Date: 3/25/26 3:17 pm From: Kevin Schwartz via groups.io <kdschwartz...> Subject: Re: [EBB-Sightings] eBird filters, and what to do when something is "rare"
Thank you, Ethan for all you do for eBird! We appreciate you and this was a
great write up about why things are getting flagged.
Kevin
*Kevin Schwartz, PhD*
*Principal Biologist/Wetland and Ecological Restoration Manager*
ISA Certified Arborist (#WE-9541A)
ISA Qualified Tree Risk Assessor
CRAM Wetlands Official Practitioner
Olberding Environmental, Inc.
https://olberdingenvironmental.com/
On Wed, Mar 25, 2026, 11:22 AM Ethan Monk via groups.io <z.querula=
<gmail.com...> wrote:
> And for those of you asking "WHY" – why do I have to include a
> description? We know the spring is early, why can’t you just accept it?
>
> There are, I think, two good answers.
>
> First, the philosophical/doctrinal one. If Species X arrives on the
> average date of March 15th, and this year the first arrivals are March 7th,
> even though by March 11th the species may seem “ho-hum” and clearly, they
> are here, historically the date is still quite significant, even though it
> may not be significant in the context of this specific season.
>
> If that is not convincing, reason two is that data is always subject to
> revision. At any time now or in the future, an eBird reviewer can go into
> the database and update decisions that they think were wrong. We try not to
> do this frequently, because it is probably a good idea to trust the
> contemporaneous eBird reviewer, but that does not always happen for a
> number of reasons. The classic example are Golden-Plovers. In the early
> days of California birding, most birders thought (what is today known as)
> American Golden-Plovers were the common species in California, and Pacific
> Golden-Plovers were the rarest species. It was eventually realized that the
> exact opposite is the case, Pacifics are the commonest of the two species
> in California, and American the rarest, and a bunch of old records were
> revised to account for that mistaken understanding. If you were going back
> and reevaluating old records of American Golden-Plovers, would you be more
> likely to throw out records with or without field notes? I know my answer.
> That is not to say that in the future we will realize the early Western
> Flycatchers may be another species of Empidonax, for example, but rather a
> more stringent reviewer may decide to “clean-up” the data, or similar. And
> the records with no supporting field notes are more likely to be discarded,
> even if accurate, because… there is nothing there to support them.
>
> Thanks.
>
> Ethan M
>
> On Wed, Mar 25, 2026 at 11:06 AM Ethan Monk <z.querula...> wrote:
>
>> Hi all,
>>
>> Happy spring. If you use eBird, and would not mind reading for a second,
>> that would be greatly appreciated.
>>
>> As many people have noticed, it is an early spring, with many birds like
>> Wilson's Warblers and Cassin's Vireos arriving well before they normally
>> do. In Contra Costa County (and in many other counties, it is similar) the
>> eBird filters are set to mark many species "rare" until several days after
>> the all-time, record early spring arrival date. For example, the earliest
>> historical arrivals for Cassin's Vireo in Contra Costa County history are
>> right around March 21st-24th, so they are flagged as rare until March 27th.
>> Early reports are more significant, and so are more deserving of scrutiny,
>> and perhaps are more likely to be wrong (this is especially true in the age
>> of Merlin, which uses some form of probability model when suggesting
>> species identifications). This means that in early springs, like this one,
>> active birders might be flagging the filter a lot, as large waves of spring
>> migrants arriving earlier than typical will often flag as "rare."
>>
>> So-- I am out eBirding, and I have found a species that flags as
>> rare--what do I do? The "rare" designation is the system's way of telling
>> you that it wants information to substantiate the sighting. How much
>> information is needed is going to depend on the context, for example an
>> aseasonal Western Tanager and a Spotted Redshank will produce the same
>> response from the system ("rare"), but clearly require different levels of
>> documentation. But, if something flags as rare, always always always some
>> helpful information is needed. Writing something like "in pine tree" is
>> only valuable in confirming that it was not a "pocket-click," and thus is
>> not helpful really at all. In springs like this one, when many things are
>> early, the early context can be taken into account, so not much information
>> is needed at all, but again something is needed.
>>
>> For many spring early arrivals, consider writing ~one sentence describing
>> field marks you observed that led you to the ID. Otherwise, I will send you
>> an email asking for more documentation, and that just creates more work for
>> you and for me :) Even better if you can include something that indicates
>> you understand why a species is rare, but this is not necessary. Going back
>> to the Western Tanager example, say you see an early adult male Western
>> Tanager tomorrow... what would be an ideal description? Well, it is a week
>> or so early, about in line with many other early arriving species this
>> spring. Something like "Early-- red head, bright yellow body, black wings"
>> would probably get the job done. Even better, although absolutely not
>> necessary, if you could write something like "this is an early spring...
>> red head, bright..." That way people looking back on the eBird checklist in
>> future years will have some additional context.
>>
>> Thank you for considering.
>>
>> Ethan Monk
>> (a Contra Costa County eBird Reviewer)
>>
>
>
>
>
