Short-finned pilot whales in the South China Sea: Insights into regional distribution,movement pattern,and habitat characteristics

Little scientific knowledge is available for short-finned pilot whales in the South China Sea (SCS). Here, we integrated historical records, ship-based observation, and satellite-tagging data to investigate ecological and behavioral characteristics of pilot whales in the SCS. Historical records since the 1990s showed the widespread spatial occurrence of pilot whales along the coastal SCS, suggesting that the species may inhabit this region. During our dedicated ship-based surveys (2019–2022) in the SCS, 19 groups of pilot whales were encountered in Xisha-Zhongsha waters, which supported the hypothesis inferred from historical data. We believe that Xisha-Zhongsha waters are important habitats for pilot whales, demonstrated by the large group size (M = 44.7 ± 42.4 SD individuals), the high proportion of recorded maternal groups (17/19), mixed-species associations, and deep-water habitat characteristics. During field surveys, we conducted satellite-tagging experiments on two adult pilot whales, with tracking periods of 35 and 13 days, respectively. Satellite-tracking data provided evidence of possible residency of the tagged whales, as both displayed overlapping ranges and nondirectional movement. This research provides preliminary baseline data on occurrence, distribution, movement, habitat use, and likely residency of pilot whales in the SCS, which can facilitate future research and conservation effort.     

PHYSICAL HABITAT OF CETACEANS ALONG THE CONTINENTAL SLOPE IN THE NORTHCENTRAL AND WESTERN GULF OF MEXICO

The physical habitat of cetaceans found along the continental slope in the north-central and western Gulf of Mexico was characterized from shipboard sighting data, simultaneous hydrographic measurements, and satellite remote sensing. The study area was encompassed by the longitude of the Florida-Alabama border (87.5°W), the southernmost latitude of the Texas-Mexico border (26.0°N), and the 100-m and 2,000-m isobaths. Shipboard surveys were conducted seasonally for two years from April 1992 to May 1994. A total of 21,350 km of transect was visually sampled in an area of 154,621 km². Sighting localities of species in the study area were differentiated most clearly with bottom depth. Atlantic spotted dolphins (Stenella frontalis) were consistently found in the shallowest water on the continental shelf and along the shelf break. In addition, the bottom depth gradient (sea floor slope) was less for Atlantic spotted dolphins than for any other species. Bottlenose dolphins (Tursiops truncatus) were found most commonly along the upper slope in water significantly deeper than that for Atlantic spotted dolphins. All the other species and species categories were found over deeper bottom depths; these were Risso's dolphins (Grampus griseus), short-finned pilot whales (Glob-icephala macrorhynchus), pygmy/dwarf sperm whales (Kogia spp.), roughtoothed dolphins (Steno bredanensis), spinner dolphins (Stenella longirostris), sperm whales (Physeter macrocephalus), striped dolphins (Stenella coeruleoalba), Mesoplodon spp., pantropical spotted dolphins (Stenella attenuata), Clymene dolphins (Stenella clymene) and unidentified beaked whales (Ziphiidae). Risso's dolphins and short-finned pilot whales occurred along the upper slope and, as a subgroup, were significantly different from striped dolphins, Mesoplodon spp., pantropical spotted dolphins, Clymene dolphins, and unidentified beaked whales, which occurred in the deepest water. Pygmy/dwarf sperm whales, rough-toothed dolphins, spinner dolphins, and sperm whales occurred at intermediate depths between these two subgroups and overlapped them.     

Wintering Habitat Model for the North Atlantic Right Whale (Eubalaena glacialis) in the Southeastern United States

The coastal waters off the southeastern United States (SEUS) are a primary wintering ground for the endangered North Atlantic right whale (Eubalaena glacialis), used by calving females along with other adult and juvenile whales. Management actions implemented in this area for the recovery of the right whale population rely on accurate habitat characterization and the ability to predict whale distribution over time. We developed a temporally dynamic habitat model to predict wintering right whale distribution in the SEUS using a generalized additive model framework and aerial survey data from 2003/2004 through 2012/2013. We built upon previous habitat models for right whales in the SEUS and include data from new aerial surveys that extend the spatial coverage of the analysis, particularly in the northern portion of this wintering ground. We summarized whale sightings, survey effort corrected for probability of whale detection, and environmental data at a semimonthly resolution. Consistent with previous studies, sea surface temperature (SST), water depth, and survey year were significant predictors of right whale relative abundance. Additionally, distance to shore, distance to the 22°C SST isotherm, and an interaction between time of year and latitude (to account for the latitudinal migration of whales) were also selected in the analysis presented here. Predictions from the model revealed that the location of preferred habitat differs within and between years in correspondence with variation in environmental conditions. Although cow-calf pairs were rarely sighted in the company of other whales, there was minimal evidence that the preferred habitat of cow-calf pairs was different than that of whale groups without calves at the scale of this study. The results of this updated habitat model can be used to inform management decisions for a migratory species in a dynamic oceanic environment.     

NORTH ATLANTIC RIGHT WHALE DISTRIBUTION IN RELATION TO SEA-SURFACE TEMPERATURE IN THE SOUTHEASTERN UNITED STATES CALVING GROUNDS

Standardized aerial surveys were used to document the winter (December–March) distribution of North Atlantic right whales in their calving area off the coasts of Georgia and northeastern Florida (1991–1998). Survey data were collected within four survey zones in and adjacent to federally designated critical habitat. These data, including whale‐sighting locations and sampling effort, were used to describe right whale distribution in relation to sea‐surface temperature (SST) from satellite‐derived images. Locations where whales were sighted (n= 609) had an overall mean SST of 14.3°C ± 2.1° (range 8°–22°C). Data from two survey zones having sufficient data (including the “early warning system” (EWS) zone and the Florida nearshore) were pooled by season and stratified by month to investigate changes in monthly ambient SST and fine‐scale distribution patterns of right whales in relation to SST within spatially explicit search areas. Using Monte Carlo techniques, SSTs and latitudes (means and standard deviations) of locations where whales were sighted were compared to a sampling distribution of each variable derived from daily‐search areas. Overall, results support a nonrandom distribution of right whales in relation to SST: during resident months (January and February), whales exhibited low variability in observed SST and a suggested southward shift in whale distribution toward warmer SSTs in the EWS zone; while in the relatively warmer and southernmost survey zone (Florida nearshore), right whales were concentrated in the northern, cooler portion. Our results support that warm Gulf Stream waters, generally found south and east of delineated critical habitat, represent a thermal limit for right whales and play an important role in their distribution within the calving grounds. These results affirm the inclusion of SST in a multivariate predictive model for right whale distribution in their southeastern habitat.     

Short‐finned pilot whales (Globicephala macrorhynchus) of the Mariana Archipelago: Individual affiliations,movements, and spatial use

Little is known about short‐finned pilot whales (Globicephala macrorhynchus) in the western North Pacific outside of Japanese coastal waters. To expand understanding of short‐finned pilot whale ecology in the region, we conducted small‐boat surveys in 2010?2016 within the Mariana Archipelago to investigate individual associations, movements, spatial use, and dive behavior of short‐finned pilot whales. We collected genetic, photo‐identification, and satellite‐tag data and identified 191 distinctive individuals. A preliminary social network diagram of photo‐cataloged individuals revealed a main cluster that comprised 82% of individuals, representing all five mitochondrial DNA haplotypes identified within the population. Kernel density estimates for tagged short‐finned pilot whales (n = 11) during summer were used to identify areas with the highest probability of use (10% probability density contour), core area (50%) and home range (95%). The area with highest probability of use by short‐finned pilot whales was off the northwest side of Guam. Satellite tag data also suggest that some individuals are island‐associated year‐round. Data from five location‐dive tags demonstrated that the short‐finned pilot whales dove more often to intermediate depths at twilight and night, suggesting they may target prey that forage on the deep scattering layer as it migrates to and from the surface.     

Molecular identification of individual North Atlantic right whales (Eubalaena glacialis) using free-floating feces

During the 1990s, North Atlantic right whales had significantly decreased reproduction and showed signs of compromised health, prompting the initiation of noninvasive fecal-based studies to investigate potential causal factors. The interpretation of these studies is enhanced when the defecator is identified, as data can then be linked to individual life history information. Fecal samples (n= 118) were either collected from single photoidentified whales, associated with several individuals by photoidentification of whales in the vicinity upon sample collection, or were collected when no whales were in the vicinity. Genetic profiles from fecal DNA comprising sex, mitochondrial haplotype, and five microsatellite loci helped assign specific samples to individual right whales based on existing genetic profiles. Profiles were informative in assigning 61 fecal samples to known individuals, 24 of which were collected when no whales were in the vicinity. Whales identified genetically were typically photographed in the same habitat area and on the same day of sample collection (n= 35/48). Twelve profiles new to the genetic database were identified, suggesting fecal sampling provides a means to obtain genetic profiles from previously unsampled individuals, which may help refine estimates of population size and habitat use patterns if annual fecal sampling continues.     

Some like it cold: Temperature‐dependent habitat selection by narwhals

The narwhal (Monodon monoceros) is a high‐Arctic species inhabiting areas that are experiencing increases in sea temperatures, which together with reduction in sea ice are expected to modify the niches of several Arctic marine apex predators. The Scoresby Sound fjord complex in East Greenland is the summer residence for an isolated population of narwhals. The movements of 12 whales instrumented with Fastloc‐GPS transmitters were studied during summer in Scoresby Sound and at their offshore winter ground in 2017–2019. An additional four narwhals provided detailed hydrographic profiles on both summer and winter grounds. Data on diving of the whales were obtained from 20 satellite‐linked time‐depth recorders and 16 Acousonde? recorders that also provided information on the temperature and depth of buzzes. In summer, the foraging whales targeted depths between 300 and 850 m where the preferred areas visited by the whales had temperatures ranging between 0.6 and 1.5°C (mean = 1.1°C, SD = 0.22). The highest probability of buzzing activity during summer was at a temperature of 0.7°C and at depths > 300 m. The whales targeted similar depths at their offshore winter ground where the temperature was slightly higher (range: 0.7–1.7°C, mean = 1.3°C, SD = 0.29). Both the probability of buzzing events and the spatial distribution of the whales in both seasons demonstrated a preferential selection of cold water. This was particularly pronounced in winter where cold coastal water was selected and warm Atlantic water farther offshore was avoided. It is unknown if the small temperature niche of whales while feeding is because prey is concentrated at these temperature gradients and is easier to capture at low temperatures, or because there are limitations in the thermoregulation of the whales. In any case, the small niche requirements together with their strong site fidelity emphasize the sensitivity of narwhals to changes in the thermal characteristics of their habitats.     

The density of odontocete integument depends on blubber lipid composition and temperature

Cetacean integument serves many functional roles, including contribution to whole body buoyancy. The blubber of the integument of different cetacean species contains varying concentrations of triacylglycerols (TAG) and wax esters (WE); generally, these lipid classes have different densities. Integument can also experience a wide range of temperatures during a dive, so its density may change with depth. The goals of this study were to measure integument density and isolated blubber lipid density in three deep‐diving odontocete species (n = 3–4)—short‐finned pilot whales (Globicephala macrorhynchus), pygmy sperm whales (Kogia breviceps), and Gervais' beaked whales (Mesoplodon europeaus)—at different temperatures (6°C–35°C), and to relate these densities to lipid content and composition. Kogia and Mesoplodon integument and isolated lipids had high WE content (78.7–99.5 wt%) and were less dense (by 1.7%–9.3%) than those of Globicephala, which were composed predominately of TAG. Generally, densities increased as temperature decreased. Changes in integument densities mirrored those of isolated lipid densities, suggesting that blubber lipids are largely responsible for the buoyant properties of cetacean integument. These data demonstrate that the contribution of the integument to whole body density depends on lipid class and temperature, and therefore may provide useful, species‐specific correction factors for diving energetics models.     

Depth and temperature associations of haddock Melanogrammus aeglefinus off southern Newfoundland

Using data collected as part of offshore surveys conducted during 1972–2013, haddock Melanogrammus aeglefinus association patterns with depth and temperature in southern Newfoundland waters, the northern extremity of the species' range in the western Atlantic Ocean, were quantified. They were typically concentrated in the deep warm waters along the narrow shelf slope in North‐west Atlantic Fisheries Organization Divisions 3O and 3P with individuals moving seasonally into the shallow waters of the banks as they warmed. While M. aeglefinus were found over a range of depths and temperatures, they were primarily located at depths deeper and temperatures warmer than the median sampled. Analyses demonstrated that of the two hydrographic variables assessed, temperature was most influential in structuring distribution, with individuals appearing to change depth in order to maintain similar temperature throughout the year. Melanogrammus aeglefinus were found predominantly in temperatures of c. 4–8° C which often represented some of the warmest waters available. Differences in fish‐habitat association patterns in relation to sex or maturity status were not readily apparent from the analyses. Warming conditions off Newfoundland and Labrador in recent years might be predicted to improve local M. aeglefinus productivity.     

What Happened to Gray Whales during the Pleistocene? The Ecological Impact of Sea-Level Change on Benthic Feeding Areas in the North Pacific Ocean

Background

Gray whales (Eschrichtius robustus) undertake long migrations, from Baja California to Alaska, to feed on seasonally productive benthos of the Bering and Chukchi seas. The invertebrates that form their primary prey are restricted to shallow water environments, but global sea-level changes during the Pleistocene eliminated or reduced this critical habitat multiple times. Because the fossil record of gray whales is coincident with the onset of Northern Hemisphere glaciation, gray whales survived these massive changes to their feeding habitat, but it is unclear how.

Methodology/Principal Findings

We reconstructed gray whale carrying capacity fluctuations during the past 120,000 years by quantifying gray whale feeding habitat availability using bathymetric data for the North Pacific Ocean, constrained by their maximum diving depth. We calculated carrying capacity based on modern estimates of metabolic demand, prey availability, and feeding duration; we also constrained our estimates to reflect current population size and account for glaciated and non-glaciated areas in the North Pacific. Our results show that key feeding areas eliminated by sea-level lowstands were not replaced by commensurate areas. Our reconstructions show that such reductions affected carrying capacity, and harmonic means of these fluctuations do not differ dramatically from genetic estimates of carrying capacity.

Conclusions/Significance

Assuming current carrying capacity estimates, Pleistocene glacial maxima may have created multiple, weak genetic bottlenecks, although the current temporal resolution of genetic datasets does not test for such signals. Our results do not, however, falsify molecular estimates of pre-whaling population size because those abundances would have been sufficient to survive the loss of major benthic feeding areas (i.e., the majority of the Bering Shelf) during glacial maxima. We propose that gray whales survived the disappearance of their primary feeding ground by employing generalist filter-feeding modes, similar to the resident gray whales found between northern Washington State and Vancouver Island.     

Distribution and abundance of sei whales off the west coast of the Falkland Islands

Little information exists on the current status of Southern Hemisphere sei whales (Balaenoptera borealis). We assessed their distribution and abundance along the west coast of the Falkland Islands (southwest Atlantic) during February and March 2018, using line transect and nonsystematic surveys. Abundance estimates were generated for a single survey stratum using design- and model-based approaches. Sightings of sei whales and unidentified baleen whales (most, if not all, likely to be sei whales) occurred from the coast to the 100 m depth isobath that marked the offshore boundary of the stratum. The modeled distribution predicted highest whale densities in King George Bay and in the waters between Weddell Island and the Passage Islands. Sei whale abundance was estimated as 716 animals (CV = 0.22; 95% CI [448, 1,144]; density = 0.20 whales/km²) using the design-based approach, and 707 animals (CV = 0.11; 95% CI [566, 877]; density = 0.20 whales/km²) using the model-based approach. For sei whales and unidentified baleen whales combined, the equivalent estimates were 916 animals (CV = 0.19; 95% CI [606, 1,384]; density = 0.26 whales/km²) and 895 animals (CV = 0.074; 95% CI [777, 1,032]; density = 0.25 whales/km²). The data indicate that the Falkland Islands inner shelf region may support globally important seasonal feeding aggregations of sei whales, and potentially qualify as a Key Biodiversity Area.     

Evidence of two subaggregations of humpback whales on the Kodiak,Alaska, feeding ground revealed from stable isotope analysis

Knowledge of humpback whale (Megaptera novaeangliae) foraging on feeding grounds is becoming increasingly important as the growing North Pacific population recovers from commercial whaling and consumes more prey, including economically important fishes. We explored spatial and temporal (interannual, within‐season) variability in summer foraging by humpback whales along the eastern side of the Kodiak Archipelago as described by stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios of humpback whale skin (n = 118; 2004–2013). The trophic level (TL) of individual whales was calculated using basal food web δ¹⁵N values collected within the study area. We found evidence for the existence of two subaggregations of humpback whales (“North,” “South”) on the feeding ground that fed at different TLs throughout the study period. Linear mixed models suggest that within an average year, Kodiak humpback whales forage at a consistent TL during the feeding season. TL estimates support mixed consumption of fish and zooplankton species in the “North” (mean ± SE; 3.3 ± 0.1) and predominant foraging on zooplankton in the “South” (3.0 ± 0.1). This trend appears to reflect spatial differences in prey availability, and thus, our results suggest North Pacific humpback whales may segregate on feeding aggregations and target discrete prey species.     

Local adaptation of a Drosophila parasitoid: habitat‐specific differences in thermal reaction norms

Local climate is an important source of selection on thermal reaction norms that has been well investigated in cline studies, where populations sampled along altitudinal or latitudinal gradients are compared. Several biotic factors vary with climate, but are rarely integrated as alternative agents of selection to climatic factors. We tested the hypothesis that habitat may select for thermal reaction norms and magnitude of phenotypic plasticity in a drosophila parasitoid, independently of the climate of origin. We sampled populations of Leptopilina boulardi, a Drosophila parasitoid in two different habitats, orchards and forests. Orchards offer laying opportunities over small distances for parasitoids, with a low variability in the number of hosts per patch, while forests offer more dispersed and more variable patches. The sampling was realized in a temperate and a Mediterranean climate. We measured egg load, volume of eggs, longevity and lipid content for parasitoids reared at two temperatures. Reaction norms were opposite for populations from forests and orchards for investment in reproduction, independently of the climate of origin. The maximal investment of resources in reproduction occurred at the lower temperature in orchards and the higher temperature in forests. Host distribution differences between habitats may explain these opposite reaction norms. We also observed a flatter reaction norm for egg load in forests than in orchards. This relative canalization may have been selected in response to the higher variability in laying opportunities observed in forests. Our results demonstrate the potential role of resource distribution in evolution of thermal plasticity.     

Improving population estimates by quantifying diving and surfacing patterns: A dugong example

Diving animals are available for detection from above the water when environmental conditions are favorable and the animals are near the surface. The number of animals that are unavailable for detection needs to be estimated to obtain unbiased population estimates. The current availability correction factors used in aerial surveys for the dugong (Dugong dugon) allow for variation in environmental conditions but use the average time dugongs spend near the surface (i.e., constant availability corrections). To improve availability estimates, we examined location and dive data from nine dugongs fitted with satellite telemetry units and time‐depth recorders (TDRs) in eastern Australia. The effects of water depth, tidal conditions, and habitat types on dugong surfacing time were examined using generalized linear mixed models (GLMMs). We found that availability for detection differed with water depth, and depth‐specific availability estimates were often lower than the constant estimates. The habitat effect was less influential, and there was no tidal effect. The number of dugongs estimated using depth‐specific availabilities were higher than those obtained using constant availabilities across water depth. Hence, information on water depth can refine availability estimates and subsequent abundance estimates from dugong aerial surveys. The methodology may be applicable to other aquatic wildlife.     

THERMAL INFRARED RADIATION FROM FREE LIVING WHALES

As part of a search for new detection techniques, and for obtaining information on whale surface temperatures, an Agema Thermovision 880 thermal imaging system was used to detect thermal infrared radiation from whales. The study took place along the northern coast of Norway and the northwest coast of Svalbard (68° to 80° N latitude). The emphasis of the study was on minke whales, but humpback, fin, blue and sperm whales were also observed. The apparent radiation temperature was strongly dependent on sea conditions, signal angle, and atmospheric interference; detection depended thus upon weather. During the study, sea surface temperatures varied as much as 7°C but the sea and minke whale body trunk surfaces were usually within 0.0° to 0.1°C of each other. The other species observed had temperature differences of 0.0° to 1.0°C relative to the sea surface. Temperature differences between sea water and whale appendages ranged from 0.0° to 6.0°C. The indicated maximum difference between sea water and blow (i.e., expired air) was 4.0°;C, while the maximum difference for the blowhole was 4.1°C. The results from all whales observed support the belief that the main body trunk is normally not a heat window, this function being reserved for the appendages. However, the results also indicate a regulated dermal blood flow determining heat loss from the body trunk. Detection of whales by thermal infrared radiation from the body trunk appears unreliable; in contrast, the blow and blowhole provided a consistent positive signal with apparent temperature differences to the surroundings ranging from 0.2° to 4.1°C.     

Geographical differences in habitat relationships of cetaceans across an ocean basin

The distributions of highly mobile marine species such as cetaceans are increasingly modeled at basin scale by combining data from multiple regions. However, these basin-wide models often overlook geographical variations in species habitat relationships between regions. We tested for geographical variations in habitat relationships for a suite of cetacean taxa between the two sides of the North Atlantic basin. Using cetacean visual survey data and remote sensing data from the western and eastern basin in summer, we related the probability of presence of twelve cetacean taxa from three guilds to seafloor depth, sea surface temperature and primary productivity. In a generalized additive model framework, we fitted 1) basin-wide (BW) models, assuming a single global relationship, 2) region-specific intercepts (RI) models, assuming relationships with the same shape in both regions, but allowing a region-specific intercept and 3) region-specific shape (RS) models, assuming relationships with different shapes between regions. RS models mostly yielded significantly better fits than BW models, indicating cetacean occurrences were better modeled with region-specific than with global relationships. The better fits of RS models over RI models further provided statistical evidence for differences in the shapes of region-specific relationships. Baleen whales showed striking differences in both the shapes of relationships and their mean presence probabilities between regions. Deep diving whales and delphinoids showed contrasting relationships between regions with few exceptions (e.g. non-statistically different shapes of region-specific relationships for harbor porpoise and beaked whales with depth). Our findings stress the need to account for geographical differences in habitat relationships between regions when modeling species distributions from combined data at the basin scale. Our proposed hypotheses offer a roadmap for understanding why habitat relationships may geographically vary in cetaceans and other highly mobile marine species.     

Calling under pressure: short-finned pilot whales make social calls during deep foraging dives

Toothed whales rely on sound to echolocate prey and communicate with conspecifics, but little is known about how extreme pressure affects pneumatic sound production in deep-diving species with a limited air supply. The short-finned pilot whale (Globicephala macrorhynchus) is a highly social species among the deep-diving toothed whales, in which individuals socialize at the surface but leave their social group in pursuit of prey at depths of up to 1000 m. To investigate if these animals communicate acoustically at depth and test whether hydrostatic pressure affects communication signals, acoustic DTAGs logging sound, depth and orientation were attached to 12 pilot whales. Tagged whales produced tonal calls during deep foraging dives at depths of up to 800 m. Mean call output and duration decreased with depth despite the increased distance to conspecifics at the surface. This shows that the energy content of calls is lower at depths where lungs are collapsed and where the air volume available for sound generation is limited by ambient pressure. Frequency content was unaffected, providing a possible cue for group or species identification of diving whales. Social calls may be important to maintain social ties for foraging animals, but may be impacted adversely by vessel noise.     

Digging in the deep: killer whales' advanced hunting tactic

We document one of the most spectacular predator-prey interactions observed in a marine ecosystem, in which groups of killer whales force tens of tons of herrring out of their safe deep-water habitat to the surface where the whales are superior. Killer whales performing this hunting tactic congregate in large groups, dive to the limit of their capacity, lift herring vertically more than 150 m by coordinated action, and split large aggregations of fish into small, dense schools before attacking them.     

Local distribution and thermal ecology of two intertidal fishes

Geographic variability in the physiological attributes of widely distributed species can be a result of phenotypic plasticity or can reflect evolutionary responses to a particular habitat. In the field, we assessed thermal variability in low and high intertidal pools and the distribution of resident fish species Scartichthys viridis and transitory Girella laevifrons along this vertical intertidal gradient at three localities along the Chilean coast: Antofagasta (the northernmost and warmest habitat), Carrizal Bajo (central coast) and Las Cruces (the southernmost and coldest habitat). In the laboratory, we evaluated the thermal sensitivity of fish captured from each locality. The response to temperature was estimated as the frequency of opercular movements and as thermal selectivity in a gradient; the former being a indirect indicator of energy costs in a particular environment and the latter revealing differential occupation of habitat. Seawater temperature in intertidal pools was greatest at Antofagasta, and within each site was greatest in high intertidal pools. The two intertidal fish species showed opposite patterns of local distribution, with S. viridis primarily inhabiting the lower sectors of the intertidal zone, and G. laevifrons occupying the higher sectors of the intertidal zone. This pattern was consistent for all three localities. Locality was found to be a very important factor determining the frequency of opercular movement and thermal selectivity of both S. viridis and G. laevifrons. Our results suggest that S. viridis and G. laevifrons respond according to: (1) the thermal history of the habitat from which they came, and (2) the immediate physical conditions of their habitat. These results suggest local adaptation rather than plasticity in thermoregulatory and energetic mechanisms.     

Demographic responses of eastern bluebirds to climatic variability in northeastern Arkansas

As climate change continues to alter temperature and precipitation patterns, numerous species have declined. However, populations of some species that show responses to climate change, such as eastern bluebirds (Sialia sialis), have increased or remained stable nationwide. To understand how species are adapting to climate change, we estimated demographic parameters and their responses to climatic variability, using nesting and banding-recapture data between 2003 and 2018 in a northeastern Arkansas eastern bluebird population. Increasing variability in precipitation in the nonbreeding season negatively affected hatchability. Hatching success was negatively affected by increasing variability in maximum temperatures and the number of hot days during the breeding season, but positively affected by increasing winter snow depth. Adult survival was positively affected by increasing snow depth and variability in the number of hot days during the breeding season, but negatively affected by increasing variability in nonbreeding season temperatures. Our results demonstrate that for this study population, annual breeding parameters, though canalized against interannual environmental variation, were affected by seasonal climatic variability. Although climate change may benefit bluebird survival due to increasing variability in winter temperatures and the number of hot days, climatic variability negatively affected breeding parameters and is expected to increase. Because breeding parameters are typically the drivers of population growth rate in short-lived species, these results raise concern for the future of this population of eastern bluebirds.