Factors affecting lifetime reproduction, long-term territory-specific reproduction, and estimation of habitat quality in northern goshawks

PLoS One. 2019 May 22;14(5):e0215841. doi: 10.1371/journal.pone.0215841. eCollection 2019.

Abstract

One measure of habitat quality is a species' demographic performance in a habitat and the gold standard metric of performance is reproduction. Such a measure, however, may be misleading if individual quality is a fitness determinant. We report on factors affecting lifetime reproduction (LR), the total number of lifetime fledglings produced by an individual, and long-term territory-specific reproduction in a multi-generational study of northern goshawks (Accipiter gentilis). LR increased with longer lifespans and more breeding attempts and was strongly correlated with the number of recruits in two filial generations indicating that LR was a good fitness predictor. Extensive differences in LR attested to heterogeneity in individual quality, a requisite for the ideal pre-emptive distribution model (IPD) of habitat settling wherein high quality individuals get the best habitats forcing lower quality individuals into poorer habitats with lower reproduction. In response to 7‒9-year prey abundance cycles, annual frequency of territory occupancy by breeders was highly variable and low overall with monotonic increases in vacancies through low prey years. Occupancy of territories by breeders differed from random; some appeared preferred while others were avoided, producing a right-skewed distribution of total territory-specific fledgling production. However, mean fledglings per nest attempt was only slightly lower in less versus more productive territories, and, contrary to IPD predictions of increases in annual territory-specific coefficients of variation (CV) in reproduction as breeder densities increase, the CV of production decreased as density increased. Rather than habitat quality per se, conspecific attraction elicited territory selection by prospecting goshawks as 70% of settlers comprised turnovers on territories, resulting in occupancy continuity and increased territory-specific reproduction. Top-producing territories had as few as 2 long-lived (high LR) and up to 6 short-lived (low LR) sequential breeders. While individual quality appeared to effect territory-specific heterogeneity in reproductive performance, our data suggests that differences in individual quality may be washed-out by a random settling of prospectors in response to conspecific attraction.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Birds / physiology*
  • Breeding
  • Ecosystem*
  • Longevity
  • Population Dynamics
  • Predatory Behavior
  • Reproduction*

Grants and funding

This study was funded by the USDA Forest Service Southwestern Region and Rocky Mountain Research Station, Arizona Game and Fish Department, and Joint Fire Science Program. Housing and logistical support was provided by the North Kaibab Ranger District. Other than the Arizona Game and Fish Department, the funders provided support in the form of salaries, logistics, and field equipment, but did not have any role in the study design, data collection, data analysis, decision to publish, or preparation of the manuscript. In addition to support in the form of salaries and field equipment, Arizona Game and Fish Department provided 4 employees to help in data collection in 1992. These employees did not have any role in the study design, data analysis, decision to publish, or preparation of the manuscript.