RESPONSES OF COASTAL NESTING KING RAILS (RALLUS ELEGANS) TO ENVIRONMENTAL THREATS OF RISING WATER AND TEMPERATURE

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

Amanda J. Clauser (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: King rail (Rallus elegans) populations are experiencing long-term declines attributable to habitat loss. Sparse breeding populations in coastal areas may represent the last strongholds for this species, but climate change models predict these are at risk from extreme weather events, including rising temperatures and higher frequencies and intensities of storms, with associated risks of storm surge and flooding. A breeding population at Mackay Island National Wildlife Refuge (NWR) in coastal North Carolina likely represents an important source population for the region. I investigated the effects of elevated temperatures and rising water on the nesting success of king rails at Mackay Island NWR, and whether they have evolved behavioral plasticity in nesting behavior to mitigate these threats. I further tested the alternative hypothesis that variation among parents in nesting effort may be related to individual differences in body condition. \r\nClutch temperatures that exceed acceptable limits for embryo development may result in embryo mortality. I monitored clutch and ambient temperatures simultaneously using Thermochron iButtons, and I documented parental incubation behavior at king rail nests. Video recordings reveal parents adjust their incubation behavior in response to ambient temperatures, and shading their nest may allow king rails to maintain their clutches below lethal temperatures in hot conditions. However, king rails tend to take more frequent recesses of nest attendance at higher temperatures, exposing their eggs to adverse conditions for embryo development. Clutches that reached higher temperatures for longer periods of time tended to hatch fewer chicks. Additionally, seasonal variation in temperature exposed late season nests to hotter conditions. Parents begin incubating earlier and hatching became more asynchronous later in the breeding season. Although parents show plasticity in incubation behavior, hatching failure related to high clutch temperatures suggests king rails may be constrained in their ability to cope with high temperatures experienced on the nest.\r\nCoastal marsh breeders must also contend with water level variation, and other rails (Family: Rallidae) add material to their nests throughout incubation to prevent nest flooding. Water levels at Mackay Island NWR are influenced by wind-driven tides and, consequently, are exceptionally variable. King rails build taller nests in areas with greater ranges in water levels. Parents spent proportionately more time building when the water level approached the top of the nest. However, individual nest height remained relatively constant and did not increase considerably during the laying period, suggesting that the majority of nest building occurred before laying began. Nest building during the laying and incubation periods may therefore function mainly to counteract settling and improve the structural integrity of the nest. Although they continue to build throughout the nesting cycle, parents may not be able to prevent nest flooding when faced with rapidly rising water.

Additional Information

Publication

Thesis

Language: English

Date: 2023

Subjects

Behavioral plasticity;Shading;Nest flooding;Hatching failure;Incubation temperature

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