The Limits of eBird Moderation in the Face of Field Reality

Whiskered Tern at New Embankment Wetlands, Danang

By Maurizio Saroli

In the world of birding, few tools have revolutionised citizen science like eBird. It’s a platform that democratises data, connects birders globally and builds a living map of avian movement. But for all its strengths, eBird is not infallible—especially when it comes to the moderation of rarities. The system, reliant on regional reviewers, can sometimes fall into the trap of gatekeeping based on static assumptions rather than dynamic observation. Their work is crucial, yet the process can sometimes default to skepticism when a sighting seems to challenge what is 'normal'. This is understandable—most flagged records do turn out to be misidentifications—but the risk is that valid outliers are filtered out simply because they defy expectations.

Take the case of the Black-naped Tern Sterna sumatrana. A few weeks ago, I submitted a sighting of this coastal species on a river in central Vietnam. The response from the eBird reviewer was swift and dismissive: “Not possible. They would never occur there.” The implication was clear—my observation didn’t fit the expected pattern, so it must be wrong. But birds don’t read field guides. They don’t consult distribution maps before taking flight. And they certainly don’t ask reviewers for permission to explore new habitats.

Three days later, I returned to the same river and photographed the Black-naped Tern in exactly the same location. The image was clear, diagnostic and irrefutable. The bird was there. It had always been there. What changed was not the tern’s behavior—but the human willingness to believe it.

Whiskered Tern, New Embankment Wetlands, Danang.

And this is where the story becomes even more interesting. Seeing a Black-naped Tern on an inland river was not just a 'tick' on a checklist—it was a moment of revelation. For several minutes, I watched it quarter the river like a marsh tern, making repeated plunge-dives for small fish. This was not a lost or confused bird, at least not in the usual sense. It was foraging with skill, seemingly at home in this unexpected setting. That raises fascinating ecological questions: Was this a one-off exploration? Or could inland rivers represent an under-recognised feeding opportunity for this species, at least seasonally?

This isn’t an isolated incident. Across the globe, birders have stories of sightings dismissed because they defy expectations. But expectations are not evidence. They are hypotheses, and hypotheses must yield to data. In this case, the data was a tern, behaving naturally, choosing to fish over a river miles from the coast.

There are plenty of reasons why a bird might appear in an unexpected location:
• Weather systems displace individuals
• Juveniles explore beyond typical ranges
• Habitat degradation forces movement
• Food availability shifts
• Migration routes bend with climate change
• Human infrastructure creates new stopover points
• Birds simply wander

To assume that rarity equals impossibility is to misunderstand the very nature of birds. They are mobile, adaptive and often unpredictable. That’s what makes birding thrilling—and what makes rigid moderation problematic.

It’s important for eBird reviewers to remember that they are supposed to be allies in this process. Their role is not to suppress unusual reports. To keep the database robust and credible they must strike a balance between healthy skepticism and openness to discovery. Ideally, when a sighting challenges norms, it should spark curiosity, questions and collaborative effort.

My personal experience with the local reviewer is a test of patience. The list of sightings I have submitted to eBird which have been removed from public view because the reviewer has no knowledge or experience of those species in the locations where they were observed is growing ever longer. In many instances I was told that my sightings are false only for the same species to be recorded by the same reviewer months, weeks or even days later. Such species include Dusky Thrush Turdus eonomus which I recorded first on 12 October, Eurasian Sparrowhawk Accipiter nisus which I recorded first on 20 January, Grey-headed Fish-Eagle Icthyophaga ichthyaetus which I recorded first on 5 February, and Siberian Stonechat Saxicola maurus which I recorded first on 10 February 2026. In total there are currently 20 sightings that I have submitted for Danang which were removed. Of these, nine are supported by diagnostic photographic evidence and one with a diagnostic audio recording. For stories about some of these species, see Rediscovering Asian Golden Weaver in Central Vietnam, First Record of Purple Sunbird in Central Vietnam and First Record of Red-tailed Laughingthrush in Danang. 

This situation is unfortunate for those birders who live in Danang, but there is an alternative solution. Danang Bird Club is a regional birdwatching society which is home to a growing number of records of bird sightings in Vietnam. All birders are welcome to submit their rare bird sightings to the Danang Bird Club Records Committee. Ordinary bird records are also accepted simply by sharing checklists with the Club eBird account (username: danangbirdclub. The Club also sends out its own Rare Bird Alerts via Facebook and publishes a quarterly Rare Bird Round-up on the DBC News blog. For any birders in the country who are interested in being a part of our community, feel free to get in touch.

Maurizio is the contributing editor of DBC News, part of Danang Bird Club, a non-profit organisation focused on citizen science, education and advocacy for the conservation of Vietnamese avifauna. He is the author of Birdwatching in Central Vietnam; a guide to the region’s rich avian diversity. Originally from London, Maurizio was a member of the British Trust for Ornithology and took part in national bird surveys like the Nest Record Scheme and the Breeding Bird Survey before bringing his passion for ornithology to Vietnam. 

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