CHANGES IN SPRING ARRIVAL DATES OF RUFOUS HUMMINGBIRDS (SELASPHORUS RUFUS) IN WESTERN NORTH AMERICA IN THE PAST CENTURY

摘要

Warming temperatures have been linked to advancing spring migration dates of birds, although most studies have been conducted at individual sites. Problems may arise ecologically if birds arrive or depart before or after associated food resources such as plants or insects reach critical lifecycle stages. Here, I compare mean first arrival dates of the Rufous Hummingbird (Selasphorus rufus), a prolific pollinator and long-distance migrant with the northernmost breeding range of any North American hummingbird, between 1895-1969 and 2006-2015 at eight observation locations in Oregon, Washington, and British Columbia. Historical arrivals were reported through the North American Bird Phenology Program, and recent arrivals were estimated from temporal occupancy patterns using eBird checklists. Results indicated that hummingbirds arrived 8 and 11 days later in the recent time period in two coastal cities in Oregon and 7-17 days earlier in northern, more inland cities in Washington and British Columbia. Fewer days were noted between arrivals in more northerly areas in the recent time period suggesting that birds may now be migrating faster than in the previous time period. Spring temperatures have increased in the past century in much of this region, and birds arrived earlier in years with warmer spring temperatures to suggest that migratory advances are climate-related. Later mean first arrivals reported in coastal regions of Oregon in the recent time period may suggest that Rufous Hummingbirds are bypassing coastal areas to take advantage of more predictable conditions along inland migratory routes or are shifting their breeding ranges northward, notions both supported by declining population trends observed in Breeding Bird Survey data. My results demonstrate a climate-related advancement of Rufous Hummingbirds in western North America and provide justification for the investigation of the ecological impacts of climate change on birds in coastal vs. inland environments. In addition, I provide a framework for comparing information from two extensive and emerging datasets to better understand the impacts of climate change on birds at broad spatial and temporal scales.