Timing of squid migration reflects North Atlantic climate variability. (9/1226)

The environmental and biotic conditions affecting fisheries for cephalopods are only partially understood. A problem central to this is how climate change may influence population movements by altering the availability of thermal resources. In this study we investigate the links between climate and sea-temperature changes and squid arrival time off southwestern England over a 20-year period. We show that veined squid (Loligo forbesi) migrate eastward in the English Channel earlier when water in the preceding months is warmer, and that higher temperatures and early arrival correspond with warm (positive) phases of the North Atlantic oscillation (NAO). The timing of squid peak abundance advanced by 120-150 days in the warmest years ('early' years) compared with the coldest ('late' years). Furthermore, sea-bottom temperature was closely linked to the extent of squid movement. Temperature increases over the five months prior to and during the month of peak squid abundance did not differ between early and late years, indicating squid responded to temperature changes independently of time of year. We conclude that the temporal variation in peak abundance of squid seen off Plymouth represents temperature-dependent movement, which is in turn mediated by climatic changes associated with the NAO. Such climate-mediated movement may be a widespread characteristic of cephalopod populations worldwide, and may have implications for future fisheries management because global warming may alter both the timing and location of peak population abundance.  (+info)

Great bustard population structure in central Spain: concordant results from genetic analysis and dispersal study. (10/1226)

We found significant sex differences in the mtDNA genetic structure and dispersal patterns of great bustards in a population of 11 breeding groups, "leks", in central Spain. The analysis of genetic distances showed that the female population was divided into three groups of leks separated by ca. 50 km, whereas male haplotypes were randomly distributed among leks. Genetic distances among pairs of leks were positively correlated with geographical distances in females but not in males. While female haplotype distributions were homogeneous among leks at close distances, differences in male genetic structure were highly variable even between two close leks. These results from genetic analyses were concordant with those from a radiotracking study on natal dispersal. Natal dispersal distances were higher in males than in females. Also, the frequency of movement of a female between two leks was positively correlated with their genetic affinity and geographical proximity. In males, the frequency of movement was correlated with geographical proximity but not with genetic affinity. Males dispersed among genetically unrelated leks, contributing to keep nuclear genetic diversity in the population, whereas females tended to be philopatric. These results suggest that isolation-by-distance influences the distribution of maternal lineages at a regional level.  (+info)

Migrating songbirds tested in computer-controlled Emlen funnels use stellar cues for a time-independent compass. (11/1226)

This paper investigates how young pied flycatchers, Ficedula hypoleuca, and blackcaps, Sylvia atricapilla, interpret and use celestial cues. In order to record these data, we developed a computer-controlled version of the Emlen funnel, which enabled us to make detailed temporal analyses. First, we showed that the birds use a star compass. Then, we tested the birds under a stationary planetarium sky, which simulated the star pattern of the local sky at 02:35 h for 11 consecutive hours of the night, and compared the birds' directional choices as a function of time with the predictions from five alternative stellar orientation hypotheses. The results supported the hypothesis suggesting that birds use a time-independent star compass based on learned geometrical star configurations to pinpoint the rotational point of the starry sky (north). In contrast, neither hypotheses suggesting that birds use the stars for establishing their global position and then perform true star navigation nor those suggesting the use of a time-compensated star compass were supported.  (+info)

Swimming speeds and buoyancy compensation of migrating adult chum salmon Oncorhynchus keta revealed by speed/depth/acceleration data logger. (12/1226)

Although the homing migration of Pacific salmon is well documented, the swimming behaviour of the returning salmon has been poorly described, principally as a result of the difficulties encountered in monitoring salmon behaviour in the sea. The present study describes the use of a recently developed electronic data logger to obtain simultaneous recordings of the swimming speed, depth, fin-beating activity and body angle of free-ranging chum salmon Oncorhynchus keta during their homing migration in coastal waters. Chum salmon migrated horizontally at speeds of 1.5-3.0 km h(-1). The gross horizontal distance salmon moved during total recording periods were 1.24- to 19.0-fold greater than the net distance from the release site to the retrieval points. It is suggested that homing salmon did not drift passively but swam actively to the spawning grounds. Salmon preferred the surface water, but also made frequent vertical migrations. The travelled depth of each salmon ranged from 0.36 to 0.64 km per hour. Salmon descended at faster rates and steeper angles than they ascended. Both tailbeat frequency and tail thrust were higher during the ascent than the descent phase. These results suggest that chum salmon spent more energy during the ascent than the descent phase. Profiles of descent rate assumed an arched shape with respect to a change in hydrostatic pressure, while ascent rate increased with decreasing depth. High tailbeat frequencies were found during the course of ascent, which suggests that the salmon did not regulate the volume of air in the swim bladder during short-term vertical migrations.  (+info)

The diving behaviour of green turtles undertaking oceanic migration to and from Ascension Island: dive durations, dive profiles and depth distribution. (13/1226)

Satellite telemetry was used to record the submergence duration of green turtles (Chelonia mydas) as they migrated from Ascension Island to Brazil (N=12 individuals) while time/depth recorders (TDRs) were used to examine the depth distribution and dive profiles of individuals returning to Ascension Island to nest after experimental displacement (N=5 individuals). Satellite telemetry revealed that most submergences were short (<5 min) but that some submergences were longer (>20 min), particularly at night. TDRs revealed that much of the time was spent conducting short (2-4 min), shallow (approximately 0.9-1.5 m) dives, consistent with predictions for optimisation of near-surface travelling, while long (typically 20-30 min), deep (typically 10-20 m) dives had a distinctive profile found in other marine reptiles. These results suggest that green turtles crossing the Atlantic do not behave invariantly, but instead alternate between periods of travelling just beneath the surface and diving deeper. These deep dives may have evolved to reduce silhouetting against the surface, which would make turtles more susceptible to visual predators such as large sharks.  (+info)

Neurons of the central complex of the locust Schistocerca gregaria are sensitive to polarized light. (14/1226)

The central complex is a topographically ordered neuropil structure in the center of the insect brain. It consists of three major subdivisions, the upper and lower divisions of the central body and the protocerebral bridge. To further characterize the role of this brain structure, we have recorded the responses of identified neurons of the central complex of the desert locust Schistocerca gregaria to visual stimuli. We report that particular types of central complex interneurons are sensitive to polarized light. Neurons showed tonic responses to linearly polarized light with spike discharge frequencies depending on e-vector orientation. For all neurons tested, e-vector response curves showed polarization opponency. Receptive fields of the recorded neurons were in the dorsal field of view with some neurons receiving input from both compound eyes and others, only from the ipsilateral eye. In addition to responses to polarized light, certain neurons showed tonic spike discharges to unpolarized light. Most polarization-sensitive neurons were associated with the lower division of the central body, but one type of neuron with arborizations in the upper division of the central body was also polarization-sensitive. Visual pathways signaling polarized light information to the central complex include projections via the anterior optic tubercle. Considering the receptive fields of the neurons and the biological significance of polarized light in insects, the central complex might serve a function in sky compass-mediated spatial navigation of the animals.  (+info)

Linking breeding and wintering ranges of a migratory songbird using stable isotopes. (15/1226)

We used the natural abundance of stable isotopes (carbon and hydrogen) in the feathers of a neotropical migrant songbird to determine where birds from particular breeding areas spend the winter and the extent to which breeding populations mix in winter quarters. We show that most birds wintering on western Caribbean islands come from the northern portion of the species' North American breeding range, whereas those on more easterly islands are primarily from southern breeding areas. Although segregated by breeding latitude, birds within local wintering areas derive from a wide range of breeding longitudes, indicating considerable population mixing with respect to breeding longitude. These results are useful for assessing the effects of wintering habitat loss on breeding population abundances and for predicting whether the demographic consequences will be concentrated or diffuse.  (+info)

Protein loss during long-distance migratory flight in passerine birds: adaptation and constraint. (16/1226)

During long-distance flights, birds catabolize not only fat but also protein. Because there is no storage form of protein, protein catabolism entails a structural or functional loss. In this study, we investigated which organs were most reduced in lean mass during different phases of fat store loss and whether protein loss can be regarded as adaptive or as a constraint. Body and organ composition were analysed both during the autumn migration over continental Europe (sample from Switzerland) and after a long-distance flight over the Sahara and the Mediterranean Sea in spring (sample from Ventotene, Italy) in four species of passerine bird: pied flycatcher Ficedula hypoleuca, willow warbler Phylloscopus trochilus, garden warbler Sylvia borin and barn swallow Hirundo rustica. Large variations in protein mass occurred when long non-stop flights were performed. After a long-distance flight, birds showed a marked increase in net protein loss when fat stores were nearing depletion (analogous to the late phase of endurance fasting when the rate of protein catabolism is increased). When fat reserves were above approximately 5-10 %, protein was derived from all organs, but particularly from the breast muscles. When fat stores diminished further and protein catabolism increased, the mass of the digestive organs was reduced fastest. When the decrease in breast muscle mass during flight was regarded in terms of potential flight performance, it appeared that the use of breast muscle protein with decreasing body mass can be regarded as adaptive as long as fat stores did not reach a critical level. Below approximately 5-10 % body fat, however, protein loss reduced flight performance. This demonstrates that the phase of fasting (the size of the remaining fat stores) is an important condition for understanding the occurrence and effects of protein loss during endurance flights.  (+info)