if get the results from your one-or-the-other query, including annotation values, then you can parse those results and keep only the ones that have both annotation values. some discussion on how to get annotation values from the API here: https://forum.inaturalist.org/t/code-to-extract-annotations-from-exported-json/31950.
a variation of this would be to get the smaller set of records (probably dead birds) and then inspect the annotation values of each of the records in that set, keeping a record if it includes the other annotation value (juvenile) as well.
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other possible methods involve essentially joining the results of two queries. it’s probably easiest to accomplish this using the API, or possibly via CSV exports, rather than going through the regular Explore page.
method 3:
- get list of obs ids for juvenile birds
- get list of obs ids for dead birds
- outside of the system, compare the results of the two lists and get only ids that exist in both lists
method 4:
- get list of obs ids for the smaller set (probably dead birds)
- get list of obs ids for the other set (probably juvenile birds), with an additional
&id=parameter set to the list of observations from the first part.
for an example of how to get a list of observation ids from the API, see https://forum.inaturalist.org/t/search-by-location-accuracy-under-edit-observations-batch-edit/21399/5.