Herons

I used empirical data to inform spatially- and temporally-explicit predictions of time-integrated habitat availability (TiHAB), quantify spatiotemporal patterns of resource selection by Little Blue Herons (Egretta caerulea), and evaluate foraging activity as function of resource availability and prey dynamics. Evaluating resource availability over time accounts for the magnitude and duration of resource change. This approach is useful for understanding mechanisms that underlie resource selection in dynamic environments and for guilds that are sensitive to changes in prey availability like wading birds. I found that average TiHAB varied interannually whereby gains and losses in Little Blue Heron foraging habitat at the landscape scale (1-8 km) occurred from slight differences in annual tidal cycles otherwise imperceptible with water depth data alone. Local patterns of resource selection by Little Blue Herons were temporally consistent but spatially variable across tidally influenced environments. TiHAB was the most important habitat attribute over time and space and was superior to other environmental features and prey density as a predictor of Little Blue Heron resource selection. Foraging activity did not show a clear association with probability of resource selection, but foraging metrics were best described by changes in TiHAB consistent with changes in foraging strategy. I conclude that spatiotemporal variation in resource availability reliably predicts patterns of dynamic habitat selection and supports an energy-maximizing foraging strategy for wading birds in tidally influenced habitats. This modeling framework can be applied to quantify the spatiotemporal availability of resources in real-time or under hydrologic restoration regimes and sea level rise scenarios, and track species responses to hydrologic and other environmental fluctuations.

Little Blue Herons, Snowy Egrets, and Tricolored Herons that nest in the
Everglades have declined sharply over the past decade, due in part to food resource
limitations. Here, I examined the diet of small herons to determine how prey
characteristics affected the fitness of small herons in the highly modified Florida
Everglades. Analysis of these diet differences showed birds nesting in 2017, a
hydrologically dryer-than average year, and a more taxonomically varied diet were
associated with nest success and improved body condition of nestlings. Over half (51%)
of the fish biomass Little Blue Herons consumed were non-native species, compared to
14% and 19% non-native fish biomass consumed by Snowy Egrets and Tricolored
Herons, respectively. Surprisingly, <7% of fish biomass available in the Everglades were
comprised of non-native fish species, suggesting that small herons, and Little Blue
Herons in particular, may be using alternative foraging habitats, to supplement their
dietary needs.