The magnetic map hypothesis proposes that animals can use spatial gradients in the Earth's magnetic field to help determine geographic location. This ability would permit true navigation--reaching a goal from an entirely unfamiliar site with no goal-emanating cues to assist. It is a highly contentious hypothesis since the geomagnetic field fluctuates in time and spatial gradients may be disturbed by geological anomalies. Nevertheless, a substantial body of evidence offers support for the hypothesis. Much of the evidence has been indirect in nature, such as the identification of avian magnetoreceptor mechanisms with functional properties that are consistent with those of a putative map detector or the patterns of orientation of animals exposed to temporal and/or spatial geomagnetic anomalies. However; the most important advances have been made in conducting direct tests of the magnetic map hypothesis by exposing experienced migrants to specific geomagnetic values representing simulated displacements. Appropriate shifts in the direction of orientation, which compensate for the simulated displacements, have been observed in newts, birds, sea turtles, and lobsters, and provide the strongest evidence to date for magnetic map navigation. Careful experimental design and interpretation of orientation data will be essential in the future to determine which components of the magnetic field are used to derive geographic position.

No abstract

Spatial variation in the inclination of the geomagnetic field has been implicated in the map component of homing by eastern red-spotted newts Notophthalmus viridescens. Here we show that when newts are exposed to small changes in magnetic inclination, the most dramatic effects on homing orientation occur at values close to the 'home value', as predicted by the magnetic map hypothesis (Phillips 1996). Newts reverse the direction of homing orientation over a range of inclination of 0.5 degrees spanning the home value, providing further evidence that magnetic inclination or one of its components (i.e., vertical or horizontal intensity) is used to derive map information.

No abstract

A study was conducted at a semi-arid site near Mt Mary, South Australia. Fifty-eight adult sleepy lizards, Tiliqua rugosa, were radio-tagged and regularly located over the spring season, when they are most active, for 2-5 years. Home-range area did not differ between males and females. Changes in home-range position between years were assessed by the distance between home-range centres measured at intervals of one, two, three or four years. Mean distances for successive years were less than the span of the home range in one year. The distance did not differ between sexes, it was not related to lizard size, nor did it increase with increased time interval. This implies that for the resident adult population, lizards retain their home ranges for at least five years, and that the sexes do not differ in their fidelity to home range.

No abstract

Previous studies have demonstrated the presence of a light-dependent magnetic compass in a urodele amphibian, the eastern red-spotted newt Notophthalmus viridescens, mediated by extraocular photoreceptors located in or near the pineal organ. Newts tested under long-wavelength ( ‡500 nm) light exhibited a 90°shift in the direction of orientation relative to newts tested under full spectrum (white) or short-wavelength light. Here we report that bullfrog tadpoles Rana catesbeiana (an anuran amphibian) exhibit a 90°shift in the direction of magnetic compass orientation under long-wavelength ( ‡500 nm) light similar to that observed in newts, suggesting that a common light-dependent mechanism mediates these responses. These findings suggest that a lightdependent magnetic compass may have been the ancestral state in this group of vertebrates.Correspondence: Michael J. Freake,

Comparisons of recent and historic population demographic studies of eastern hellbenders Cryptobranchus alleganiensis alleganiensis have identified significant population declines and extirpations associated with habitat degradation, poor water quality and disease, leading to nomination as a candidate for listing under the Endangered Species Act. However, populations in the southern Appalachian region of the range have received less attention despite relatively high levels of watershed protection due to the establishment of federally protected National Forest and National Park public lands. These watersheds likely represent some of the best remaining available habitat, yet the lack of published studies make assessment of population stability and viability very difficult. Our objectives were to (1) conduct a capture-mark-recapture (CMR) demographic study and a point transect survey on the Hiwassee River in Tennessee which is designated a National Scenic River, and is largely contained within the Cherokee National Forest, (2) quantify the size structure of the population, (3) compare abundance, survival and recruitment with historic and contemporary hellbender populations across the range, (4) assess the importance of this population and the significance of National Forest and National Park lands in the context of hellbender population conservation in the southeastern United States. We detected all age classes present, with larval hellbenders comprising 21.5% of captures. Using a combination of static life table and CMR methods, we determined that survival rates during the first year were low (~10%), but were high (68–94%) for taggable sized hellbenders. Density of hellbenders at the study site was very high (84 taggable sized hellbenders per 100m of river) compared to recent demographic studies conducted in other regions of the range. We detected hellbenders over ~28 km of river, with a mean density of 23 taggable sized hellbenders per 100m of river, and a total population estimate of 6440 taggable hellbenders. National Forest and National Park lands are likely to continue to play a particularly important role in providing suitable habitat for hellbenders in the southern Appalachians. In fact, only six of 21 known hellbender locations in Tennessee appear to show consistent larval recruitment, all of which are located within or adjacent to National Forest or National Park land.