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23 July 2021 Golden Eagle dietary shifts following wildfire and shrub loss have negative consequences for nestling survivorship
Julie A. Heath, Michael N. Kochert, Karen Steenhof
Author Affiliations +
Abstract

Wildfires and invasive species have caused widespread changes in western North America's shrub-steppe landscapes. The bottom–up consequences of degraded shrublands on predator ecology and demography remain poorly understood. We used a before–after paired design to study whether Golden Eagle (Aquila chrysaetos) diet and nestling survivorship changed following wildfires in southwestern Idaho, USA. We assessed burn extents from 1981 to 2013 and vegetation changes between 1979 (pre-burn) and 2014 (post-burn) within 3 km of Golden Eagle nesting centroids. We measured the frequency and biomass of individual prey, calculated diet diversity indexes, and monitored nestling survivorship at 15 territories in 1971–1981 and 2014–2015. On average, 0.70 of the area within 3 km of nesting centroids burned between 1981 and 2013, and the mean proportion of unburned shrubland decreased from 0.73 in 1979 to 0.22 in 2014. Diets in post-burn years were more diverse and had a lower proportion of some shrub-associated species, such as black-tailed jackrabbits (Lepus californicus) and mountain cottontails (Sylvilagus nuttallii), and a higher proportion of American Coots (Fulica americana), Mallards (Anas platyrhynchos), Piute ground squirrels (Urocitellus mollis), and Rock Pigeons (Columba livia) compared with pre-burn years. A high proportion of waterfowl represented a novel change in Golden Eagle diets, which are typically dominated by mammalian prey. Nestling survivorship was positively associated with the proportion of black-tailed jackrabbits and negatively associated with the proportion of Rock Pigeons in eagle diets. Rock Pigeons are a vector for Trichomonas gallinae, a disease-causing protozoan lethal to young eagles. Nesting attempts were more likely to fail (all young die) in the post-burn period compared with the pre-burn period. Dietary shifts are a common mechanism for predators to cope with landscape change, but shifts away from preferred prey to disease vectors affect nestling survivorship and could lead to population-level effects on productivity.

LAY SUMMARY

  • Wildfires have led to the conversion of native shrub-steppe vegetation into non-native grasslands in the Great Basin, USA.

  • We studied how diet and nestling survivorship of Golden Eagles, a top avian predator in this ecosystem, responded to landscape change that affected preferred prey populations.

  • The shrubland area around eagle nesting territories decreased after fires and, consequently, the number of cottontails and jackrabbits in eagle diets decreased as the number of birds, such as waterfowl and Rock Pigeons, increased.

  • Nestling survivorship was positively related to the proportion of black-tailed Jackrabbits in the diet and negatively associated with the number of Rock Pigeons. Survivorship tended to be lower in the post-burn period compared with the pre-burn period.

  • Eagles seem resilient to changes in preferred prey populations, except for increased exposure to disease when they foraged on Rock Pigeons.

Published by Oxford University Press for the American Ornithological Society 2021. This work is written by (a) US Government employee(s) and is in the public domain in the US.
Julie A. Heath, Michael N. Kochert, and Karen Steenhof "Golden Eagle dietary shifts following wildfire and shrub loss have negative consequences for nestling survivorship," Ornithological Applications 123(4), 1-14, (23 July 2021). https://doi.org/10.1093/ornithapp/duab034
Received: 5 February 2021; Accepted: 28 May 2021; Published: 23 July 2021
KEYWORDS
Aquila chrysaetos
Aquila chrysaetos
arbusto
black-tailed jackrabbit
Cambio climático
climate change
Columba livia
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