Date of Award
Doctor of Philosophy (PhD)
I studied brood parasitism and breeding ecology of canvasbacks (Aythya valisineria) and redheads (A. americana) nesting on the Delta Marsh near Portage la Prairie, Manitoba, from 1977 to 1980. The dissertation focuses on 3 aspects of this investigation: 1) the role of prairie drought in influencing pochard reproductive performance, including a comprehensive review of hypotheses explaining evolution of brood parasitism in waterfowl (Anatidae), 2) behavioral ecology and evolution of host/parasite interactions, and 3) development of improved redhead aging techniques by using cluster analysis.
Redheads shifted egg distributions from eggs in redhead nests to eggs laid parasitically in canvasback nests during severe prairie-wide droughts. Furthermore, prairie droughts corresponded with: 1) apparently lower available food resources, 2) lower breeding season body weights, 3) lower attentiveness by incubating redheads, 4) greater spontaneous nest desertion, 5) higher emigration and nonbreeding, and 6) higher egg losses to predators. I characterize redhead parasitism as a bet-hedging reproductive strategy countering high risks, high reproductive costs, and low probability of payoffs for females breeding under less favorable environmental conditions.
Host/parasite interactions of canvasbacks and redheads were explored in detail by remote, time-lapse photography of nesting females. Parasitic females did not appear to encounter major difficulty in locating host nests or depositing parasitic eggs. Individually marked females appeared to follow a bet-hedging egg dispersion strategy. Hosts attempted to avoid being parasitized through various kinds of essentially passive aggression. Several ecological/environmental factors important to waterfowl reproduction may result in evolutionary conflicts and restrict agreement with expectations of optimal evolutionary responses by hosts and parasites.
Feather characters and measurements from fall-collected wings and pen-reared birds frequently differed from those collected from wild redheads in spring. Cluster analyses placed yearling and adult redheads captured in spring into appropriate age groups with an apparent error rate of 1.1% for females and <1% for males. Recommendations are given for alternative statistical approaches to develop waterfowl aging techniques based on structural and character measurements.
Sayler, Rodney D., "Brood Parasitism and Reproduction of Canvasbacks and Redheads on the Delta Marsh" (1985). Theses and Dissertations. 3252.