Assistant status gave no clear temperature-slope difference in Canada and US bird surveys in 1985-2024

We tested whether the start-temperature slope of recorded bird taxa differed when an assistant recorded the observations. We used 59,238 consecutive-year pairs with the same route and observer in Canada and the US, in 1985-2004 and 2005-2024. Assistant minus no-assistant slopes were -0.347, -0.069, +0.007 and +0.035 taxa per 5 C. All four intervals adjusted for multiple tests included zero. US intervals were within -0.25 to +0.25 taxa per 5 C under the model. Canada intervals were wider. Checks with unchanged assistant status, close survey dates and observer clusters gave no clear difference. This result does not show that assistants remove weather bias. An assistant records data and is not a second independent bird observer. Selected surveys, missing assistant reports, detection, unmeasured change and few year clusters limit inference. The package includes data, code, source hashes, model inputs and checks.

biodiversity · observation bias · temperature · Breeding Bird Survey · assistant · effect modification · null result