None of 28 ozone site switches had complete two-site overlap in matched four-state bird surveys from 2005-2019

We audited changes in the ozone site assigned to repeated bird surveys in California, Oregon, New York, and Pennsylvania in 2005-2019. Only 28 of 1,394 eligible consecutive-year pairs with the same route and observer changed sites. None had at least 24 valid days at both sites in both annual exposure windows. Thus, the planned two-site comparison could not separate annual ozone change from site substitution. An exploratory one-site comparison was possible for 23 pairs. Site substitution contributed at least 2 ppb to 11 differences, and five differences reversed sign with a fixed site. A common-relative-day check reduced sign reversals to three of 22 pairs. Same-site matching removed few pairs in this selected panel, but this does not bound ecological model bias. Missing overlap, sparse switches, exposure error, and selection limit inference. We do not estimate an ozone or climate effect on birds. The package includes source hashes, daily evidence, pair records, code, figures, and offline checks.

ozone · birds · exposure error · observation bias · monitor selection · Breeding Bird Survey · data overlap