Table 1 Migratory traits and how the data was collated

Migration type

Is the species a partial or complete migrant? (Yes/No)

[15]

Migration distance

Great circle distance (km) between the breeding range centroid and non-breeding centroid

Derived from [73] and [14]

Cohort timing

Do juveniles migrate before, concurrently, or after adults?

[25] (see SM2), [15]

Flocking

Does the species flock on migration? (Yes/no)

[8, 9, 15]

Flocking behaviour

Species flocking behaviour (mixed-age flocks, age-separated flocks, or solo)

Combination of cohort timing and flocking variables

Absolute population trend

Survey-wide loglinear population trend based upon Breeding Bird Survey data (%/yr 1966–2019 for the Core Survey Area). Absolute value taken

[67]

Generation length

Modelled generation length based upon age of first reproduction, maximum longevity, and annual adult survival

[13]

Migratory timing

At what time does the specie primarily migrate? (day or night)

[8, 9, 15]

Habitat specialism score

How specialised is the species to a certain habitat (0–100)

Derived from Wilman et al. [86] as maximum score across habitat classes

Diet specialism score

How specialised is the species to a dietary niche (0–100)

Derived from Wilman et al. [86] as maximum score across diet classes

Total breeding range size

Total size of the breeding range (km²) restricted to the Americas

Derived from [73] and [14]

Sampled breeding range size

Size of the breeding range (km²) covered by the analysis strata (Figure SM2)

Derived from [73] and [14]

Total non-breeding range size

Total size of the non-breeding range (km²) restricted to the Americas

Derived from [73] and [14]

Sampled non-breeding range size

Size of the non-breeding range (km²) covered by the analysis strata (Figure SM2)

Derived from [73] and [14]