Indirect Effects of Non-Native Fish On the Avian Recipients of a Resource Subsidy

EPA Grant Number: F5F21828
Title: Indirect Effects of Non-Native Fish On the Avian Recipients of a Resource Subsidy
Investigators: Epanchin, Peter N.
Institution: University of California - Davis
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2005 through August 31, 2008
Project Amount: $102,584
RFA: STAR Graduate Fellowships (2005) RFA Text |  Recipients Lists
Research Category: Academic Fellowships


The objective of this research is to quantify the extent to which introduced fish indirectly affect the foraging behavior, nesting behavior, and reproductive success of an alpine bird, as mediated by their competition for aquatic insects.


Non-native fish have been introduced to the majority of naturally-fishless lakes in California’s Sierra Nevada, but their broader ecological impacts are poorly understood. This study examines the role of introduced trout in directly altering the abundance of lake-derived insects and the indirect effects of introduced fish on Gray-crowned Rosy Finch (Leucosticte tephrocotis) populations in a Sierra Nevada alpine ecosystem. To gauge the importance of the indirect effects of non-native fish on finches, this study quantifies the finches’ aggregative and numerical responses to the presence of fish by measuring and comparing:

  1. the abundance of insects and foraging finches at both fish-containing lakes and fishless lakes;
  2. and the reproductive effort and success of birds that receive lake-derived inputs with birds that do not receive these inputs.

Using point-count surveys, I will measure bird abundance at each fishless and fish-containing study lake. The timing of aquatic insect emergence from lakes will be measured using aquatic insect emergence traps. Insects will be preserved, identified, and their biomass will be recorded. Color bands and radio-telemetry will be used to identify individual finches and monitor their nesting and foraging behavior and locations. Nests will be monitored for reproductive output, hatching success, and hatchling development. In addition, body feathers will be collected for stable isotope analysis to determine the importance of each trophic level in the birds’ diet.

Expected Results:

In the 2004 pilot study, large-bodied insects were absent at fish-containing lakes and significantly more finches foraged on emerging aquatic insects at experimentally fishless lakes than at fish-containing lakes. Fishless lakes thus appear to provide a reliable insect prey base that nesting alpine passerines can exploit. I will expand the spatial scale of this study and quantify the numerical responses of finches. I expect the results of my research to demonstrate:

  1. the importance of a lake-derived invertebrate resource to finches breeding in an extreme environment;
  2. and the significance of the indirect effects of non-native fish on the foraging behavior and reproductive output of these bird species.

The ecological contributions of this project include an assessment of the importance of resource subsidies from aquatic systems for birds and an examination of how non-native predators introduced to donor systems alter the trophic structure of recipient systems. In addition, this study offers a relevant model for understanding and managing related systems given that fish have been introduced to many mountain lakes worldwide and may affect other passerines and associated food webs in a similar manner as that outlined here.

Supplemental Keywords:

Resource subsidy, trophic interaction, invasive species, introduced predator, donor system, recipient system, biodiversity, allochthonous resource, alpine lakes, Sierra Nevada,, RFA, Ecosystem Protection/Environmental Exposure & Risk, Monitoring/Modeling, Habitat, habitat dynamics, habitat species co-occurrence, fish, food web, biodiversity, community composition, avian community dynamics, ecological consequences, introduced trout, birds, invasive species, breeding habitat

Progress and Final Reports:

  • 2006
  • 2007
  • Final