Effects of blood parasite infections on spatiotemporal migration patterns and activity budgets in a long-distance migratory passerine

How blood parasite infections influence the migration of hosts remains a lively debated issue as past studies found negative, positive or no response to infections. This particularly applies to small birds, for which monitoring of detailed migration behaviour ovea whole annual cycle has been technically unachievable so far. Here, we investigate how bird migration is influenced by parasite infections. To this end, we tracked great reed warblers (Acrocephalus arundinaceus) with multi-sensor loggers, characterized general migration patterns as well as detailed flight bout durations, resting times and flight heights and related these to the genus and intensity of their avian haemosporidian infections. We found migration distances to be shorter and the onset of autumn migration to be delayed with increasing intensity of blood parasite infection, in particular for birds with Plasmodium and mixed-genus infections. Additionally, the durations of migratory flight bout were prolonged for infected compared to uninfected birds. But since severely infected birds and particularly birds with mixed genus infections had shorter resting times, initial delays seemed to be compensated for and the timing in other periods of the annual cycle was not compromised by infection. Overall, our multi-sensor logger approach revealed that avian blood parasites have mostly subtle effects on migratory performance and that effects can occur in specific periods of the year only

Migratory Reed Warblers Need Intact Trigeminal Nerves to Correct for a 1,000 km Eastward Displacement

Several studies have shown that experienced night-migratory songbirds can determine their position, but it has remained a mystery which cues and sensory mechanisms they use, in particular, those used to determine longitude (east-west position). One potential solution would be to use a magnetic map or signpost mechanism like the one documented in sea turtles. Night-migratory songbirds have a magnetic compass in their eyes and a second magnetic sense with unknown biological function involving the ophthalmic branch of the trigeminal nerve (V1). Could V1 be involved in determining east-west position? We displaced 57 Eurasian reed warblers (Acrocephalus scirpaceus) with or without sectioned V1. Sham operated birds corrected their orientation towards the breeding area after displacement like the untreated controls did. In contrast, V1-sectioned birds did not correct for the displacement. They oriented in the same direction after the displacement as they had done at the capture site. Thus, an intact ophthalmic branch of the trigeminal nerve is necessary for detecting the 1,000 km eastward displacement in this night-migratory songbird. Our results suggest that V1 carries map-related information used in a large-scale map or signpost sense that the reed warblers needed to determine their approximate geographical position and/or an east-west coordinate

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

Dataset for the main results of "Navigation by extrapolation of geomagnetic cues in a migratory songbird"

Preprocessed data for mean individual directions of orientation of Eurasian reed warblers (Acrocephalus scirpaceus). The dataset was used for the main result figure (Figure 3. Predictions and results for the virtual magnetic displacements) in the publication titled "Navigation by extrapolation of geomagnetic cues in a migratory songbird". This dataset shows the orientation of birds in two experiments: (1) Experiment 1 when the birds were tested under the natural magnetic field conditions (NMF), and then under the declination-only changed magnetic field condition (dCMF); (2) Experiment 2 when the orientation of birds was first tested under the NMF conditions and when all magnetic field parameters were changed (aCMF). We tested the orientation of long-distance migrants, Eurasian reed warblers, exposing them to geomagnetic cues of unfamiliar magnitude only encountered beyond their natural distribution range. The birds demonstrated re-orientation towards their natural migratory corridor as if they were translocated to the corresponding geographic location but only when all naturally occurring magnetic cues were presented, not when declination was changed alone. This result represents direct evidence for migratory birds’ ability to navigate using geomagnetic cues extrapolated beyond the range of magnitude they previously experienced

An attempt to develop an operant conditioning paradigm to test for magnetic discrimination behavior in a migratory songbird

Birds are thought to possess two magnetosensory systems: (1) a chemical sensor in the bird’s eye, and (2) a magnetoreceptor innervated by the ophthalmic branch of the trigeminal nerve (V1) and presumably located in the upper beak. It has been recently demonstrated that the visually mediated magnetosensory system is crucial to the magnetic compass of the European Robin (Erithacus rubecula). In contrast, the trigeminal nerve system, despite neuronal responses to magnetic stimuli, is neither necessary nor sufficient for magnetic compass orientation in this species. Unfortunately, the potential role of the trigeminal organ is unlikely to be elucidated by the classical behavioral paradigm of the orientation cage, because it tests only for spontaneous compass responses. An operant conditioning study by Mora et al. (Nature 432:508–511, 2004) demonstrated that Homing Pigeons can be conditioned to discriminate the presence and absence of a strong gradient magnetic field stimulus. This discrimination depended on intact ophthalmic branches of the trigeminal nerves. Here, we report detailed attempts aimed at adapting the behavioral paradigm used by the above study for a model migratory bird, the European Robin. We tested three variants of a conditioning procedure very similar to that of Mora et al. (Nature 432:508–511, 2004). Despite extensive training, we were not able to demonstrate that our experimental birds were able to discriminate the magnetic stimuli presented to them. This was, however, not due to a general unsuitability of the conditioning setup for this species, because the robins were able to successfully discriminate the presence and absence of an auditory stimulus in the same setup