Susan B. McRae

Introduction: The king rail ( Rallus elegans ) is a secretive, obligate freshwater marsh specialist whose population declines and range contraction are attributed primarily to anthropogenic habitat loss. Remaining populations are concentrated along the coastal margins of its historical range in the eastern half of the United States. We investigated seasonal variation in home range size, movements and habitat use in a resident population occupying wetlands along a tidal river in the South Carolina Lowcountry. In contrast to previous studies of king rail movements in vast coastal marsh complexes, the landscape in this region was a patchwork of managed impoundments, tidal wetlands, mudflats, flooded forest and residential properties; remnants of the historical but long since abandoned commercial rice industry. Methods: We used radiotelemetry to track king rails through this fragmented landscape over two years to determine breeding and non-breeding home ranges. Results: Seasonal home range sizes varied (95% kernel density: 1.2–9.1 ha), but seasonal means were not significantly different. Some were among the smallest home ranges reported for king rails, reflecting high prey densities and population concentration in impounded areas. Heavier males remained in place throughout the year, but lighter males made large home range shifts between breeding and non-breeding periods. Studies across the species range have reported similar home range shifts, though the distances moved were remarkable in this region. We relate the timing and context of shifts to breeding status. Breeding king rails selected microhabitat with a high proportion of marsh vegetation near channels of water. While they avoided woody vegetation during nesting, king rails used wooded wetlands in the non-breeding season. When impoundments were flooded for overwintering waterfowl, king rails moved to adjacent tidal marsh or flooded forest. Discussion: Recent rice cultivation to provide winter forage for waterfowl overlaps the breeding season, and clearing of native vegetation rendered impoundments unsuitable for king rails for several weeks. Leaving strips of unmanipulated emergent vegetation around the perimeter provided important cover during this period. Solutions are offered for minimizing impacts to king rails breeding in rice impoundments.

Captive breeding can be a key component of species conservation strategies, but also exposes these rare species to novel environments including the pathogen landscape. The critically endangered white‐winged wood duck (WWWD) Asarcornis scutulata has experienced substantial population declines, local extirpations and fragmentation of its former range in Southeast Asia, making it one of the rarest birds in the world. As in other rare species, WWWD declines have led to the initiation of captive breeding programs, but these have been hampered by the WWWDs' high susceptibility to Mycobacterium avium , avian tuberculosis (TB). In this study we describe genome‐wide patterns of diversity to understand the WWWD's demographic and phylogeographic history, inbreeding in the wild and in captivity, and the causes of TB susceptibility. Captive birds, which originated from northeast India, are genetically differentiated from wild birds sampled in Sumatra, Indonesia, likely reflecting long‐standing phylogeographic structure. Demographic analyses revealed that long‐term (Pleistocene) population declines preceded anthropogenic declines, a pattern shared with other codistributed, forest‐dependent species. All sampled WWWD populations had extremely low genetic diversity ( π = 0.0008–0.0015) but wild‐sampled birds retained higher Major Histocompatibility Complex (MHC) diversity, reflecting important functional diversity in the wild. Genetic diversity has eroded over time in captivity and importantly, birds with higher levels of inbreeding succumb earlier to TB infections, suggesting inbreeding depression. Finally, by comparing gene expression between susceptible WWWD and resistant redhead ducks Aythya americana we identify possible mechanisms of TB susceptibility. Altogether our study provides genomically‐guided objectives for future management and a cautionary tale for ex situ conservation.

Captive breeding can be a key component of species conservation strategies, but also exposes these rare species to novel environments including the pathogen landscape. The critically endangered white-winged wood duck (WWWD) Asarcornis scutulata has experienced substantial population declines, local extirpations and fragmentation of its former range in South-East Asia, making it one of the rarest birds in the world. Like other rare species, WWWD declines have led to the initiation of captive breeding programs, but these have been hampered by the WWWDs’ high susceptibility to Mycobacterium avium , avian tuberculosis (TB). In this study we describe genome-wide patterns of diversity to understand the WWWD’s demographic and phylogeographic history, inbreeding in the wild and in captivity, and the causes of TB susceptibility. Captive birds, which originated from northeast India, are genetically differentiated from wild birds sampled in Sumatra, Indonesia, likely reflecting long-standing phylogeographic structure. Demographic analyses revealed that long-term (Pleistocene) population declines preceded anthropogenic declines, a pattern shared with other codistributed, forest-dependent species. All sampled WWWD populations had extremely low genetic diversity but wild-sampled birds retained higher Major Histocompatibility Complex (MHC) diversity, reflecting important functional diversity in the wild. Genetic diversity has eroded over time in captivity and importantly, birds with higher levels of inbreeding succumb earlier to TB infections, suggesting inbreeding depression. Finally, by comparing gene expression between susceptible WWWD and resistant redhead ducks Aythya americana we identify possible mechanisms of TB susceptibility in WWWD. Altogether our study provides genomically-guided objectives for future management and a cautionary tale for ex-situ conservation.

Coastal ecosystems across the globe are threatened due to anthropogenic activities and human-mediated climate change. Sea level rise and altered hydrology may lead to increased secondary contact between closely related freshwater and saltwater species, such as Rallus elegans (King Rail) and R. crepitans (Clapper Rail). The 2 rallid species are secretive marsh birds with declining populations and largely uncharacterized population structure. Rallus elegans and R. crepitans are known to hybridize, but the extent of hybridization and introgression have not been studied using modern genomics. Hence, to increase our understanding of the connectivity of R. crepitans populations and their hybridization with R. elegans, we adopted a genomic approach using restriction site-associated DNA sequencing (RAD-seq) to examine intra- and interspecific variation in single nucleotide polymorphisms (SNPs) from populations along the east coast of North America. We obtained 154 R. crepitans samples from Connecticut, Delaware, North Carolina, South Carolina, and Louisiana and 50 R. elegans samples from North Carolina and Louisiana. In addition, we included 15 putative hybrids collected in Louisiana. Using 8,834 SNPs across the genome, we found that some individuals had been misidentified in the field, including 5 cryptic hybrids from Delaware salt marshes classified as R. crepitans and 16 individuals from Louisiana. There was evidence of hybridization across all sampled populations with more than 20% of sampled individuals having some degree of introgression based on 142 SNPs found to be fixed between the parental species. Our results suggest that R. crepitans is panmictic, and we found no support for the currently described subspecies in the sampling regions. The 2 R. elegans populations show some evidence of differentiation, albeit with weak support.

Ecological and social factors shape individual reproductive strategies. Climate change has wide‐ranging effects on the timing of reproduction and availability of nesting sites for many birds. Ecological factors such as season length or predation rate could in turn affect the relative success rates of alternative reproductive tactics (ARTs). A new article by Pöysä (2024) featuring a long‐term study of common goldeneyes Bucephala clangula highlights the role of climate change in altering rates of conspecific brood parasitism (CBP) by affecting nest initiation dates and season length. While some authors have emphasized the effects of spatial and temporal aggregation of nests in promoting tactics of reproductive interference, few studies have addressed the effects of environmental variables on rates of CBP and other ARTs. I review some of the evidence for a relationship between population‐level nest predation rate and rates of CBP, principally in ducks and rails, and suggest a role for high rates of nest loss from all sources in the evolution of CBP and host responses. There is a need for further studies that examine environmental correlates of ARTs. Long‐term studies have the highest potential to reveal how shifts in phenology and life history variables may respond to environmental perturbations. Comparative studies of similar species in remote geographic locations can add perspective of how different ecological variables affect the prevalence of ARTs.

Eggshell pigments are costly to produce. The sexual signaling hypothesis predicts that the degree of pigmentation in eggshells is positively related to maternal quality. Thus, females in better condition are expected to lay brighter or more maculated eggs. To test this, we quantified the extent of maculation in eggshells of King Rails (Rallus elegans) and Common Moorhens (Gallinula chloropus chloropus) and related this to female body condition. We identified key variables for body condition using principal components analysis of morphometric measures. To evaluate which combination of variables provided the best index of body condition in each species, a series of linear models were ranked using AICc. To estimate the area of surface pigment on each egg, color egg images were converted to binary and we calculated the percent of black pixels within a scaled oval superimposed over the images. We ran linear regressions of mean percent pigmentation on maternal body condition. Neither female King Rails nor Common Moorhens in better body condition laid more maculated eggs. Thus, the sexual signaling hypothesis was not supported. Common Moorhen eggs were slightly larger, on average, and their eggshells had more pigment per unit area and per egg than King Rail eggs.

Considerable within-population variation in nest size exists among cavity nesters. We sought to explain this by studying a multi-brooded population of Eastern Bluebirds (Sialia sialis) breeding in nest boxes. We examined seasonal change in nest weights and compared the weights of nests built by immigrant and resident females. We further investigated whether nest weight correlated with maternal condition or breeding success. Nest weight measured after broods fledged was correlated with nest height at the start of incubation. Breeders spent fewer days building and built successively smaller, lighter nests in later nesting attempts. Female bluebirds performed the majority of nest construction. Nests built by immigrant females were significantly larger on average than those built by female recruits hatched on site, and the seasonal decline in nest weight was more pronounced for natally philopatric females. For the first time, we present evidence that the weights of philopatric females’ first nests were significantly positively correlated with the weights of the nests they were raised in, suggesting an effect of natal memory. Contrary to expectation, neither maternal condition nor reproductive success (clutch size, hatching success, brood size, and fledging success) was related to nest weight. To investigate whether smaller nests provided a thermal advantage in summer nest attempts when afternoon box temperatures can exceed 41°C, we measured the temperature within nest boxes using programmable data loggers. Mean daily maximum box temperatures during incubation were significantly positively related to nest weight and significantly negatively related to the volume of free space above the nest. Increased air circulation above the nest likely contributed to cooling the boxes when ambient temperatures were high. Reducing nest size was therefore advantageous, especially in later nesting attempts when ambient temperatures were warmest. Seasonal decline in nest weights and differences between immigrant and natally philopatric females merits further investigation.

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.

Neice, A. A. and S. B. McRae. 2021. Mapping habitat suitability for the Eastern Black Rail throughout its Atlantic coastal range using maximum entropy (MaxEnt). Avian Conservation and Ecology 16(1):23. https://doi.org/10.5751/ACE-01919-160123

Autonomous recording units (ARUs) provide a non‐invasive and efficient method for acoustic detection of elusive species across large temporal and spatial scales. However, species with indistinct vocalization structures can be a considerable challenge for automated signal recognizers. We investigated the performance of ARUs and signal recognizers in identifying the broadband, short‐syllable, pulsed calls of a secretive, threatened marsh bird, the King Rail Rallus elegans. Other sympatric species in the same habitat also have repetitive calls within the same frequency range that can be difficult to distinguish. Following serial ARU deployments at specified sites in known breeding habitat, we conducted standardized callback surveys and nest searches to provide an independent measure of breeder density. To analyse recordings, we developed a signal recognizer based on user‐input training files to detect two common call types, kek and grunt. Detections that remained following manual review of recognizer output revealed a previously undescribed seasonal decline and crepuscular diel pattern in calling rate. The rate of the grunt call also predicted density. These patterns emerged despite the recognizer's low precision and high false‐positive rate, which were largely due to misclassification of other species' calls, although ambient noise and effective detection radius also limited the detectability of King Rail calls. We demonstrate that with informed ARU scheduling, improved ability to manipulate user‐specified parameters within signal detection software, and attention to quality control, even the simplest call structures can be located consistently in a diverse acoustic landscape. Our behavioural findings will inform improvements to auditory surveys and to management of King Rails across their range.