SOURCES OF VARIATION IN WATERFOWL NEST PREDATION
Date
1994
Authors
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ORCID
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Degree Level
Masters
Abstract
Nest loss is an important factor reducing the reproductive success of ground-nesting birds. However, it is unclear why certain nests hatch whereas others are destroyed by predators. Consequently, I performed experiments with conditioned taste aversion and measured
characteristics of natural and simulated duck nests to evaluate clutch survival in relation to: i) avian and mammalian predation; ii) nest location (site, habitat, distance to edges); iii) time; iv) spatial dispersion of nests; and v) vegetative characteristics around nests.
Previous studies have examined the efficacy of conditioned taste aversion (CTA) in reducing egg predation at sites baited with eggs, but not at natural nests. Therefore, I evaluated whether CTA might be generalized, protecting eggs in natural nests of ducks in southcentral Saskatchewan. Consumption of eggs was monitored at baiting sites placed near nests of American Crows and in locations likely to be frequented by mammals. During the treatment period, eggs placed near crow nests contained the illnessĀ inducing compound carbachol, whereas mammals were
exposed to eggs treated with estrogen. Egg consumption decreased or ceased altogether at baiting sites located near crow nests, but not at sites baited for mammals. Hatching success of
natural duck clutches was not higher in sites where either crows, mammals or both were treated; relative duck brood abundance also was not higher on treated sites. Results with simulated clutches were mixed. In 1991, sites treated with carbachol (crows) did not differ from controls. By contrast, in 1992, success was higher in treatments than controls i) early in the year at sites where both crows and mammals were treated and again ii) later that year in all
treatments. Although I followed guidelines established from earlier research, my results provided little support for the notion that CTA is generalized to protect natural nests. Dose rate, egg size, taste and colour, as well as nest odour, are some factors that might have affected these findings. Further information on individual predator species (ecology and response to CTA) may also aid the design of a more effective baiting strategy. Nest site locations that reduce nest predation should be advantageous to individual birds, and sites that enhance survival are characteristics of habitats that might be created as part of habitat restoration schemes. However, it is uncertain whether such sites exist. To examine this, I measured distance to patch edge, wetland edge, nearest crow nest, nearest mammalian bait site, and nearest neighbour for
all natural duck nests. In general, I found no relationship between spatial characteristics, habitat type and nest fate. Besides the spatial characteristics of nest locations, nest site vegetation features may aid in the protection of nests from predators, particularly if these predators are birds. To investigate this, lateral density, overhead concealment, and vegetation height were measured at natural and simulated nests. In addition, an index of avian predator abundance
was calculated. Nest fate was not related to features of nest vegetation, except that successful duck nests had greater overhead concealment. In addition, nest fate was not related to abundance of avian predators. contrary to predicted patterns, the relationship between nest fate and overhead concealment was not stronger on sites where avian predators were most numerous. Natural duck nests had greater lateral cover and taller vegetation than simulated
nests, indicating that results from simulated nests should be accepted cautiously, particularly when these features are related to nest fate.
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Degree
Master of Science (M.Sc.)
Department
Biology
Program
Biology