Habitat selection and foraging site fidelity in Caspian Terns (Hydroprogne caspia) breeding in the Baltic Sea

Habitat preferences and foraging strategies affect population-level space use and are therefore crucial to understanding population change and implementing spatial conservation and management actions. We investigated the breeding season habitat preference and foraging site fidelity of the under-studied and threatened, Baltic Sea population of Caspian Terns (Hydroprogne caspia). Using GPS devices, we tracked 20 adult individuals at two breeding colonies, in Sweden and Finland, from late incubation through chick-rearing. Analyzing foraging movements during this period, we describe trip characteristics for each colony, daily metrics of effort, habitat use, and foraging site fidelity. We found that daily time spent away from the colony increased throughout the season, with colony-level differences in terms of distance travelled per day. In general, terns selected shallow waters between 0–5 meters in depth with certain individuals using inland lakes for foraging. We show, for the first time, that individual Caspian Terns are faithful to foraging sites throughout the breeding season, and that individuals are highly repeatable in their strategies regarding foraging site fidelity. These results fill important knowledge gaps for this at-risk population, and extend our general knowledge of the breeding season foraging ecology of this widespread species.

Interclutch variability in egg characteristics in two species of rail: Is maternal identity encoded in eggshell patterns?

Maternal signatures are present in the eggs of some birds, but quantifying interclutch variability within populations remains challenging. Maternal assignment of eggs with distinctive appearances could be used to non-invasively identify renesting females, including hens returning among years, as well as to identify cases of conspecific brood parasitism. We explored whether King Rail (Rallus elegans) eggs with shared maternity could be matched based on eggshell pattern. We used NaturePatternMatch (NPM) software to match egg images taken in the field in conjunction with spatial and temporal data on nests. Since we had only a small number of marked breeders, we analyzed similar clutch images from a study of Eurasian Common Moorhens (Gallinula chloropus chloropus) with color-banded breeders for which parentage at many nests had been verified genetically to validate the method. We ran 66 King Rail clutches (n = 338 eggs) and 58 Common Moorhen clutches (n = 364 eggs) through NPM. We performed non-metric multidimensional scaling and permutational analysis of variance using the best egg match output from NPM. We also explored whether eggs could be grouped by clutch using a combination of egg dimensions and pattern data derived from NPM using linear discriminant analyses. We then scrutinized specific matches returned by NPM for King Rail eggs to determine whether multiple matches between the same clutches might reveal maternity among nests and inform our understanding of female laying behavior. To do this, we ran separate NPM analyses for clutches photographed over several years from two spatially distant parts of the site. With these narrower datasets, we were able to identify four instances where hens likely returned to breed among years, four likely cases of conspecific brood parasitism, and a within-season re-nesting attempt. Thus, the matching output was helpful in identifying congruent egg patterns among clutches when used in conjunction with spatial and temporal data, revealing previously unrecognized site fidelity, within-season movements, and reproductive interference by breeding females. Egg pattern data in combination with nest mapping can be used to inform our understanding of female reproductive effort, success, and longevity in King Rails. These methods may also be applied to other secretive birds and species of conservation concern.

Ranging Patterns and Site Fidelity of Snubfin Dolphins in Yawuru Nagulagun/Roebuck Bay, Western Australia

For long-lived species such as marine mammals, having sufficient data on ranging patterns and space use in a timescale suitable for population management and conservation can be difficult. Yawuru Nagulagun/Roebuck Bay in the northwest of Western Australia supports one of the largest known populations of Australian snubfin dolphins (Orcaella heinsohni)—a species with a limited distribution, vulnerable conservation status, and high cultural value. Understanding the species’ use of this area will inform management for the long-term conservation of this species. We combined 11 years of data collected from a variety of sources between 2007 and 2020 to assess the ranging patterns and site fidelity of this population. Ranging patterns were estimated using minimum convex polygons (MCPs) and fixed kernel densities (weighted to account for survey effort) to estimate core and representative areas of use for both the population and for individuals. We estimated the population to range over a small area within the bay (103.05 km2). The Mean individual representative area of use (95% Kernel density contour) was estimated as 39.88 km2 (± 32.65 SD) and the Mean individual core area of use (50% Kernel density contour) was estimated as 21.66 km2 (±18.85 SD) with the majority of sightings located in the northern part of the bay less than 10 km from the coastline. Most individuals (56%) showed moderate to high levels of site fidelity (i.e., part-time or long-term residency) when individual re-sight rates were classified using agglomerative hierarchical clustering (AHC). These results emphasize the importance of the area to this vulnerable species, particularly the area within the Port of Broome that has been identified within the population’s core range. The pressures associated with coastal development and exposure to vessel traffic, noise, and humans will need to be considered in ongoing management efforts. Analyzing datasets from multiple studies and across time could be beneficial for threatened species where little is known on their ranging patterns and site fidelity. Combined datasets can provide larger sample sizes over an extended period of time, fill knowledge gaps, highlight data limitations, and identify future research needs to be considered with dedicated studies.

Long distance homing in the cane toad (Rhinella marina) in its native range

Many animals exhibit complex navigation over different scales and environments. Navigation studies in amphibians have largely focused on species with life histories that require accurate spatial movements, such as territorial poison frogs and migratory pond-breeding amphibians that show fidelity to mating sites. However, other amphibian species have remained relatively understudied, leaving open the possibility that well-developed navigational abilities are widespread. Here, we measured short-term space use in non-territorial, non-migratory cane toads (Rhinella marina) in their native range in French Guiana. After establishing site fidelity, we tested their ability to return home following translocations of 500 and 1000 meters. Toads were able to travel in straight trajectories back to home areas, suggesting navigational abilities similar to those observed in amphibians with more complex spatial behavior. These observations break with the current paradigm of amphibian navigation and suggest that navigational abilities may be widely shared among amphibians.

Understanding spatial and temporal patterns in movement and habitat use of black-tailed deer in Northern California, USA

<p>Black-tailed deer (BTD, Odocoileus hemionus columbianus), a socio-economically important deer species in western North America is steadily declining throughout much of its range over the last century. Though a large number of studies have been carried out on forage availability, predation pressure, and population dynamics of the species, there still remain broad gaps in current understanding of the underlying causes, mechanisms, and spatio-temporal patterns of habitat use which can affect the population dynamics and distribution of BTD. So, the central aim of my thesis was to identify the spatial and temporal scale that may affect habitat selection, movement and ultimately long-term persistence of the BTD population in the Mendocino National Forest, California. Understanding population structuring in BTD is vital to underpin the spatial scale for conservation. So, I tested for presence of population sub-structuring among female BTD in the study area by analysing the combined effect of site fidelity and philopatry on the population. Fidelity analyses from radio-telemetry data revealed BTD to have extremely small seasonal home ranges (0.71 km²) and very high site fidelity to these ranges. Direct fitness benefits of fidelity were observed as individuals with decreased site fidelity to their ranges suffered elevated risks of mortality. Results from mtDNA sequencing revealed high genetic differentiation (FST > 0.30) and low haplotype sharing even among geographic areas separated by as little as 4–10 km. Combined, the results indicated prolonged period of philopatric behaviour resulting in demographic isolation and very small scale population sub-structuring that can impact the population dynamics at a finer spatial scale than previously assumed. Next, I examined the effect of temporal scale on resource selection by BTD, through comparing habitat characteristics selected by BTD from a pooled model (all telemetry locations pooled across activity states) versus habitat characteristics associated with foraging (active state) and resting or ruminating (inactive state). The main factors that influenced resource selection in BTD were: 1) seasonal changes associated largely with variable selection towards slope, aspect, and elevation and 2) activity states influenced fine-scale selection towards vegetation type, edge density, and cover within the home-ranges. The comparative analysis also revealed that due to larger proportion of resting and ruminating locations, the pooled model frequently failed to identify critical foraging habitats and reflected habitats associated with resting. The frequent misidentification for important ecological covariates associated with foraging was a testimony that pooling data across activity states in BTD can negatively impact our understanding about habitat selection by the species. Finally, I developed a movement model to understand the spatial and temporal patterns of risk-forage trade-offs by female BTD as a function of landscape familiarity. The results showed that familiarity affects the trade-off patterns by BTD in a heterogeneous landscape, with differential selection towards productivity and risk that also varied largely with habitat types. The results further revealed strong selection towards highly familiar areas by BTD during the night time and at dawn while stepping into less familiar areas during the daytime. The demonstrated preference for familiar locations within their home ranges when their primary predator (puma) is most active emphasizes that spatial familiarity is important not only for large scale processes like selection of home range, but also for striking fine-scale trade-offs between forage and risk within individual home ranges. The knowledge of this fine scale selection pattern is critical for maintaining habitat heterogeneity at a spatial scale comparable to the size of their home ranges, as they have vital consequences on fitness of BTD that ultimately affects the population dynamics of the species.</p>