Date of Award

8-1-1983

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

Abstract

The breeding biology and productivity of the Red-necked Grebe (Podiceps grisegena) were studied in Turtle Mountain Provincial Park, Manitoba, during 1980 and 1981. Arrival dates ranged from mid-April to early June. Pre-nesting intervals ranged from 11 o 42 days and averaged about 20 days. Egg-laying commenced in early May and extended until mid-July. The average clutch size (4.95 eggs) was much larger than those found in other studies of the Red-necked Grebe in North America.

Although the nest success rate was low (26.2%), most failed pairs (83.5%) initiated at least 1 replacement clutch, and more than one-half of the observed pairs successfully hatched 1 or more chicks. Predators, primarily the Raccoon (Procyon lotor), were believed responsible for about half of the egg losses. High residue levels of several pesticides, particularly DDE and PCBs, were believed to have contributed to the low nesting success. About one-quarter of the viability-tested eggs during this study were considered inviable. Ratcliffe indices revealed that thin-shelled eggs were produced and several cracked eggs were found.

Average incubation periods calculated during this study (28-29 days) were longer than the 22-23 day incubation period generally recognized in the literature. Hatching occurred throughout June and July. Successful pairs hatched an average of 2.5 young, but raised only 1.9 young to the age of 1 month. High pesticide loads may have contributed to many of the losses that occurred during pre- and post-hatching stages. Later, intraspecific aggression probably contributed to significant differences in individual mortality rates within large and small broods. Because losses during the second month were minimal, Red-necked Grebes during this study fledged 1.8-1.9 young/successful pair or about 0.9 young/breeding pair.

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