Migration Pattern Calculator

The calculator's baseline peak dates are pinned to 40°N, and every degree of latitude away from that reference shifts the spring peak by 2.5 days — later as you move north, earlier as you move south — since birds reach higher latitudes later in spring as conditions thaw progressively northward. The fall peak gets a similar but smaller adjustment (80% of the spring shift, in the opposite direction) because southbound birds pass higher latitudes earlier in the fall. A flyway-specific offset is then layered on top of the latitude adjustment.

Shorebirds are modeled as moving through in a tighter pulse than waterfowl, songbirds, raptors, or seabirds, so their window (input speciesGroup value 2) is set to 21 days centered on the peak while the other four groups all share a 35-day window. This is a fixed assumption per species group rather than something calculated from your other inputs, and it's the window used to classify whether your entered day-of-year falls in spring migration, fall migration, breeding season, or wintering.

The calculator adds 70% of your entered wind speed directly onto the species group's baseline cruising speed — so a 20 km/h tailwind adds 14 km/h to the baseline, not the full 20. That adjusted speed can never drop below 30% of the baseline even if you enter 0 wind, since the model doesn't represent headwinds as a negative adjustment. The adjusted speed then divides into the latitude-derived migration distance to get flying days, which combine with stopover time for the total migration duration.

Energy cost uses a simplified version of the Pennycuick flight-power model: cost per kilometer scales with body mass raised to the 0.75 power, then that per-km figure is multiplied by the estimated total migration distance (which itself is derived purely from latitude, at 110 km per degree above 20°N). It's meant as a relative indicator of how metabolically expensive the migration is for a given body size and distance, not an exact physiological measurement.