Experienced migratory songbirds do not display goal-ward orientation after release following a cross-continental displacement: an automated telemetry study

The ability to navigate implies that animals have the capability to compensate for geographical displacement and return to their initial goal or target. Although some species are capable of adjusting their direction after displacement, the environmental cues used to achieve this remain elusive. Two possible cues are geomagnetic parameters (magnetic map hypothesis) or atmospheric odour-forming gradients (olfactory map hypothesis). In this study, we examined both of these hypotheses by surgically deactivating either the magnetic or olfactory sensory systems in experienced white-throated sparrows (Zonotrichia albicollis) captured in southern Ontario, Canada, during spring migration. Treated, sham-treated, and intact birds were then displaced 2,200 km west to Saskatchewan, Canada. Tracking their initial post-displacement migration using an array of automated VHF receiving towers, we found no evidence in any of the groups for compensatory directional response towards their expected breeding grounds. Our results suggest that white-throated sparrows may fall back to a simple constant-vector orientation strategy instead of performing true navigation after they have been geographically displaced to an unfamiliar area during spring migration. Such a basic strategy may be more common than currently thought in experienced migratory birds and its occurrence could be determined by habitat preferences or range size

A Visual Pathway Links Brain Structures Active during Magnetic Compass Orientation in Migratory Birds

The magnetic compass of migratory birds has been suggested to be light-dependent. Retinal cryptochrome-expressing neurons and a forebrain region, “Cluster N”, show high neuronal activity when night-migratory songbirds perform magnetic compass orientation. By combining neuronal tracing with behavioral experiments leading to sensory-driven gene expression of the neuronal activity marker ZENK during magnetic compass orientation, we demonstrate a functional neuronal connection between the retinal neurons and Cluster N via the visual thalamus. Thus, the two areas of the central nervous system being most active during magnetic compass orientation are part of an ascending visual processing stream, the thalamofugal pathway. Furthermore, Cluster N seems to be a specialized part of the visual wulst. These findings strongly support the hypothesis that migratory birds use their visual system to perceive the reference compass direction of the geomagnetic field and that migratory birds “see” the reference compass direction provided by the geomagnetic field

Behavioral adaptations and constraints on avian diving - a northern hemisphere perspective

Tropical forests support some of the world’s richest centres of species diversity and endemism, yet these biomes are now dangerously imperilled by anthropogenic change, including deforestation and habitat degradation, overexploitation, global climate change, and the invasion of alien predators and competitors. If we are to avert or at least mitigate catastrophic loss of species in these areas, it is vital to understand the direct and indirect effects of these agents of threat. Moreover, provision of a robust theoretical and empirical underpinning for the relationship between evolved characteristics (life-history traits and ecological preferences) and extinction risk may provide a general theory of the extinction process useful for conservation management. Forest birds provide some of the best quantitative data on the rate and selectivity of the extinctions in tropical regions, and their autecology is better known than most other taxonomic groups, making them ideal candidates for the tropical application and testing of extinction theory and viability models. I show how direct population, habitat and threat data, in combination various lines of surrogate information, can be used to develop a broad predictive framework for extinction vulnerability of tropical birds using generalized linear mixed modelling and multi-model inference from an a priori set of population dynamics simulations. Case studies, including the Sulewesi maleo, are provided. The results emphasise an important disconnection between the proximate processes that dominate the fate of small bird populations on the edge of extinction and the ultimate and often broad-scale anthropogenic drivers that are causing once abundant tropical species to decline

Eurasian reed warblers compensate for virtual magnetic displacement

SummaryDisplacement studies have shown that long-distance, night-migrating songbirds are able to perform true navigation from their first spring migration onwards [1,2]. True navigation requires both a map and a compass. Whereas birds are known to have sun, star, and magnetic compasses, the nature of the map cues used has remained highly controversial. There is quite strong experimental evidence for the involvement of olfactory map cues in pigeon and seabird homing [3]. In contrast, the evidence for the use of magnetic map cues has remained weak and very little is known about the map cues used by long-distance migratory songbirds. In earlier experiments [2,4], we have shown that Eurasian reed warblers physically displaced 1,000 km eastward from Rybachy to Zvenigorod (Figure 1) re-orient towards their breeding destinations by changing their orientation in Emlen funnels from the NE to the NW. We have also previously shown that this re-orientation cannot be explained by a ‘jetlag effect’ [5]. We have now used this model system to show that Eurasian reed warblers use geomagnetic map cues to determine their position

Differences of the geomagnetic field parameters between capture site, displacement site and a putative goal area.

<p>(<i>A</i>) Difference in total intensity; (<i>B</i>) Difference in inclination; (<i>C</i>) Difference in declination. The measured geomagnetic field parameters at Rybachy (the left dot) were the following: total intensity 50,688 nT, inclination 70.3°, declination 5.6°. The measured geomagnetic field parameters at Zvenigorod (the right dot) were the following: total intensity 52,175 nT, inclination 71.2°, declination 10.1°. As a goal site (the upper dot), the centroid of “the goal” shown on <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065847#pone-0065847-g001" target="_blank">Figure 1</a> (60° 30′N, 27° 51′E) was taken. Computation of the Earth’s magnetic field parameters for the goal site was done with the calculator of IGRF Model 11 in the website of the National Geophysical Data Center (<a href="http://www.ngdc.noaa.gov/geomag/geomag.shtml" target="_blank">http://www.ngdc.noaa.gov/geomag/geomag.shtml</a>). The calculated geomagnetic field parameters at the goal site were the following: total intensity 52,172 nT, inclination 73.7°, declination 8.9°. The charts with the isolines of the geomagnetic field parameters are taken from <a href="http://pubs.usgs.gov/sim/2007/2964" target="_blank">http://pubs.usgs.gov/sim/2007/2964</a> with modifications.</p

Orientation of birds at the capture and displacement site.

<p>(<i>A, C</i>) Results for sham-sectioned birds, before sham-surgery at the capture site (<i>A</i>) and after sham-surgery and translocation to the displacement site (<i>C</i>). (<i>E, G</i>) Results for V1-sectioned birds before V1-sectioning at the capture site (<i>E</i>) and after V1-sectioning surgery and translocation to the displacement site (<i>G</i>). For description of the circular diagrams and the map (<i>D</i>), see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065847#pone-0065847-g001" target="_blank">Figure 1</a>. The schemes of real V1-section (<i>F</i>) and sham section (<i>B</i>) show the approximate locations of the three branches of the trigeminal nerve. The ophthalmic branch (V1) is shown in bold. The crosses on <i>F</i> indicate the approximate locations at which the nerve was sectioned and a piece of the nerve was removed. For details about the surgeries, see Methods.</p