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All offshore oil and gas platforms have finite economic life spans. One of the decommissioning options for these platforms is complete removal, requiring the use of explosives to dislodge the [...]

Several marine animals, including salmon and sea turtles, disperse across vast expanses of ocean before returning as adults to their natal areas to reproduce. How animals accomplish such feats of natal homing has remained an enduring mystery. Salmon are known to use chemical cues to identify their home rivers at the end of spawning migrations. Such cues, however, do not extend far enough into the ocean to guide migratory movements that begin in open-sea locations hundreds or thousands of kilometers away. Similarly, how sea turtles reach their nesting areas from distant sites is unknown. However, both salmon and sea turtles detect the magnetic field of the Earth and use it as a directional cue. In addition, sea turtles derive positional information from two magnetic elements (inclination angle and intensity) that vary predictably across the globe and endow different geographic areas with unique magnetic signatures. Here we propose that salmon and sea turtles imprint on the magnetic field of their natal areas and later use this information to direct natal homing. This novel hypothesis provides the first plausible explanation for how marine animals can navigate to natal areas from distant oceanic locations. The hypothesis appears to be compatible with present and recent rates of field change (secular variation); one implication, however, is that unusually rapid changes in the Earth's field, as occasionally occur during geomagnetic polarity reversals, may affect ecological processes by disrupting natal homing, resulting in widespread colonization events and changes in population structure. migration | navigation | magnetic | magnetoreception | fish

Research concerning the importance of philopatry to stopover sites in the Bet Shean Valley in Israel for Reed Warblers preparing to cross the Sahara Desert is presented. Adult birds arrive earlier than youngsters.

A bird-borne data logger, which stores flight directions at regular intervals, was used to reveal the foraging patterns of Thick-billed Murres (Uria lomvia) breeding at Latrabjarg in northwestern Iceland. Tracked birds traveled 10 to 168 km one-way to foraging sites in a narrow sector to the northwest of the breeding colony. The pattern of foraging activity was rather constant. Outbound birds stopped briefly several times, possibly testing prey availability. The longest stops occurred at sites close by the turning point of the outbound journey. During the inbound flight, stops were less frequent and shorter than on the outbound flight, suggesting that the sequence of stops was not the expression of a disturbance caused by the instruments.

Recent studies of mitochondrial DNA (mtDNA) variation among marine turtle populations are consistent with the hypothesis that females return to beaches in their natal region to nest as adults. In contrast, less is known about breeding migrations of male marine turtles and whether they too are philopatric to natal regions. Studies of geographic structuring of restriction fragment and microsatellite polymorphisms at anonymous nuclear loci in green turtle (Chelonia mydas) populations indicate that nuclear gene flow is higher than estimates from mtDNA analyses. Regional populations from the northern and southern Great Barrier Reef were distinct for mtDNA but indistinguishable at nuclear loci, whereas the Gulf of Carpentaria (northern Australia) population was distinct for both types of marker. To assess whether this result was due to reduced philopatry of males across the Great Barrier Reef, we determined the mtDNA haplotypes of breeding males at courtship areas for comparison with breeding females from the same three locations. We used a PCR-restriction fragment length polymorphism approach to determine control region haplotypes and designed mismatch primers for the identification of specific haplotypes. The mtDNA haplotype frequencies were not significantly different between males and females at any of the three areas and estimates of [F.sub.st] among the regions were similar for males and females ([F.sub.st] = 0.78 and 0.73, respectively). We conclude that breeding males, like females, are philopatric to courtship areas within their natal region. Nuclear gene flow between populations is most likely occurring through matings during migrations of both males and females through nonnatal courtship areas.

Translocation is increasingly being advocated as a nonlethal management alternative for species, particularly mammals. The efficiency of translocation was evaluated based on the trapability, site fidelity, post release survival and homing ability of California ground squirrels. The survival rate until 18 days after translocation was 71-79%, with mortality highest soon after release. 85% established new home ranges, but homing success was lower with translocation distance. Translocation is probably not suitable for squirrel control over large areas, but has potential for use in smaller areas.

During a field experiment on density-dependent processes in meadow voles (Microtus pennsylvanicus), we removed 848 voles from field enclosures and released them 1,200 m away. Eleven animals (1.3%) returned to the enclosure from which they had been removed, which entailed traversing inhospitable habitat (forest, wetland), obstacles (permanent stream, roads), and climbing a 0.9-m hardware-cloth fence surrounding the enclosures. For six of the 11 voles, returning home was accomplished in > 2 but < 4 weeks; the others returned in [less than or equal to]2 weeks. Voles returning home, which averaged ca. 30 g, lost on average 5.3% of their body mass during homing, unlike their resident counterparts, which gained mass. The voles that homed could not have used familiar objects as cues for navigation, but whether they used distant points of reference or wandered randomly is unknown. Our findings suggest that meadow voles are capable of travelling > 1 km toward home, and thus, it is likely that they could travel similar distances while dispersing. Key words: Microtus pennsylvanicus, meadow vole, dispersal, long-distance homing, movement distances

A study has been conducted to examine the effect of relocation on the survival of the grizzly bear, Ursus arctos, transported in the Yellowstone National Park. Survival was determined according to the ability of the bears to return to the capture site. Transported bears had lower survival rates than those not transported. Bears that were transported at distances greater than 75 km. decreased their return rates. These results suggest that the homing ability of bears is influenced by distance. Results also suggest that return rates and survival rates are determined by the bears' age-sex group.

A study was conducted to examine animal locations and movements of black-tailed deer using Schoener's Ratio at four sites on Vancouver Island, British Columbia, from 1982-1984. Location data were obtained by measuring bearings at three separate stations with 100-m. intervals. Datasets which lack independence were attributed to migrations and animal movements within the home range. These observations skewed data distributions and eliminated normality in the independence test. Thus, it is suggested to examine animal locations symmetrically based on time rather than on time intervals.

Aerial surveys to locate radio-marked Canada geese (Branta canadensis interior) of the Mississippi Valley Population (MVP) indicated fall and spring migration 1984-86 was concentrated in a corridor in central Illinois and southeastern Wisconsin. A major spring staging area was identified in the Kaskaskia River Valley of central Illinois. Chronology of departure from wintering areas varied annually, but timing of departure from Wisconsin staging areas and arrival on nesting areas in Ontario was similar among years. Chronology of fall migration varied annually, and timing of movements of birds from Wisconsin to southern Illinois caused underestimates in midwinter population inventories (conducted mid-Dec) in 3 of 4 years. Homing rates of segments of the MVP associated with fall staging in Winconsin versus southern Illinois did not differ (P > 0.20) from rates that could be expected based on numbers of geese using Wisconsin versus Illinois in fall. We found no evidence to support the existence of manageable subpopulations of the MVP.

An isolated, unpaired, male red-cockaded woodpecker, in danger of losing its habitat because of a planned timber harvest, was moved 16.7 km to a reserve in Vernon Parish, LA. Subsequent observations show that the bird returned to the captive site, despite being relocated twice more. After the third translocation, he was again captured at the captive site. The study suggests that the distance between the capture and release sites should be more than 20 km if the birds are not to return to the original site.

Several studies and tools are employed to explain the spatial ecology and to determine the diurnal annual and seasonal home-range size for male and female lynx in northern Maine. The spatial ecology and densities of the southern and northern lynx populations are shown to be quite similar in the presence of large number of hares.

Habitat loss and fragmentation affect forest birds through direct loss of breeding habitats, detrimental edge effects such as increased nest predation and brood parasitism, and possibly by limiting movements among remaining forest patches. Despite indirect evidence suggesting that landscape-scale bird movements are constrained by open areas, skepticism remains because birds routinely cross inhospitable terrain during migration. Here, we report evidence from 201 independent homing trials showing that landscape composition and configuration influence the movements (1-4 km) of two neotropical migrant (Black-throated Blue Warbler, Dendroica caerulescens and the Ovenbird, Seiurus aurocapillus) and one resident (Black-capped Chickadee, Poecile atricapillus) forest bird species in Quebec, Canada. Trials consisted of translocating territorial, mated males and measuring the time they needed to return to their territories (homing time), as well as the probability with which they returned to their territories within 30 h (homing success). Birds took more time and were less likely to return to their territories as forest cover decreased in the landscape. Once the simple linear variation due to forest cover was removed from landscape configuration variables, their influence on homing time and success was nonexistent or subtle, suggesting that landscape composition has greater predictive value than landscape configuration to infer constraints on forest bird movements. Indeed, and contrary to our expectation, mean nearest-neighbor distance between forest patches had no impact on homing time or success, but its coefficient of variation was positively correlated with homing time and negatively correlated with homing success. On the other hand, homing time and success were not influenced by the number of forest patches or the amount of edge per unit of forest cover. These results were consistent for all three bird species that we studied. Our data support the hypothesis that movements are constrained when forest birds travel in deforested and fragmented landscapes outside migratory periods. Such an impediment is likely to disrupt habitat selection processes, reduce the colonization of isolated forest patches, and ultimately, alter population structure and dynamics. Key words: agricultural landscape; Black-capped Chickadee; Black-throated Blue Warbler; connectivity; corridor; dispersal; forest cover; fragmentation; habitat loss; movement; Ovenbird.

Pinyon Jays (Gymnorhinus cyanocephalus) live in permanent flocks of 50-500 individuals on apparently undefended home ranges. We present date collected from 1973 to 1982 on the movement of individuals into and out of a color-banded flock. We banded 681 wanderers from other flocks, 46 of whom immigrated and bred in the study flock. Three hundred and eighty-three juveniles and yearlings born in the study flock disappeared from the natal flock; 22 of these bred in a neighboring flock. One was collected in 1973 as a yearling 600 km from its place of birth. Most dispersal occurred in the fall, but yearling females also dispersed during the breeding seasons. Fall dispersal was primarily by juveniles and included males and females in equal abundance. Females transferred between neighboring flocks more often than males. Many males returned to their natal flocks after months of wandering. As a result, 89% of male yearlings, but only 48% of female yearlings, in the study flock were born there. Annual variability in dispersal by yearlings was correlated with sex ratio in their natal and neighboring flocks; females joined flocks with strongly male-biased sex ratios and females left flocks with female-biased sex ratios. Low status of juveniles and yearlings, especially females, may explain why some dispersal occurred each year regardless of the sex ratio of the flock. Homing ability and the number of relatives in a flock were only weakly related to the percentage of yearlings and juveniles emigrating. Five consequences of dispersal were: (1) flock members may become familiar with resources outside their home range; (2) the sex ratio of yearlings approaches 1:1, despite extreme and variable sex ratio biases among yearlings born in the flock; (3) in some years the yearling cohort is predominantly composed of immigrants and in other years natives predominate; (4) immigrants have fewer relatives in the flock than natives have; and (5) the effective population size ranges from 222 to 370 and includes breeders of a flock and breeders in neighboring flocks.

Recent research on the homing mechanisms of pigeons may soon shed light on the issue and initiate further studies on pigeon behavior. More data are pouring in which indicate the presence of a magnetic based receptor in some species. More experiments are also being conducted on the mechanism of light-dependent magnetic sensors. The rational behind the 'village effect' or the tendency to fly towards villages is still under debate.

Philopatry in migratory species can apply to any location used during the annual cycle. The degree of philopatry influences the genetic structure of populations, but only at the stage of the annual cycle when pair formation and gene exchange occur. Because pair formation in birds typically occurs during the breeding season, most studies have focused on breeding-site philopatry. Waterfowl (Anseriformes) are an important exception to this pattern because pair formation often occurs during the winter months. Yet, surprisingly few studies have examined winter philopatry in waterfowl. To serve as an impetus for future research, we summarize published information on winter philopatry in waterfowl and examine these patterns in light of current hypotheses proposed to explain philopatric behavior. Our analyses indicate that geese, swans, and sea ducks show high levels of winter philopatry, with homing rates varying between 49 and 98% to small study areas. In contrast, return rates (0 to 20%) and homing rates (35 to 85%) to large study areas probably are comparatively lower for dabbling ducks and pochards. Unfortunately, detailed comparisons among groups are hindered by variation in the scale at which philopatric behavior is evaluated (ranging from