Geographic and Temporal Variation in Annual Survival of a Declining Neotropical Migrant Hummingbird (Selasphorus rufus) Under Varying Fire, Snowpack, and Climatic Conditions

Alison J. Moran,Anna Drake,Christine A. Bishop,Scott Wilson

doi:10.3389/fevo.2022.825026

Abstract

Rufous hummingbirds (Selasphorus rufus) have shown consistent declines in abundance since 1970, with an acceleration in this trend starting in the mid-2000s. Demographic data is needed to isolate possible drivers. We employ mark-recapture data to calculate sex-specific adult apparent annual survival, accounting for residency probability, within the coastal and interior regions of British Columbia, Canada between 1998 and 2017. For the coastal region, we also examine associations between apparent survival and a suite of migratory factors: the amount of recently and historically burned flyway habitat, fall moisture availability in the alpine (snowpack), and a broad-scale climate index (SOI), under the assumption that these factors are associated with food availability during a critical period of the annual cycle. We find no trend in adult apparent survival over the 20-year period, implicating changes in recruitment rather than adult survival as driving the declining trend in abundance. Interior birds of both sexes showed lower residency probability than coastal individuals suggesting interior sites captured more late northbound individuals or more early southbound individuals within the breeding period. Adult apparent annual survival was not correlated with any of the migratory variables we examined. Our findings suggest a need to focus on juvenile recruitment as a possible driver of the long-term declines in Rufous Hummingbirds. Future studies should consider both potential threats to productivity on the breeding grounds and to juvenile survival on the non-breeding grounds.

Highlights

The broad-scale annual movements of migratory bird species make them both vulnerable and more difficult to conserve than residents (Lin et al, 2020)
Rufous hummingbirds occupy diverse habitats over their annual cycle and threats to this species could originate over a broad geographical area: their nonbreeding range encompasses the Mexican plateau, Sierra Madre, and western regions of Mexico as well as the southeastern United States, while their breeding range extends across much of western North America, as far north as coastal southeastern Alaska (Healy and Calder, 2006; Moran et al, 2013; Fink et al, 2020)
Our models provide the first measures of adult apparent annual survival for Rufous hummingbirds and only the third estimate for migratory hummingbird species as a group

Summary

Introduction

The broad-scale annual movements of migratory bird species make them both vulnerable and more difficult to conserve than residents (Lin et al, 2020). As the smallest Nearctic-Neotropical migrants, the thirteen hummingbird species that breed within temperate North America represent a difficult group to study (Partners in Flight, 2021). Rufous hummingbirds (Selasphorus rufus) are designated as near-threatened by the IUCN (BirdLife International, 2021) and are considered a priority species for conservation and/or stewardship in two Bird Conservation Regions (ECCC, 2019). Their abundance has declined by 65% since 1970 at an average rate of -2.1%/year (English et al, 2021a). Rufous hummingbirds occupy diverse habitats over their annual cycle and threats to this species could originate over a broad geographical area: their nonbreeding range encompasses the Mexican plateau, Sierra Madre, and western regions of Mexico (an area of conservation concern; Wilson et al, 2019) as well as the southeastern United States, while their breeding range extends across much of western North America, as far north as coastal southeastern Alaska (Healy and Calder, 2006; Moran et al, 2013; Fink et al, 2020)

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Discussion

Conclusion