How Do Daily Survival Rates of Nests Change during the Incubation Period for Ducks Nesting on Great Salt Lake Marshes?

Authors

• Mark E. Bell, Utah State University
• Michael R. Conover, Utah State UniversityFollow

Date of this Version

Spring 2024

Document Type

Article

Citation

Human–Wildlife Interactions (Spring 2024) 18(1): article 6 

doi: 10.26077/y35g-d534

Comments

Open access. License: CC BY 4.0

Abstract

We examined how daily survival rates (DSRs) of duck nests change over the course of the incubation period using cinnamon teal (Spatula cyanoptera), mallards (Anas platyrhynchos), and gadwalls (Mareca strepera) nesting in the marshes around Great Salt Lake, Utah, USA. Cameras observed 138 nests, allowing us to know the exact day when chicks hatched or nests were depredated. We measured the course of the incubation period based on 3 different time scales: (1) days since we first located the nest, (2) embryo age, and (3) ordinal day. We tested 3 hypotheses about the relationship between DSRs and the passage of time. The constant-DSR hypothesis proposed that DSRs were constant across the incubation period. The olfactory-concealment hypothesis argued that DSRs should decline over the incubation period because as embryos become older their odorants and those from the incubating hen will increase, allowing olfactory predators, such as raccoons (Procyon lotor) and striped skunks (Mephitis mephitis), to find nests with greater ease. The optimal-timing hypothesis stated that DSRs will be highest during ordinal days in the middle of the normal incubation period and lower earlier and later. We found that DSRs were constant throughout the incubation period when plotted over the number of days since the nest was discovered and embryo age, discrediting the olfactory-concealment hypothesis. When the incubation was expressed as ordinal days, DSRs showed a quadratic curve with DSRs being highest during the middle of the incubation period and lowest during the early and late part, supporting the optimal-timing hypothesis. Our results show the pattern of DSRs during incubation vary based on which method is used to measure time. Our finding that DSRs were lowest during the early part of the incubation period suggests that efforts to protect duck nests from predators should be concentrated at the beginning of the incubation period.