Date of Award

January 2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Susan N. Ellis-Felege

Abstract

Federally protected interior Least Terns (Sternula antillarum athalassos) and Piping Plovers (Charadrius melodus) are small shorebirds that nest on un-vegetated sand habitat, such as temporary sandbars and permanent islands along inland river systems in the United States including the Missouri River, during the summer months. Extensive monitoring and research has been conducted on the Missouri River populations because they are an important component of recovery efforts for both species; therefore, two of my primary objectives included: 1) estimate rates of and determine factors that influence nest fate misclassifications and 2) evaluate the impacts of research activities on shorebird nesting behaviors and nest predation risk. The examination of possible effects that sand temperatures inflict on avian ground-nesting behavior will be critical to understand in order to adapt or develop recovery plans in response to climate change. My third objective was to assess the response of Least Tern and Piping Plover nesting behaviors in response to rising sand temperatures. As suitable breeding habitat continues to decline for both of these species, my final objective was to determine how the densities of these mixed-species colonies influenced their nesting behaviors.

With advancements in size reduction, increased quality and reduced costs of video cameras, it is possible to monitor multiple nests of a population throughout the reproductive season to capture nesting behaviors that are logistically impractical to document otherwise. During the 2013–2015 breeding seasons, I installed miniature surveillance cameras at 65 of 294 Least Tern and 89 of 551 Piping Plover nests under observation on the Missouri River in North Dakota. For both species, there was no significant difference between the daily survival rate for nests monitored with cameras than without cameras (Piping Plovers: χ2 = 3.28, P = 0.05; Least Terns: χ2 < 0.01, P = 0.98). For a 7-day monitoring interval between visits, 45% of nests were partially and 27.5% were fully misclassified, but a more intensive (3-day) monitoring schedule decreased these rates to 20% and 8% respectively. Researchers were also less likely to correctly classify nest fates for Least Terns than for Piping Plovers and as clutch age as well as monitoring interval increased for both species. Factors that influenced misclassification of nest fates included clutch age, monitoring interval, species breeding attributes, and termination date. Furthermore, causes of failure (e.g., predators, weather) as determined from field evidence versus video disagreed for 53.5% of nests. Nest predators identified from video observation included: American Crow (Corvus brachyrhynchos), Black-billed Magpie (Pica hudsonia), Coyotes (Canis latrans), Raccoon (Procyon lotor), Great Horned Owl (Bubo virginianus), Striped Skunk (Mephitis mephitis), Bald Eagle (Haliaeetus leucocephalus) and Red Fox (Vulpes vulpes).

Adults of both species spent more time absent from the nest (Least Tern=39.7% ± 0.023 se, Piping Plover=26.5% ± 0.019 se) when researchers were present at the nest or in the surrounding area compared to one hour directly before (Least Tern=13.0% ± 0.013 se, Piping Plover=10.1% ± 0.01 se) and after (Least Tern=13.0% ± 0.013 se, Piping Plover=12.2% ± 0.012 se) the research activity time period (n = 70 nests, total number pre, during, post research activity time periods = 1,569). Additionally, daily nest attendance was lower on days with research activities (Least Terns=90.7% ± 0.017 se, Piping Plover=90.8% ± 0.012 se) compared to ones with no occurrence (Least Tern=93.2% ± 0.017 se, Piping Plover=91.7% ± 0.013 se). I found predation risk was 4.995 times more likely for a nest with one research activity/day compared to one without exposure to activities (long-term effect). There were little short-term observer effects on the risk of nest predation.

I installed thermocouples in the sand near all 52 Least Tern and 55 Piping Plover camera nests in 2014 and 2015. Nest attendance decreased 1.2 minutes per degree increase in maximum sand temperature. On average, daily nest attendance was greater for Least Terns (97% ± 13.9 se) compared to Piping Plovers (94% ± 14.4 se). The frequency and duration of shading behaviors increased by 0.21 and 0.31 minutes per day per degree increase in maximum sand temperature. Piping Plovers exhibited more and longer shading behaviors (number of daily shades=5.83 ± 3.16 se, duration of daily shades=4.13 minutes ± 2.69 se) compared to Least Terns (number of daily shades=0.46 ± 0.26 se, duration of daily shades=0.33 minutes ± 0.23 se). Sand temperature had less of an influence on the frequency of nest exchanges because these behaviors are also associated with the need of adults to leave the nest to forage throughout the day.

Both species nest in mixed-species colonies and the more aggressive nest defense behaviors of Least Terns may influence the nesting behaviors of Piping Plovers. Therefore, my objective was to evaluate the impact of colonial dynamics on the nest attendance of both species. I used generalized linear mixed models to evaluate the relationship between daily nest attendance and measures of colonial dynamics, including Least Tern and Piping Plover nest densities as well as the distance to the nearest nest of both species. Julian date, clutch age and species were also included as covariates to account for additional factors that influence nest attendance. Least Tern and Piping Plover nest densities as well as distance to the nearest Least Tern nest were the measures of colonial dynamics included in the top four models (along with species, clutch age and Julian date), which accounted for 45.3 % of the model weight (wi). As Least Tern and Piping Plover nest densities increased by each additional nest/hectare, there was a corresponding rise in the daily nest attendance of both species by 0.55 and 0.88 minutes/day respectively. Adults of both species increased their daily nest attendance by 0.031 minutes/day as distance to the nearest Least Tern nest increased by one meter. The influence of Least Tern and Piping Plover heterospecific colonies on the nesting behaviors of both species may have important implications for potential future management decisions, especially as habitat quantity and quality continues to decline. In other words, the predator protection benefits to Piping Plovers nesting in close proximity to Least Tern nests or within colonies may become more important to manage. Therefore, it will be advantageous to determine which species provides a positive or negative influence within the colony.

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