Climate, habitat, and socioeconomic gradients shape divergent occupancy and co-occurence patterns between two hummingbirds in western North America.

Climate and land-use change are reshaping species distributions and biotic interactions, yet assessments of these processes across broad spatial extents remain limited. Using 2023 eBird records from spring and early summer on the breeding grounds, combined with high-resolution environmental predictors, we modelled occupancy of Anna's hummingbird (Calypte anna), an increasing and range-expanding species, and rufous hummingbird (Selasphorus rufus), a declining species, across 1.1 million km2 of western North America. Single-species occupancy models revealed similar detectability patterns and affinities for coniferous and shrub habitats with low canopies (≤ 15 m), but marked divergence in climatic preferences and responses to human-modified landscapes. Rufous hummingbird was associated with colder climates, low urban cover (< 25%), and low-to-moderate cropland, whereas Anna's was associated with warmer conditions and showed greater affinity for urban environments. Multispecies occupancy models showed that co-occurrence was highest in areas with low-to-moderate urbanisation and high Gross Domestic Product (GDP), consistent with the 'Luxury Effect' hypothesis. However, co-occurrence declined sharply in highly urbanised, high-GDP areas. Anna's occupancy increased steadily with GDP across the urban-rural gradient, whereas rufous responded positively to GDP only where urbanisation was low. We hypothesize that this divergence could reflect differential environmental filtering rather than direct competition: the resident Anna's hummingbird may be better able to exploit year-round anthropogenic resources, use simplified urban vegetation, and establish breeding territories earlier, whereas the migratory rufous hummingbird may remain more dependent on structurally complex semi-natural habitats and on the seasonal availability of suitable resources along its migration route and within its breeding range. Overall, climate, habitat, and socioeconomic gradients jointly shaped occupancy and co-occurrence patterns in these contrasting species.