If a pelican walks toward you on the beach, something is wrong with that bird. Don’t touch it. Sick, disoriented and dead pelicans have been turning up along Costa Rica’s Pacific coast since late June. Two months on, nobody has worked out what is killing them. Start with the question most people actually want answered.
It is not bird flu — at least not in anything tested so far. SENASA has processed 121 samples from 59 wild birds through August 10, covering pelicans, boobies, blue-footed boobies, hawks, owls and parakeets, and everyone came back negative for avian influenza. Tests for Newcastle disease came back negative as well, and the agency says nothing so far links the deaths to either virus. Negative results are not an answer, though.
They only rule things out. Randall Arguedas, who heads epidemiology at SENASA, points out that wild bird die-offs can come from a long list of causes — other infectious agents, poisoning, environmental conditions, nutritional problems — and that sorting between them takes more than viral screening.
The investigation has widened accordingly, into clinical assessments, tissue studies and necropsy findings, with SENASA, SINAC, the Health Ministry, Universidad Nacional and wildlife rescue centres all working the same problem.Arguedas is blunt that no single cause can be pinned down yet, and that whatever conclusion comes will have to rest on lab work rather than guesswork.
The pelicans are the bulk of what’s been examined. Nineteen of them account for 39 of the samples, alongside five blue-footed boobies and seven other boobies. There is one confirmed bird flu case in the country, and it is worth understanding because it is why this got attention in the first place.
In June a blue-footed booby found at Manuel Antonio tested positive for highly pathogenic avian influenza, type A, subtype H5 — Costa Rica’s first case since 2023. Sick pelicans started appearing shortly afterwards, and the timing alone was enough to make people assume the two were connected. So far the lab work says they aren’t.
What you would actually notice, if you came across one, is the behavior. Biologist Rodolfo Vargas, who founded Refugio Animal Costa Rica, has flagged pelicans approaching swimmers as abnormal for the species here, and counted 13 birds in that condition around Guanacaste over a matter of weeks. Reports have clustered in Guanacaste and around Jacó, with affected birds appearing weak, disoriented, or struggling to fly.
A healthy pelican wants nothing to do with you. One that lets you walk up to it is telling you it’s ill. So, leave it where it is and don’t handle sick or dead birds, and report what you’ve found so the people with protective equipment and a diagnostic protocol can deal with it. The nearest SINAC or SENASA office is the right call, and reporting promptly matters more than anything you could do yourself.
Resist the urge to move the bird somewhere shadier or carry it to a vet. You risk exposing yourself to something nobody has identified yet, and you remove the animal from the location where investigators need to find it. Keep your dog well away, and wash your hands if you’ve touched anything nearby.
None of this is a reason to change your beach plans. A handful of sick birds across a coastline this long is not an outbreak affecting people, and no health authority has restricted access to any beach. It is a reason to look, not touch, and to make one phone call if you see something wrong.
Two months of negative tests means the answer, when it arrives, is likely to be something less obvious than a virus.
Facts Only
* 121 samples were processed from 59 wild birds through August 10.
* Tests for avian influenza returned negative across all tested species (pelicans, boobies, hawks, owls, parakeets).
* Tests for Newcastle disease also returned negative.
* The investigation includes clinical assessments, tissue studies, and necropsy findings.
* Nineteen pelican samples accounted for 39 of the total samples examined.
* A confirmed avian influenza case was reported in a blue-footed booby in June.
* Biologists have flagged abnormal behavior in some pelicans approaching swimmers near Guanacaste.
* Authorities advise reporting sightings to SINAC or SENASA.
Executive Summary
Sick, disoriented, and dead pelicans have been observed along Costa Rica’s Pacific coast since late June, though the cause of death remains undetermined. Health authorities have tested 121 samples from 59 wild birds, including pelicans, boobies, hawks, owls, and parakeets, for avian influenza and Newcastle disease, with all tests coming back negative. Epidemiologists suggest that bird die-offs can stem from various causes beyond viral infection, such as other infectious agents, poisoning, environmental conditions, or nutritional problems, requiring clinical assessments and tissue studies to determine the cause.
The investigation focuses on pelicans, which account for the majority of samples examined. An initial confirmed case of highly pathogenic avian influenza was noted in a blue-footed booby in June, which preceded the appearance of sick pelicans, though laboratory results have not established a direct link between the two events. Biologists have noted abnormal behavior in some pelicans, such as approaching swimmers, suggesting illness or disorientation. Authorities advise that people should not touch sick or dead birds and to report findings to SINAC or SENASA for proper investigation, rather than attempting self-intervention.
Full Take
The narrative of an undetermined cause, where negative testing stalls the inquiry, establishes a pattern of institutional hesitation when faced with complex ecological events. The focus shifts from immediate threat management (handling the birds) to systemic investigation (identifying the unknown etiology), which mirrors the scientific reality that causality often resides in multifactorial environmental or toxicological contexts rather than single pathogens. The emphasis on the behavior of the animals—the visual cue that signals distress—juxtaposed against the negative laboratory results creates a tension between observable symptomology and quantifiable data. This dynamic can be read as an implicit challenge to the authority's ability to define reality through standardized testing alone. The reluctance to assign blame or conclusion suggests a systemic pattern where complexity is managed by avoidance, potentially obscuring underlying environmental correlations that are often the true drivers of ecological distress. What is not directly tested—the environmental and nutritional factors mentioned—represents the vast, unquantified space that dominates the final outcome.
Bridge Questions: If negative testing across multiple known viral agents persists, what specific non-viral or environmental indicators should be prioritized in future investigations? How can public pressure effectively bridge the gap between observational symptoms and delayed scientific conclusions when immediate action is advised? What ethical framework governs the withholding of potential causes when mass animal mortality occurs without a singular diagnostic marker?
Sentinel — Human
The text reads like an investigation synthesizing official health data with field observations and expert commentary, exhibiting the characteristic flow of human-driven reporting on complex, unresolved issues.