Date of Award:
Doctor of Philosophy (PhD)
Terry A. Messmer
In 1993, to determine if wild-strain mallard releases could be used as a management practice to increase local mallard breeding populations, I released 2,344,4.5- week-old mallard ducklings (1,200 females and 1,144 males) to wetlands on 12,10.4-km2 sites (approximately 200 per site, 100 females, 100 males) in the North Dakota Prairie Pothole Region. I monitored the release sites to determine if any relationship existed between site characteristics and time of release to duckling survival estimates. I conducted breeding pair surveys during 1994 and 1995 on treatment and paired control sites to compare post-release population levels. Lastly, I analyzed return data and habitat use, and conducted behavioral experiments to determine if wild-strain mallards experienced higher mortality rates and if any observed differences could be explained by behavior.
In 1994,1 observed 55 of the nasal saddled ducklings returning as adult fem ale to the release sites. In 1995, only 5 nasal saddled females were observed, both on treatment and control sites. No difference was observed hi breeding pair populations on treatment and control sites in 1994 (P = 0.18) and 1995 (P = 0.59).
Hard-released wild-strain mallard females had lower survival rates than wild (P = 0.01) and modified gentle-release wild-strain females (P = 0.05). Ail wild-strain females were virtually eliminated from the population by year 4. This suggests that these buds may have been more vulnerable to predation and other mortality factors than wild females. Breeding wild and wild-strain mallard females reacted similarly to human approach, but when flushed, wild females flew farther than wild-strain females (P = 0.0002). Wetlands used by wild-strain females differed from wild females during breeding by type (P < 0.0001) and cover (P = 0.0003) classification. Wild-strain females selected larger, more permanent wetlands exhibiting less emergent vegetation than did wild counterparts. These differences may help to explain why wiki-strain mallard releases did not increase local breeding populations. The lack of band recoveries for wild-strain females during the latter years when viewed in the context of the observed behavioral differences suggests that these birds were unable to adapt to conditions in the wild.
Dixon, Charles E., "Evaluation of the Effects of Single Season Wild-Strain Mallard Releases on Local Breeding Population Densities" (2000). All Graduate Theses and Dissertations. 4528.