Wingbeats

Wingbeats analyzes eBird checklist data for Knox County, TN to estimate typical migration timing for each species. The analysis covers the 10 most recent complete calendar years (2016–2025), drawn from 85,135 checklists.

For each species, a weekly detection frequency is calculated — the proportion of checklists that recorded the species in a given week. This is then smoothed with a circular 3-week moving average that wraps around the calendar year, so winter visitors whose presence spans December–January are handled correctly.

Migration status is determined by analyzing the smoothed frequency curve for a sustained absence. The algorithm searches for the longest consecutive run of weeks where activity drops below a threshold (10% of peak frequency or 0.5%, whichever is greater). If this gap spans at least 6 weeks, the species is a candidate for migratory classification. To guard against seasonal detection bias — some resident species simply become harder to detect at certain times of year — a gap depth verification step requires that the gap be truly empty: either the mean frequency during the gap is < 3% of peak, or the gap is 20+ weeks long and at least 30% of those weeks have near-zero raw detections (< 0.1%). This second condition prevents species with year-round detectability but low seasonal observations from being misclassified as migrants. Species that pass all checks are classified as migratory.

All migration classifications reflect detection patterns within Knox County, TN only and should not be interpreted as representing a species' behavior across its full range. Many species have both migratory and year-round resident populations depending on geography — a species classified here as migratory may be sedentary in other parts of its range, and vice versa. Additionally, species with sparse local records may occasionally be classified as migratory due to factors other than true seasonal movement, such as juvenile dispersal, rather than a consistent annual migration pattern.

Arrival and departure weeks are set to the boundaries immediately surrounding the absence gap — arrival is the first week after the gap ends, and departure is the last week before it begins. Peak migration is the week with the highest smoothed detection frequency.

Confidence is scored on a 0–99% scale combining year coverage (60% weight) and checklist volume (40% weight, log-scaled). Species observed in fewer than 4 of the 10 years or with confidence below 65% are flagged as Rare. These very rarely reported species are excluded from migration alerts and the main timeline despite being almost exclusively migratory — with so few records, their apparent migration windows are unreliable.

Citation: eBird Basic Dataset. Version: EBD_relJan-2026. Cornell Lab of Ornithology, Ithaca, New York. Jan 2026. Data provided by eBird. Taxonomy from the eBird/Clements Checklist.