also point to host ecology as a plausible driver. In Brazil, Kelp Gulls breed on coastal islands along roughly 850 kilometers of shoreline, from Laguna in Santa Catarina northward to Rio de Janeiro, and the species relies on the coastal zone for foraging and resting. Because gulls gather in groups — including mixed flocks with tern species known to carry the same mite species — areas of high host density and overlapping species distributions may foster both intra- and interspecific mite transmission, shaping the observed latitudinal gradient in prevalence.

The transmission biology of rhinonyssid mites adds further ecological context. These obligate, blood-feeding endoparasites typically disperse through direct contact, moving between hosts when infected adults regurgitate food to nestlings or during courtship, although indirect transmission across water, perches and contaminated surfaces has also been documented. The researchers suggest that L. orbicularis, naturally associated with Kelp Gulls, may occasionally spill over into terns that share the same coastal environments, much as captive canaries have become secondarily infected with other rhinonyssids in regions where they were introduced. Such dynamics could help explain why the same mite species shows markedly different prevalence in different hosts — 9.1 percent in South American Terns and 50 percent in Cabot’s Terns in an earlier Brazilian study, versus 32.7 percent in Kelp Gulls here, and 24.8 percent and 4.5 percent in Herring Gulls previously examined in the United States and Russia respectively.

While rhinonyssids are generally considered to cause limited harm, the literature documents a range of potential pathologies: injury to the nasal epithelium and blood vessels, pulmonary congestion, rhinitis and sinusitis, and in captive birds even anorexia, aphonia, cachexia, air-sac inflammation, tracheitis and pneumonia that can prove fatal. The authors emphasize that future work should incorporate histopathological analysis of nasal tissues in parasitized gulls to determine whether L. orbicularis infections are associated with tissue lesions or respiratory disease, and they advocate for observations of clinical signs during rehabilitation combined with postmortem examinations as a practical pathway for studying live-host interactions. Because nasal mite infections cannot yet be readily diagnosed in living birds, carcasses from rehabilitation centers represent an invaluable but underused window into this hidden facet of avian health.

Ultimately, the study expands the known geographic distribution of L. orbicularis in Brazil, delivers the largest parasitological dataset ever compiled for nasal mites in gulls, and sets a methodological benchmark by demonstrating the value of scanning electron microscopy for species-level identification. The record intensity of 197 mites in a single bird, and the substantial proportion of heavily infected hosts, together make a compelling case that these minute inhabitants of the nasal cavity deserve far greater attention from ornithologists, parasitologists and wildlife rehabilitators alike. Whether Kelp Gulls have simply learned to tolerate their tenacious tenants, or whether the heaviest burdens carry hidden costs to survival and reproduction, remains an open question — but one that this new baseline now makes possible to answer.

Subject of Research: Prevalence, geographic distribution and parasitological indices of the nasal mite Larinyssus orbicularis in Kelp Gulls (Larus dominicanus) in Brazil

Article Title: Nasal Mites of Kelp Gulls (Larus dominicanus) in Brazil: Geographic Distribution and Parasitological Indices

Article References: Nasal Mites of Kelp Gulls (Larus dominicanus) in Brazil: Geographic Distribution and Parasitological Indices. (n.d.). https://doi.org/10.1007/s11686-026-01396-w

Image Credits: AI Generated

DOI: 10.1007/s11686-026-01396-w

Keywords: Kelp Gull, Larus dominicanus, nasal mites, Larinyssus orbicularis, Rhinonyssidae, parasitology, seabirds, Brazil, infection intensity, prevalence, scanning electron microscopy, host-parasite interaction

The research, conducted by M. Candelaria Biagiotti Barchiesi, Germán O. García, Melina V. Castano, and Laura M. Biondi of the Instituto de Investigaciones Marinas y Costeras at the Universidad Nacional de Mar del Plata and CONICET, focused on a species that has become a textbook example of ecological flexibility. Kelp Gulls are generalist foragers with a remarkably diverse repertoire of feeding tactics, from probing intertidal mudflats to scavenging at waste facilities and even preying on other seabirds. Because these birds frequently feed on anthropogenic food resources, the team hypothesized that social learning might play a central role in how individuals discover and master new ways of exploiting them. To test this idea rigorously, they designed a controlled experiment in which naïve gulls, birds with no prior experience of the task, were given the opportunity to watch a demonstrator solve a problem before attempting it themselves.

The experimental apparatus was an opaque box containing food, a classic extractive foraging task that requires the animal to discover that a specific action, in this case manipulating the lid, releases the reward. Because the box was opaque, success could not be achieved by simply seeing the food; the birds had to learn the technique itself. The study involved twenty-five naïve observer gulls, thirteen adults and twelve immatures, along with six control individuals that received no demonstration. In a baseline phase conducted before any demonstration took place, only twenty-eight percent of the future observers and thirty-three percent of the controls managed to solve the box on their own, confirming that the task was genuinely difficult for an uninstructed gull. This low baseline success rate set the stage for a clean test of whether social information could change the odds.

The results were striking. During the test phase, after observers had watched a demonstrator open the box, not a single control bird solved the task, while fifty-two percent of the observers succeeded. In other words, watching a companion roughly doubled the probability of success compared with the observers’ own baseline performance, and it made the difference between total failure and moderate success relative to uninformed birds. The effect, however, was not uniform across all ages. Only adult observers were significantly more successful and significantly faster at both contacting the box and solving it, both compared with the control group and compared with their own pre-demonstration attempts. This age-specific pattern suggests that adult gulls may be better positioned to translate observed information into effective action, perhaps because of greater motor competence, stronger motivation, or more refined attention to the demonstrator’s behavior.

Intriguingly, the study found no differences in overall performance between age classes either before or after the demonstration, indicating that immatures were not inherently worse at the task once they had the same social information. Nor did the age of the demonstrator matter: observers learned equally well whether they watched an adult or an immature bird performing the technique. The demonstrator’s own neophobic response, its hesitancy or boldness around the novel box, also failed to predict whether observers succeeded. These null results are informative in themselves. They suggest that the critical ingredient in social transmission here was the demonstrator’s technique rather than its social status or emotional demeanor, and that gulls of any age can serve as effective sources of social information within a flock.

One of the most technically interesting aspects of the study was its use of a two-action design, in which different demonstrators could be shown using different lid-opening techniques. This allowed the researchers to ask not merely whether observers learned, but what they learned. The answer was clear: observers predominantly adopted the specific technique used by their demonstrator, and immatures showed greater consistency than adults in copying the exact lid type they had seen opened. This fidelity to the demonstrated method is a hallmark of true social learning rather than mere local enhancement, the simpler process in which an animal is merely attracted to a location or object by another’s presence. By matching the demonstrator’s action, the gulls demonstrated that they had extracted procedural information from observation, effectively copying a foraging behavior they had never performed themselves.

The implications of these findings extend well beyond the aviary. Landfills and other urban food subsidies bring large numbers of gulls into close and repeated contact, creating ideal conditions for social transmission of novel foraging innovations. If one inventive individual discovers a new way to access food, whether opening a container, exploiting a new waste stream, or targeting a novel prey, social learning provides a fast track for that innovation to spread through the population. This dynamic helps explain how generalist species like the Kelp Gull can rapidly adjust their behavior to changing environmental conditions, a capacity that is increasingly valuable as urbanization transforms coastal ecosystems across the Southern Hemisphere and beyond. It also raises practical considerations for wildlife management, since behaviors learned socially can be difficult to reverse once established in a local population.

The study also contributes to a broader scientific conversation about cognition in seabirds, a group historically understudied relative to primates, corvids, and parrots. Gulls belong to the charadriiform birds, and accumulating evidence now points to sophisticated cognitive abilities within this lineage, including problem-solving, behavioral flexibility, and social responsiveness. The present experiment adds a controlled, quantitative demonstration that Kelp Gulls possess the capacity for observational learning of an extractive foraging task, placing them firmly within the growing roster of species whose ecological success is underpinned by social cognition. The combination of diverse foraging tactics, cognitive ability, and social transmission appears to be a potent recipe for thriving in human-dominated landscapes.

Methodologically, the work reflects careful attention to animal welfare and experimental design. The gulls were captured with adherence to Argentine legal requirements and guidelines for the use of animals in research, with the experimental protocol approved by the National University of Mar del Plata Animal Ethics Committee. All birds were housed with veterinary assistance during their stay in the aviary and were released at their original habitats once testing was complete. The research was funded by Argentina’s Agencia Nacional de Promoción de la Investigación, el Desarrollo Tecnológico y la Innovación, and the authors acknowledge the cooperation of workers at the Mar del Plata Landfill, whose daily reality alongside these birds provided the inspiration for the study.

As cities continue to expand and wildlife increasingly shares space with people, understanding the mechanisms of behavioral adaptation becomes ever more urgent. This study of urban Kelp Gulls offers a vivid reminder that the animals flourishing around us are not merely lucky scavengers but capable learners, watching one another, copying successful techniques, and building shared behavioral traditions that ripple through their flocks. In the gull rifling through a landfill, scientists are glimpsing the cognitive machinery that allows some species to turn humanity’s footprint into opportunity, one observed behavior at a time.

Subject of Research: Social learning of a novel foraging task in immature and adult urban Kelp Gulls

Article Title: Social learning of a foraging task in immature and adult urban Kelp Gulls (Larus dominicanus)

Article References: Biagiotti Barchiesi, M. C., García, G. O., Castano, M. V., & Biondi, L. M. (2026). Social learning of a foraging task in immature and adult urban Kelp Gulls (Larus dominicanus). Animal Cognition. https://doi.org/10.1007/s10071-026-02102-z

Image Credits: AI Generated

DOI: 10.1007/s10071-026-02102-z

Keywords: Kelp Gull, social learning, animal cognition, urban wildlife, foraging behavior, seabirds, behavioral flexibility, urbanization, two-action task, social information, extractive foraging, Larus dominicanus