SHORT COMMUNICATION UNDERWATER SOUND PRODUCTION IN A NEOTROPICAL ANURAN,PHYSALAEMUS PUSTULOSUS (LEPTODACTYLIDAE)

ABSTRACT

Underwater vocalisations of Weddell seals Leptonychotes weddellii were recorded approximately 1400 km apart at Casey and Davis, Antarctica. Recordings were made during the 1992 and 1997 breeding seasons at Davis and during the 1997 season at Casey. Two observers independently analysed four attributes (start and end frequency, duration and number of elements) of narrow bandwidth calls from each location and time. There were few observer differences when the calls were grouped into four broad types (Trills, Descending Whistles, Ascending Whistles and Mews). Ascending Whistles and Mews were rare at Casey but common at Davis. Descending Whistles occurred significantly more often at Davis. Except for Trills, discriminant function analyses indicated less variation between the call attributes at Davis in 1992 and 1997 than between either of the Davis data sets and that from Casey. Vocalisation differences between Weddell seals from different areas can be detected by measuring common attributes of narrow bandwidth calls.     

Variations in underwater vocalizations of Weddell seals (Leptonychotes weddelli) at the Vestfold Hills as a measure of breeding population discreteness

Weddell seal vocalizations from Davis Station showed similarities to those from McMurdo Sound and Palmer Peninsula, but none were identical. One vocalization, DD1, was unique to Davis Station. At all sites trills, or territorial defense calls, were the most common and had more types than other calls. Chugs, an aggressive sound, were common at all sites. Weddell seal calls from Davis Station showed similarities to sounds from McMurdo by sharing the use of prefixes and suffixes. Sounds from Davis Station shared the use of both ascending and descending trills and whistles with calls from Palmer Peninsula.Commonalities in underwater vocalizations may indicate the degree of mixing between breeding populations, in which case, Weddell seals in the Davis area probably are from a breeding population distinct from those at either McMurdo Sound or Palmer Peninsula.     

Contrasting behavior between two populations of an ice‐obligate predator in East Antarctica

The Austral autumn–winter is a critical period for capital breeders such as Weddell seals that must optimize resource acquisition and storage to provision breeding in the subsequent spring. However, how Weddell seals find food in the winter months remains poorly documented. We equipped adult Weddell seals after their annual molt with satellite‐relayed data loggers at two sites in East Antarctica: Dumont D'Urville (n = 12, DDU) and Davis (n = 20). We used binomial generalized mixed‐effect models to investigate Weddell seals’ behavioral response (i.e., “hunting” vs. “transit”) to physical aspects of their environment (e.g., ice concentration). Weddell seal foraging was concentrated to within 5 km of a breathing hole, and they appear to move between holes as local food is depleted. There were regional differences in behavior so that seals at Davis traveled greater distances (three times more) and spent less time in hunting mode (half the time) than seals at DDU. Despite these differences, hunting dives at both locations were pelagic, concentrated in areas of high ice concentration, and over areas of complex bathymetry. There was also a seasonal change in diving behavior from transiting early in the season to more hunting during winter. Our observations suggest that Weddell seal foraging behavior is plastic and that they respond behaviorally to changes in their environment to maximize food acquisition and storage. Such plasticity is a hallmark of animals that live in very dynamic environments such as the high Antarctic where resources are unpredictable.     

Annual and diurnal variations in the underwater vocalizations of Weddell seals

Summary Weddell seal vocalizations were recorded once a fortnight throughout 1984 at a major pupping site near Davis, Antarctica. Few vocalizations were heard between January and June. The number of vocalizations recorded increased from July to a peak in November and early December during the breeding period and then fell off rapidly through December. The increase in the number of seal vocalizations was correlated with a build up in seal numbers but some of the increase may be explained by an increased rate of vocalization by males.     

Weddell seal in-air call sequences made with closed mouths

Weddell seals (Leptonychotes weddelli) near Davis, Antarctica, produce a number of in-air vocalizations during the breeding season. With mouth and nostrils closed, pups and adults of both sexes produce at least 8 call types. Many of these are similar in nature to the sounds made underwater. Calls range from long, high frequency (>5 kHz) whistles to short, low frequency (<0.2 kHz) grunts. Individual call elements are often repeated and up to 6 call types are strung together in highly variable sequences.     

Population structure of ice-breeding seals

The development of population genetic structure in ice-breeding seal species is likely to be shaped by a combination of breeding habitat and life-history characteristics. Species that return to breed on predictable fast-ice locations are more likely to exhibit natal fidelity than pack-ice-breeding species, which in turn facilitates the development of genetic differentiation between subpopulations. Other aspects of life history such as geographically distinct vocalizations, female gregariousness, and the potential for polygynous breeding may also facilitate population structure. Based on these factors, we predicted that fast-ice-breeding seal species (the Weddell and ringed seal) would show elevated genetic differentiation compared to pack-ice-breeding species (the leopard, Ross, crabeater and bearded seals). We tested this prediction using microsatellite analysis to examine population structure of these six ice-breeding species. Our results did not support this prediction. While none of the Antarctic pack-ice species showed statistically significant population structure, the bearded seal of the Arctic pack ice showed strong differentiation between subpopulations. Again in contrast, the fast-ice-breeding Weddell seal of the Antarctic showed clear evidence for genetic differentiation while the ringed seal, breeding in similar habitat in the Arctic, did not. These results suggest that the development of population structure in ice-breeding phocid seals is a more complex outcome of the interplay of phylogenetic and ecological factors than can be predicted on the basis of breeding substrate and life-history characteristics.     

WEDDELL SEAL UNDERWATER CALLING RATES DURING THE WINTER AND SPRING NEAR MAWSON STATION, ANTARCTICA

Underwater vocalization monitoring and surveys, both on ice and underwater, were used to determine if Weddell seals ( Leptonychotes weddellii ) near Mawson Station, Antarctica, remain under the fast ice during winter within close range of breeding sites. Daytime and nighttime underwater calling rates were examined at seven breeding sites during austral winter and spring to identify seasonal and diel patterns. Seals rarely hauled out at any of the sites during winter, although all cohorts (adult males, females, and juveniles) were observed underwater and surfacing at breathing holes throughout winter (June–September) and spring (October–December). Seal vocalizations were recorded during each sampling session throughout the study ( n = 102 daytime at seven sites collectively, and n = 5 24-h samples at each of two sites). Mean daytime calling rate was low in mid-winter (July) (mean = 18.9 ± 7.1 calls/min) but increased monthly, reaching a peak during the breeding season (November) (mean = 62.6 ± 15.7 calls/min). Mean nighttime calling rate was high throughout the winter and early spring (July–October) with mean nocturnal calling rate in July (mean = 61.8 ± 35.1 calls/min) nearly equal to mean daytime calling rate in November (during 24-h daylight). Reduced vocal behavior during winter daylight periods may result from animals utilizing the limited daylight hours for nonvocal activities, possibly feeding.     

Feast or famine: evidence for mixed capital–income breeding strategies in Weddell seals

Evolved patterns of resource expenditure for reproduction have resulted in a life history continuum across species. A strictly capital-breeding strategy relies extensively on stored energy for reproduction, whereas income breeding uses energy acquired throughout the reproductive period. However, facultative income breeding has been shown in some classically capital-breeding animals, and was originally thought to provide a nutritional refuge for smaller females incapable of securing sufficient reserves during pre-partum foraging. We examined milk composition and milk output for the Weddell seal to determine to what degree lactation was aided by food intake, and what factors contributed to its manifestation. Milk composition was independent of maternal post-partum mass and condition, but did change over lactation. Changes were most likely in response to energetic and nutritional demands of the pup at different stages of development. During early lactation, females fasted and devoted 54.9% of total energy loss to milk production. Later in lactation 30.5% more energy was devoted to milk production and evidence suggested that larger females fed more during lactation than smaller females. It appears that Weddell seals may exhibit a flexible strategy to adjust reproductive investment to local resource levels by taking advantage of periods when prey are occasionally abundant, although it is restricted to larger females possessing the physiological capacity to dive for longer and exploit different resources during lactation. This supports the assumption that although body mass and phylogenetic history explain most of the variation in lactation patterns (20–69%), the remaining variation has likely resulted from physiological adaptations to local environmental conditions. Our study confirms that Weddell seals use a mixed capital–income breeding strategy, and that considerable intraspecific variation exists. Questions remain as to the amount of energy gain derived from the income strategy, and the consequences for pup condition and survival. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The dynamics of male harem dominance in southern elephant seals (Mirounga leonina) at the South Shetland Islands

Breeding chronology, harem structure and changes in male harem dominance were studied at Stranger Point, Isla 25 de Mayo/King George Island, principally by extensive field census work during the 2003 breeding season. Males were individually identified and their size estimated by using a photogrammetric method. Peak female haul out for the population occurred on 31 October, when a total of 276 females were observed along 7 km of coastline, distributed in ten harems with a median size of 16 females. Overall sex ratio and harem sex ratio for the breeding population were 1:6.7 and 1:10.6, respectively. A total of 33 males were identified associated with harems. Male size conferred an advantage in terms of dominance hierarchy, since dominant males (4.91±0.15 m) were significantly longer than subordinate males (4.63±0.19 m). Harems were dominated by an average of 4.5 (range 2–7) different males during the breeding season. Elephant seals at Stranger Point breed in very low density aggregations. The main breeding events in this population occurred later than at other breeding sites, which agrees with previous observations in the area. Male movement among harems suggests that differences in mating success among males could be achieved through their different behaviours.     

The post-moult diet of Emperor Penguins (Aptenodytes forsteri) in the eastern Weddell Sea,Antarctica

The diet of emperor penguins Aptenodytes forsteri was studied during late austral summer at Drescher Inlet, eastern Weddell Sea, Antarctica. Antarctic krill Euphausia superba was a major component of the food, accounting for 75% of all prey items. Emperor penguins appear to feed on krill during shallow dives under the fast sea ice. Fish, mainly nototheniids, accounted for less than 20% by number of all prey. An evaluation of the main prey types in terms of mass indicated, however, that fish represented up to 75% approximately of prey mass. Feeding experiments were performed on captive penguins and showed that squid beaks can accumulate for up to 3 weeks within the stomach without any clear signs of erosion. The lack of cephalopod soft parts in the samples makes it likely that all squid beaks were derived from animals captured some time previously. Squid seems to be a very minor dietary component of emperor penguins at the Drescher Inlet.     

Geographic variation of Weddell seal (<Emphasis Type="Italic">Leptonychotes weddellii</Emphasis>) airborne mother–pup vocalisations

Geographic variation of vocal behaviour may be reflective of genetic, cultural and ecological differences between locations. Such differences have been previously reported in six pinnipeds, including Weddell seals (Leptonychotes weddellii). This study investigated whether the acoustic characteristics of airborne Weddell seal mother and pup ‘contact’ calls vary geographically between the Vestfold Hills and McMurdo Sound. From each location, 72 mother and 120 pup calls were analysed, with 11 acoustic characteristics measured. MANOVA and Discriminant function analysis (DFA) identified significant differences in several fundamental frequency characteristics. The cross-validated DFA classified greater than 60% of mother and pup vocalisations to the correct location. For novel calls, the probabilities of correctly classifying these percentages by chance are low. Additionally, ordinal logistic regression identified significant differences in the maximum energy distribution of mother and pup vocalisations. For pups, this variation is likely the result of genetic differences between the two populations. Nevertheless, results support suggestions that, when compared with underwater repertoire differences, airborne within-call differences are less efficient at identifying Weddell seal breeding populations.     

Influence of age and individual identity in the use of breeding colony habitat by male Weddell seals in Erebus Bay,Antarctica

Male–male contest behavior can contribute to spatial distributions of male pinnipeds during breeding seasons. To maximize breeding opportunities, the most competitive males would be expected to be surrounded by the highest numbers of reproductive-age females. As information regarding fine-scale spatial ecology of Weddell seals is lacking, we performed an exploratory study using kernel density analyses to evaluate age-specific habitat use of male Weddell seals in Erebus Bay, Antarctica. Additionally, we investigated the relationship between age and number of surrounding reproductive-age females using a competing set of regression models in a Bayesian framework that considered different functional forms of age while incorporating individual heterogeneity. As male adult Weddell seals aged, to at least 20 years, they were more likely to be found in areas associated with the greatest densities of reproductive-age females, but individual heterogeneity also influenced the number of reproductive-age female neighbors. The youngest males tended to haul out in offshore areas associated with better hunting, and older males tended to settle in more nearshore areas associated with more pup production. Our findings from this preliminary investigation indicate that male Weddell seal spatial behavior during the breeding season varies with age and individual and might be related to reproductive activity.     

Sex‐related differences in the postmolt distribution of Weddell seals (Leptonychotes weddellii) in the southern Weddell Sea

The population of Weddell seals (Leptonychotes weddellii) in the southern Weddell Sea is in a unique position on the continental shelf edge, with vast shelf waters to the south, and deep Southern Ocean to the north. We describe sex‐related differences in the winter distribution of this population, from data collected by 20 conductivity‐temperature‐depth satellite relay data loggers deployed in February 2011 at the end of the annual molt. The regional daily speed was calculated, and a state‐space model was used to estimate behavioral states to positions along individuals’ tracks. GLMMs estimated that males and smaller individuals, diving in shallower water, traveled less far per day of deployment (males 14.6 ± 2.26 km/d, females 18.9 ± 2.42 km/d), and males were estimated to dive in shallower water (males 604 ± 382 m, females 1,875 ± 1,458 m). Males and smaller individuals were also estimated to be more resident; males spent an average 83.4% ± 7.7% of their time in a resident behavioral state, compared to females at 74.1% ± 7.1%. This evidence that male and female Weddell seals in the southern Weddell Sea are adopting different strategies has not been shown elsewhere along their circumpolar distribution.     

An apparent population decrease,or change in distribution,of Weddell seals along the Victoria Land coast

Ground counts during 1959–1968 compared with counts using high resolution (0.6 m²) satellite imagery during 2008–2012 indicated many fewer Weddell seals (Leptonychotes weddellii) at two major molting areas in the western Ross Sea: Edisto Inlet‐Moubray Bay, northern Victoria Land, and McMurdo Sound, southern Victoria Land. Breeding seals have largely disappeared from Edisto‐Moubray, though the breeding population in McMurdo Sound appears to have recovered from harvest in the 1960s. The timing of decline, or perhaps spreading (lower numbers of seals in more places), is unknown but appears unrelated to changes in sea ice conditions. We analyzed both historic and satellite‐derived ice data confirming a large expansion of pack ice mostly offshore of the Ross Sea, and not over the continental shelf (main Weddell seal habitat), and a thinning of fast ice along Victoria Land (conceivably beneficial to seals). Timing of fast ice presence and extent in coves and bays along Victoria Land, remains the same. The reduction in numbers is consistent with an altered food web, the reasons for which are complex. In the context of a recent industrial fishery targeting a seal prey species, a large‐scale seal monitoring program is required to increase understanding of seal population changes.     

Underwater calling rates of harp and Weddell seals as a function of hydrophone location

Stereo recordings of harp seal (Pagophilus groenlandicus) and Weddell seal (Leptonychotes weddellii) underwater vocalizations were made near breeding groups using separations between two hydrophones of 159–339 m. Within a large herd, harp seal call numbers varied slightly between channels. Counts of Weddell seal calls were higher near a small herd on the ice than 159–180 m away. Repeat counts of harp seal calls by a single observer differed significantly. Source levels of Weddell seal calls varied and higher amplitude calls would be detected up to 2 orders of magnitude farther away than quieter calls. Hydrophone location (especially near small groups), observer variability and call source level differences will bias the use of monitoring underwater seal vocalizations to index locations, population size or underwater behaviours. Using hydrophone arrays and multiple observers may mitigate these problems. Accepted: 15 September 2000     

Flight propensity and diapause incidence in five populations of the bark beetle Ips typographus in Scandinavia

Emergence from brood logs, take-off activity and the duration of tethered flight was recorded in the first laboratory generation of the bark beetle Ips typographus L. (Coleoptera: Scolytidae) from five locations (ca 300 km apart) in Sweden and Denmark. Beetles of northerly origin emerged later from brood logs. This pattern was associated with an increasing proportion on non-fliers towards the north. After overwintering, both the rate of development of flight activity and the proportion of non-fliers were the same among populations. Flight duration of fliers was similar among populations and appeared unaffected by outbreak conditions.     

Movements of adult female Weddell seals during the winter months

The focus of this study was the distribution of adult female Weddell seals during winter at the Vestfold Hills. Satellite tracking of Weddell seals had never been done before at this location. Hence, this was a pilot study to evaluate the following methods. We attached satellite transmitters to the lower back, where there was least potential to change the seals’ behaviour or to damage instruments on the ice. Location data were obtained only where the seals hauled out, not necessarily where they were feeding. All locations were within the area of fast-ice that was associated with the Vestfold Hills. There were gaps of up to 30 days in the location data sets. Each instrument (n=3) remained attached and functioning for ca. 6 months. During that time, two of the three seals hauled out within small areas adjacent to, or nearby, open water. The same seals hauled out sporadically. We inferred that these seals foraged offshore whilst returning to fast-ice to rest. If Weddell seals forage beneath dynamic ice but return to stable ice as their preferred resting substrate, then evidence of haulout sites will always be a biased measure of foraging range. Tracking seals in the water may be possible using alternative placement of transmitters. However, there is potential for instruments to interfere with movement (breathing and prey capture). For this reason, we recommend a combination of sensors, diet and tracking haulout sites to research winter foraging.     

Three-dimensional dive profiles of free-ranging Weddell seals

We used an acoustic tracking system to record under-ice movements of two free-ranging adult male Weddell seals. The two males were unconstrained and interacting with other Weddell seals at a breeding colony in McMurdo Sound, Antarctica. We reconstructed three-dimensional paths of 279 dives by these seals. All dives were less than 20-min duration and none were deeper than 220 m. These three-dimensional dive profiles were compared with conventional time-depth dive profiles recorded using microprocessor loggers. We assigned each of the 279 dives to 1 of 6 classes using an existing classification scheme on the basis of the time-depth trace. Within these, two-dimensionally derived, classes the actual three-dimensional dive profiles at times varied profoundly. Additional parameters obtained with the acoustic system, such as bearing and distance travelled between diving and surfacing points, demonstrate that significant, additional, biologically important information can be derived from the three-dimensional data. Accepted: 19 December 1999     

Long-term monitoring of Antarctic pinnipeds in Admiralty Bay (South Shetlands, Antarctica)

Year-round monitoring of five Antarctic pinnipeds was conducted in Admiralty Bay from 1988 up to 2000. Two breeding species: southern elephant sealsMirounga leonina (Linnaeus, 1758) and Weddell sealsLeptonychotes weddellii (Lesson, 1826), were present throughout the year. Three other species: crabeater seals Lobodon carcinophagus (Hobron and Jacquinot, 1842), leopard sealsHydrurga leptonyx (Blainville, 1820), and Antarctic fur sealsArctocephalus gazella (Peters, 1875) visited the area only for short periods. During this study, the abundance of elephant seals was stable, whereas those of Weddell and crabeater seals declined. Leopard seals numbers fluctuated irregularly. We detected a possible immigration from South Georgia: of a stable magnitude for elephant seals, and of variable magnitude, depending on food accessibility, for Antarctic fur seals. We found a strong recurrence of the spatial distributions of elephant, Weddell, and Antarctic fur seals in the 13 oases on the shore of Admiralty Bay. Annual distribution patterns were characteristic for each species. The innermost beaches were used predominantly by the animals during their annual fasts: the breeding and the moulting seasons.     

Absence of clinal variation in virgin retention capacity in Australian Drosophila melanogaster

The ability of virgin Drosophila melanogaster adults to retain eggs is thought to be an adaptation to persisting in temperate areas, based on differences in this trait between European and African populations, and based on seasonal changes in this trait in France. By retaining eggs in the absence of males and under conditions of poorer nutrition (conditions common in temperate areas during colder months), females reduce the wastage of resources and increase their probability of surviving spring into summer, enabling them to initiate summer population expansions. To test for variation in virgin egg retention along a climatic gradient, we characterized clinal variation in strains collected from eastern Australia extending from temperate Tasmania to tropical northern Queensland. Despite testing a large number of strains and repeated testing of the cline ends, we did not detect any evidence for clinal variation in virgin egg retention. Therefore although D. melanogaster in temperate Australia overwinter at the adult stage, there is no evidence for selection on virgin retention capacity producing clinal patterns. This contrasts with other evidence for clinal variation in egg production patterns over winter.