10 February 2025
When you count birds next weekend for the Great Backyard Bird Count eBird has a lot of advice on how to do it. There are pages and pages on how to be accurate but for me the easiest counting error to fix is this: Don’t forget to count non-native species.
At the end of every eBird checklist the app asks, “Are you submitting a complete checklist of the birds you were able to identify?”
- “YES” means “I wrote down every species.”
- It also means that during data analysis researchers can infer that “No other species were present.”
If you don’t include pigeons, house sparrows or starlings but you answer YES you have biased your results.
Observer selection bias occurs when the evidence presented has been pre-filtered by observers. … The data collected is not only filtered by the design of experiment, but also by the necessary precondition that there must be someone doing a study.
— WIkipedia: Selection Bias
Some observer bias is hard to eradicate but this one is easy. YES there are pigeons on this light pole. Tell eBird how many.
Don’t worry that they are non-native. eBird colors the map orange outside their native range. Your checklists update the rock pigeon (Columba livia) map worldwide.
So remember to count all the birds you see and hear during the Great Backyard Bird Count.
Every pigeon counts!