Long‐term demography of the Northern Goshawk in a variable environment

• Published in: Wildlife Monographs
• Main Authors: Reynolds, Richard T., Lambert, Jeffrey S., Flather, Curtis H., White, Gary C., Bird, Benjamin J., Baggett, L. Scott, Lambert, Carrie, Bayard De Volo, Shelley
• Other Authors: USDA Forest Service Southwestern Region, Rocky Mountain Research Station, North Kaibab Ranger District
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2017
• Subjects: Accipiter gentilis; Northern Goshawk
• Online Access: http://dx.doi.org/10.1002/wmon.1023; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fwmon.1023; https://onlinelibrary.wiley.com/doi/full/10.1002/wmon.1023

ABSTRACT The Nearctic northern goshawk ( Accipiter gentilis atricapillis ) is a resident of conifer, broadleaf, and mixed forests from the boreal to the southwestern montane regions of North America. We report on a 20‐year mark‐recapture investigation (1991–2010) of the distribution and density of breeders, temporal and spatial variability in breeding, nestling sex ratios, local versus immigrant recruitment of breeders, breeding age structure, age‐specific survival rates, and rate of population change (λ) of this species on the Kaibab Plateau, a forested sky island in northern Arizona, USA. We used an information‐theoretic approach to rank models representing alternative hypotheses about the influence of annual fluctuations in precipitation on the annual frequency of goshawk breeding and fledgling production. We studied 125 goshawk breeding territories, representing approximately 87% of an estimated 144 total territories based on a mean distance of 3.8 km between territory centers in a 1,728‐km 2 study area. The salient demographic feature of the population was extensive annual variation in breeding, which manifested as large inter‐annual variation in proportions of pairs laying eggs, brood sizes, nest failure rates, and fledgling production. The percent of territories known in a prior year in which eggs were laid in a current year ranged from 8% to 86% ( = 37%, SE = 4.51), annual mean nest failure rate (active nests that failed) ranged from 12% to 48% (overall = 23%, SE = 2.48), and mean annual brood size of successful nests (fledged ≥1 fledgling) ranged from 1.5 young to 2.5 young (overall = 2.0 young, SE = 0.03). Inter‐annual variation in reproduction closely tracked inter‐annual variation in precipitation, which we hypothesize influenced primary forest productivity and bird and mammal prey abundance. The best breeding years (1992–1993, 77–87% of pairs laid eggs) were coincident with a record‐long El Niño‐Southern Oscillation (ENSO) wet period and the worst breeding year (2003; 8% of pairs laid eggs) was the ...