Comparison of light- and SST-based geolocation with satellite telemetry in free-ranging albatrosses

Light-based archival tags are increasingly being used on free-ranging marine vertebrates to study their movements using geolocation estimates. These methods use algorithms that incorporate threshold light techniques to determine longitude and latitude. More recently, researchers have begun using sea surface temperature (SST) to determine latitude in temperate regions. The accuracy and application of these algorithms have not been validated on free-ranging birds. Errors in both geolocation methods were quantified by double-tagging Laysan (Phoebastria immutabilis Rothschild) and black-footed (P. nigripes Audubon) albatrosses with both leg-mounted archival tags that measured SST and ambient light, and satellite transmitters. Laysan albatrosses were captured and released from breeding colonies on Tern Island, northwestern Hawaiian Islands (23°52N, 166°17W) and Guadalupe Island, Mexico (28°31N, 118°10W) and black-footed albatrosses from Tern Island. Studies were carried out between December 2002 and March 2003. For all birds combined, the mean ± SD great circle (GC) distance between light-based locations and satellite-derived locations was 400±298 km (n=131). Errors in geolocation positions were reduced to 202±171 km (n=154) when light-based longitude and SST-based latitude (i.e. SST/light) were used to establish locations. The SST/light method produced comparable results for two Laysan albatross populations that traveled within distinctly different oceanic regions (open ocean vs more coastal) whereas light-based methods produced greater errors in the coastal population. Archival tags deployed on black-footed albatrosses returned a significantly higher proportion of lower-quality locations, which was attributed to interference of the light sensor on the tag. Overall, the results demonstrate that combining measures of light-based longitude and SST-based latitude significantly reduces the error in location estimates for albatrosses and can provide valid latitude estimates during the equinoxes, when light-based latitude measurements are indeterminate.Communicated by J.P. Grassle, New Brunswick     

Pacific harbor seals (<Emphasis Type="Italic">Phoca vitulina</Emphasis>) and salmon: genetics presents hard numbers for elucidating predator-prey dynamics

We used a PCR-based species test and microsatellite genotyping to determine salmonid species composition and quantity of Chinook among Pacific harbor seal (Phoca vitulina) prey. Tests were applied to DNA extracted from all salmonid bones recovered from scat (fecal) samples. Condition of bone samples and quantity of DNA varied substantially. Although DNA extraction and species identification was only successful for just over half of the bone samples, 93% of all scat samples had bones that were identified to species. Most often only a single salmonid prey species was evident within a scat sample (39% exclusively coho and 46% exclusively Chinook) but 13% contained bones from more than one species of salmonid. For scat samples that contained Chinook bones, 68% had skeletal remains from the same fish and 32% had bones from more than one individual Chinook, varying in number from two to four individuals per scat. In one case, bones from one individual Chinook were recovered in three different scat samples.     

Quantitative analysis of aggregation behavior in juvenile blacktip sharks

Aggregation patterns of a population of juvenile blacktip sharks (Carcharhinus limbatus) within a summer nursery area were examined over a period of 3 years using an array of acoustic monitors. Individually coded acoustic tags were surgically implanted into 33–40 neonate sharks each year from 2000 to 2002 and their presence monitored continuously by the acoustic array. Data from the acoustic monitors was processed to estimate the center of activity location of each tagged shark every 30 min. Nearest neighbor analysis of shark locations revealed that sharks aggregated within the nursery in all years of the study. Sharks were aggregated most commonly during the early and late summer months (June, October and November) and became less common through the middle of the study period each year (July–September). Temporal periodicity within the data revealed a strong diel pattern with sharks aggregating during the day and dispersing at night, except in June when aggregations often persisted through the night. Aggregations were generally restricted to the mid and northern sections of the study site. Reasons for aggregations may include predator avoidance or improved feeding efficiency.     

Carbon monoxide levels at a toll plaza near Durban, South Africa

Reliable measurements of pollutant levels in the vicinity of a toll plaza appear to be rare. In order to assess the exposure of toll booth operators to carbon monoxide, a continuous carbon monoxide monitor was installed at head height in the booth of a medium density traffic lane at the Mariannhill toll plaza, situated on a busy highway near Durban, South Africa. Measurements in excess of 500 ppmv were recorded and the high daily mean carbon monoxide concentrations may account for some of the symptoms such as headaches and general malaise that have been reported by workers in the booths. Generally, carbon monoxide levels recorded far exceed the recommended limit set by the South African authorities. These results have led to recommendations regarding the structure of new and existing toll booths to minimize the exposure of toll booth workers to adverse effects of vehicle-emitted pollutants.     

The Cost Efficiency of Wild Dog Conservation in South Africa

Abstract:  Aside from Kruger National Park, no other suitable reserves of sufficient size exist in South Africa that will hold a viable population of wild dogs ( Lycaon pictus ). Consequently, conservation efforts have been focused on creating a metapopulation through a series of wild dog reintroductions into isolated fenced reserves. Additional potential exists for conserving wild dogs on private ranch land. Establishing the metapopulation was an expensive process, accounting for approximately 75% of the US$380,000 spent on wild dog conservation in South Africa during 1997-2001. The principal goal of the metapopulation project was to reduce the risk of catastrophic population decline. Now that this has been achieved, we developed a uniform cost-efficiency index to estimate the cost efficiency of current and potential future conservation strategies in South Africa. Conserving wild dogs in large protected areas was predicted to be the most cost-efficient conservation strategy (449 packs/$100,000 expenditure). Establishing the metapopulation has been less cost efficient (23 packs/$100,000), and expansion of the metapopulation was predicted to be even less cost efficient if predation by wild dogs results in additional costs, as is to be expected if private reserves are used for reintroductions (3-13 packs/$100,000). Because of low logistical costs, conserving wild dogs in situ on private ranch land was potentially more cost efficient than reintroducing wild dogs (14-27 packs/$100,000). We recommend that donor funding be used to reintroduce wild dogs into transfrontier parks, when they are established, to maintain the existing metapopulation and to establish conservation programs involving wild dogs on private ranch land. Investing in the expansion of the metapopulation should be limited to state-owned nature reserves willing to carry predation costs without compensation.     

Density affects female and male mate searching in the fiddler crab, <Emphasis Type="Italic">Uca beebei</Emphasis>

In most species, only one sex searches for mates while the other waits. Models of sex-specific mate-searching behavior predict single-sex searching, but the factors that determine which sex searches are not understood. In this study, we examine the effects of density and predation risk on mate-searching behavior in the fiddler crab Uca beebei. U. beebei is one of the few fiddler-crab species in which both sexes search for mates. In a field experiment conducted in Panama, we manipulated crab density and perceived predation risk in replicate plots. Females searched more and males searched less at high densities. At high levels of perceived predation risk, both sexes similarly reduced their search rates. Observations of plots that naturally varied in crab density show that females were more likely to search for mates in areas of higher density, where there were more males. Females may preferentially search for mates in high-density areas because the abundance of nearby burrows, into which they can run to escape predators, decreases their costs of searching and because the abundance of males and male burrows facilitates comparisons and thus may increase their benefits from searching. Males at high densities decrease their mate-searching rate perhaps in response to the increase in female searching and to the corresponding increase in the intensity of their competitors' mate-attraction signals.     

Chemosensory cues allow courting male garter snakes to assess body length and body condition of potential mates

When choosing between two potential mates, a male may benefit by picking a larger (longer and/or more heavy-bodied) female because she is likely to produce more or larger offspring. Males of many species use visual cues to evaluate the sizes of their mates, but in some situations (at night or in a crowded mating swarm), vision may be useless. Potentially, males may be able to use chemical cues that convey information about female body size. We manipulated cues available to free-ranging male garter snakes (Thamnophis sirtalis parietalis) in large courting aggregations near communal dens in Manitoba, Canada. Males not only directed disproportionate courtship to longer and heavier-bodied females, but also courted most vigorously in response to lipids extracted from the skins of such females. Our data show that with a flick of his tongue, a male garter snake can identify not only a female's body length, but also her body condition.     

Spatial and temporal variations in sediment accumulation in an algal turf and their impact on associated fauna

Marine Biology - The relationships between the fauna inhabiting an intertidal algal turf, Osmundea pinnatifida, and the accumulated sediment were studied in the autumn and summer. The investigation...     

Reproductive conflict in animal societies: hierarchy length increases with colony size in queenless ponerine ants

Dominance interactions determine reproductive status in many animal societies, including many cooperatively breeding vertebrates and eusocial Hymenoptera without queen-worker dimorphism. Typically, the dominant individual monopolises reproduction, and subordinates behave like helpers. In Dinoponera queenless ants, workers are totipotent females and can potentially reproduce, yet only the top-ranking worker actually reproduces. Individual workers ranked immediately below the dominant breeder worker (gamergate) are hopeful reproductives. Whether or not a worker benefits from joining the hierarchy of high-ranking workers depends on the trade-off between the probability of becoming dominant and reproducing directly, and the colony-level cost of an additional lazy high ranker. Inclusive fitness models predict that the length of the dominance hierarchy depends on relatedness, colony size, and the linearity of the hierarchy. Here, we test the effect of colony size by comparing hierarchy length among three species that differ in colony size (Dinoponera australis: median=14 workers, quartiles=10 and 19 workers; D. gigantea: median=41, quartiles=33 and 74; D. quadriceps: median=78, quartiles=55 and 90). Although difficulties in defining where the hierarchy ends hamper comparisons, the results are in broad agreement with the predictions. Hierarchies are close to the predicted lengths and are longer in species with larger colonies (one, three and three workers in the three species in order from smallest to largest colony vs two, three and four predicted). These conclusions are further supported by determining Kokko and Lindström's λ index of skew, which is smaller (i.e. characteristic of a longer hierarchy) in species with larger colonies.     

Feeding preferences,seasonal gut repletion indices,and diel feeding patterns of the sea urchin<Emphasis Type="Italic"> Tripneustes gratilla</Emphasis> (Echinodermata: Echinoidea) on a coastal habitat off Toliara (Madagascar)

The feeding biology of the echinoid Tripneustes gratilla from a seagrass bed off Toliara, on the south-west coast of Madagascar, was investigated during the summer and winter seasons. Repletion indices of the gut of T. gratilla varied seasonally, in such a way that higher amounts of food occurred in the gut in winter than in other seasons. Conversely, a more detailed analysis of one summer and one winter sample of the gut tissue dry weights revealed higher weights in summer (February) than in winter (August). This was interpreted as a varying capability of nutrient storage and closely related to the feeding activity of the echinoid. This inverse relationship between feeding activity and nutrient storage was suggested to be dependent on gonadal growth. Indeed, higher food consumption was observed during the post-spawning period (August), that is, when most of the energy accumulated was used up for gonadal growth. Low feeding activity occurred when a sufficient amount of energy was accumulated in gut tissues (February), the time corresponding to the initiation of gonadal growth. Investigations on the feeding habits, using Ivlev's electivity index, revealed preferential feeding of T. gratilla on Syringodium isoetifolium, the dominant seagrass species found in the gut. This was partly related to the higher availability of that particular seagrass species in the field. However, its soft and terete leaf blade's morphology also makes it easier to manipulate and ingest. Studies on the feeding behaviour indicated the presence of a diel feeding cycle in T. gratilla individuals in both summer and winter seasons. Yet, its pattern varied between the two studied months (one summer and one winter) as the cycle was less contrasted during period of active feeding, i.e. in winter compared to summer. This study provides novel information on how intrinsic factors, such as physiological state, can govern the feeding activity of T. gratilla living in a seagrass habitat.