Research Interests

Plumage Polymorphisms

We are interested in determining the genetic and selection mechanisms that keep a range of plumage morphs in Swainson’s Hawk populations, and why there is an apparent gradation towards darker individuals in the western ends of the Swainson’s Hawk breeding range. 

We are examining differences in survival, reproduction and behavior of Swainson's Hawks to explain how plumages persist over time. Additionally, we are looking at differences in parasite loads, and changes in morph frequencies over time.

We have dubbed some of the preliminary results the “Oedipus complex in Swainson’s Hawks.”  We have evidence that male Swainson’s Hawks choose mates that resemble their mother, while females do not seem to choose a male based on plumage.

From top to Bottom—Light, Intermediate and Dark morph Swainson's hawks

Seasonal Interactions

For migratory species, conservation efforts in North America may be negated if conditions on the wintering grounds are poor. Therefore it is important to understand the influence of wintering grounds on population dynamics observed on the breeding grounds.

On their wintering grounds Swainson’s Hawks can congregate into flocks from tens to tens of thousands of individuals.  We have already determined that survival of the Butte Valley population declined when monocrotophos, a pesticide used to control grasshopper outbreaks, were heavily used in Argentina. These pesticides caused mass mortalities of Swainson's Hawks in the mid-1990's, and was subsequently banned. We will examine how conditions on the wintering grounds affect body condition (i.e. the amount of energetic reserves individuals have). Using feathers grown in Argentina, we can determine how body condition in Argentina affects timing of breeding, territory quality, reproductive output and survival of individuals nesting in Butte Valley. By examining these factors, we hope to determine how strongly conditions or events in Argentina influence the population dynamics we observe in North America.

We hope to correlate body condition with habitat condition and food availability.  We will also use  satellite transmitters to look at migration timing in relation to relative body condition.

Study Aream Migration route and wintering grounds of Swainson's Hawks.