Tara Stehelin | ALES Graduate Seminar

Event details:  A graduate exam seminar is a presentation of the student’s final research project for their degree.

This is an ALES PhD Final Exam Seminar by Tara Stehelin.  This seminar is open to the general public to attend.

Thesis Topic:   Investigating the effects of climate change on the distribution and phenology of

Olive-sided Flycatcher (Contopus cooperi) and Western Wood-Pewee (C. sordidulus) in

northwestern North America.

Seminar Abstract:

Northwestern North America is predicted to have some of the greatest human-caused changes to climate globally, making study of northern-breeding birds imperative to their conservation and management. Long distance migrants and aerial insectivores such as the Olive-sided Flycatcher (Contopus cooperi, OSFL) and the Western Wood-Pewee (C. sordidulus, WEWP) may be impacted disproportionately, due to additional ex situ stressors on their populations such as habitat loss and changes to insect populations. In the western boreal region, climate-mediated contributions to distribution and abundance can be examined somewhat independently of habitat loss. Identification of areas of potential climate macrorefugia is an important step in management of two species that have experienced dramatic population declines over the past half century.

I generated boosted regression tree models to describe abundance and distributing using abundance data from 1049 unique locations in the boreal and hemiboreal zone of northwestern North America between 1992 and 2014 from a comprehensive dataset managed by the Boreal Avian Modelling (BAM) project. Bootstraps randomly selected abundances and absences stratified by number of observations at each site, then built stagewise models from a suite of 37 climate, landcover, topographical and disturbance covariates combining both spatial and spatiotemporal influences. I included species-specific offsets for detectability. Covariates describing vegetation and landcover were very important in describing abundance, followed by climate and topography. Influences of individual covariates were often non-linear and specific to species, but overall described habitat that was forested, mid-elevation, complex topographically, and moderate in temperature, precipitation and length of summer season. Relative habitat associations revealed an importance of open forest types, tundra, wet areas and riparian habitat as well as old burns.

To predict the influence of climate change on distribution, I generated a second set of models with seven climatic covariates from a baseline time period of 1981 – 2010 and two future time periods: 2041-2070 and 2071-2100 under a comparatively high (RCP8.5) and mid-low (RCP4.5) greenhouse gas concentration. I included a small number of baseline landcover and topographical covariates to constrain over-prediction outside of the plausible range. Mean outputs projected to grids revealed high relative abundances in the northwestern terrestrial regions of the study area, especially in riparian areas and mid-high elevation forests. Variation from sampling error was relatively low for all models.

Applying a spatiotemporal gradient approach, I found areas of low climatic suitability (negative bioclimatic velocity) in central and northwestern BC and this velocity became more pronounced with time. Areas of positive bioclimatic velocity occurred in small isolated regions in far western Alaska and south-interior BC (although at a micro-refugium level details were specific to species). Total predicted abundance was initially high and either remained the same or declined between the baseline and future scenarios for OSFL, but increased for WEWP. Similarly, areas of predicted abundance (range filling) declined between the baseline and future scenarios for OSFL (as indicated by more areas of loss than gain), but increased for WEWP, underscoring the importance of planning proactively for future species-specific needs. Most gains in potential distribution were in the far northeastern and northwestern portions of the study area, calling into question the utility of these potential macrorefugia in size and accessibility. Most losses were inland regions in the northern part of the study area (central Alaska and Yukon).

A predicted impact of climate change on communities is one of altered phenology between community members, such as changes to timing of abundance peaks of essential insect prey for birds feeding their young. Data to support this prediction remain scant, especially in North America. Phenological investigation into the abundance and diversity of insect prey as well as breeding events of these two species of aerial insectivore in southern Yukon revealed patterns of possibly declining insect abundance with year between 2013 and 2017, possibly advancing laying dates (earlier) with year, but not earlier arrival dates, a highly variable and possibly declining nesting success with year, and an often high reliance on second nesting attempts. A daily insect abundance index influenced breeding phenology of birds, but overwhelming evidence of phenological asynchrony using GAMMs was not found, in part because insect abundance did not reveal obvious or predictable annual peaks, this in turn possibly because of high insect diversity in the area.

PhD with Dr. Fiona Schmiegelow