First Advisor

Tyler Imfeld


Regis College

Degree Name

MS Environmental Biology

Document Type

Thesis - Open Access

Number of Pages

101 pages


Hybrid zones play notable roles in ecological and evolutionary processes and can be impacted by environmental and anthropogenic factors. Increased anthropogenic disturbance is expected to spatially shift these zones and alter hybridization frequencies in many avian taxa, including the red- and yellow-shafted Northern Flickers. These taxa have low levels of genomic divergence and distinct plumage characteristics that vary between red-shafted, yellow-shafted, and hybrid individuals, allowing hybrids to be effectively scored genetically or morphologically. The Flicker hybrid zone has been extensively studied across the Great Plains from a historical and contemporary perspective, however, urbanization and human influences on Flicker hybridization are unknown. Our study evaluated how hybridization frequencies and dynamics of the flicker hybrid zone have changed in the last century along the Colorado Front Range. We quantified historical hybridization by scoring plumage characteristics using existing scoring methods from study skins and assessed this hybrid zone's spatial and temporal dynamics in conjunction with historical land-use data. Using ordination tools, Northern Flickers displayed a major gradient of plumage variation between pure red- and pure yellow-shafted individuals that correlated nearly perfectly with established hybrid index scores. Additionally, we observed nuanced sex biases in major plumage characteristics, where crown coloration covaried with differing plumage characteristics between sexes on the next greatest axis of variation. Hybridization frequency and plumage dynamics did not significantly change over time or in response to increased urbanization in the Colorado Front Range. Our study demonstrates that anthropogenic habitat conversion has not notably altered the Northern Flicker hybrid zone since the late 1800s, emphasizing the long-term stability of hybridization in this region.

Date of Award

Spring 2023

Location (Creation)

Colorado (state); Denver (county); Denver (inhabited place)

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