Fall bird migration in western North America during a period of heightened wildfire activity

Abstract

Billions of birds annually migrate between breeding and nonbreeding grounds in North America. During fall 2020, there was a series of alarming mass-mortality events of migratory birds across the western United States, with estimates of 100,000 to 1 million birds having perished. One potential culprit behind these die-offs is wildfires, though there has been little research documenting the indirect effects of wildfires on actively migrating birds. We undertook a multi-year assessment of potential impacts that wildfires may have had on fall bird migration over the past decade, with a particular focus on fall 2020, using systematic bird banding data from southeastern Utah. We used a correlative approach to evaluate the relationship between estimates of acres burned by wildfires in western North America on several variables representing bird abundance and body condition. Notably, in our best fit models of birds banded at our research site during fall 2020, we found both a positive relationship for the number of bird captures and a negative relationship for body mass index with more daily burned acres. We provide an examination of incorporating lag effects of wildfires on different metrics of bird migration to account for potential impacts of fires on birds before migration and banding. Additionally, we assess the usefulness of different proxies of body condition in highly stressed land birds and introduce a scale for scoring emaciation of birds in the hand while banding. Our insights into avian migration ecology are one of the few studies that explore the role wildfires may have had in affecting migratory bird movements and health. Migration automnale d'oiseaux dans l'ouest de l'Amérique du Nord en période intense d'incendies de forêtRÉSUMÉ. Des milliards d'oiseaux migrent chaque année entre les aires de nidification et celles en dehors de la saison de nidification en Amérique du Nord. Au cours de l'automne 2020, une série d'évènements alarmants de mortalité massive d'oiseaux migrateurs a eu lieu dans l'ouest des États-Unis, l'estimation d'oiseaux ayant péri oscillant entre 100 000 et 1 million. Les incendies de forêt sont l'un des potentiels responsables de ces mortalités, bien que peu de recherches aient été menées sur les effets indirects de ceux-ci sur les oiseaux en migration active. Nous avons entrepris une évaluation pluriannuelle des impacts potentiels des incendies sur la migration automnale des oiseaux au cours de la dernière décennie, en portant une attention particulière à l'automne 2020, au moyen des données de baguage d'oiseaux dans le sud-est de l'Utah. Nous avons utilisé une approche corrélative pour évaluer la relation entre le nombre d'acres brûlés par les incendies de forêt dans l'ouest de l'Amérique du Nord et plusieurs variables décrivant l'abondance et la condition physique des oiseaux. Fait notable, nos meilleurs modèles, à partir des oiseaux bagués à notre site de recherche au cours de l'automne 2020, ont révélé une relation positive du nombre de captures d'oiseaux et une relation négative de ...

Solar Bird Banding: Notes on Changes in Avian Behavior While Mist-netting During an Eclipse

“…We next assessed the age and sex of individuals (Pyle 2022), examined the body and flight feathers for signs of molt, and then determined the WRP code (Pyle 2022; Pyle et al 2022). We then recorded morphometric information such as fat score, body condition (Kittelberger et al 2022), wing length, and body mass, the latter of which we calculated by weighing a bird on a scale. Lastly, we noted the net-check time at which an individual bird was captured, along with the specific net in which the bird was found.…”

More than mortality: Consequences of human activity on migrating birds extend beyond direct mortality

“…Severe wildfires in 2020 were estimated to kill over 1 million birds in Brazil (Tomas et al 2021) and between 100,000 and 1 million migrating birds in the U.S. (Kittelberger et al 2022). Wildfires can injure or kill birds via burning or smoke inhalation (Sanderfoot and Holloway 2017, Nimmo et al 2021, Sanderfoot et al 2021, Jolly et al 2022).…”

“…Community scientists recently documented a mass avian casualty event coinciding with a period of intense wildfire activity across the western U.S. (Yang et al 2021, Irannezhad et al 2022) where the deaths of migrating passerines were correlated with proximity to both wildfires and poor air quality (Yang et al 2021). Live birds captured during this period showed poor body condition and evidence of emaciation (Kittelberger et al 2022), indicating that fires may have spurred them to migrate before they were ready or interfered with their ability to refuel en route (Yang et al 2021, Irannezhad et al 2022, Kittelberger et al 2022).…”

“…Birds' efforts to circumnavigate smoke plumes increased the distances they traveled, doubling the time they spent on migration (Overton et al 2022). The energetic cost of avoiding wildfires while migrating is probably substantial (Kittelberger et al 2022); Greater White-fronted Geese would need to forage for an additional 4–6 days to compensate for the increased energy expenditure (Overton et al 2022). While geese avoided wildfires, nocturnally migrating passerines are frequently attracted to and disoriented by bright light (see ALAN section above), and might be drawn towards wildfires (Stone 1906, Bjorge 1987).…”