Altered Orientation and Flight Paths of Pigeons Reared on Gravity Anomalies: A GPS Tracking Study

Abstract

The mechanisms of pigeon homing are still not understood, in particular how they determine their position at unfamiliar locations. The “gravity vector” theory holds that pigeons memorize the gravity vector at their home loft and deduct home direction and distance from the angular difference between memorized and actual gravity vector. However, the gravity vector is tilted by different densities in the earth crust leading to gravity anomalies. We predicted that pigeons reared on different gravity anomalies would show different initial orientation and also show changes in their flight path when crossing a gravity anomaly. We reared one group of pigeons in a strong gravity anomaly with a north-to-south gravity gradient, and the other group of pigeons in a normal area but on a spot with a strong local anomaly with a west-to-east gravity gradient. After training over shorter distances, pigeons were released from a gravitationally and geomagnetically normal site 50 km north in the same direction for both home lofts. As expected by the theory, the two groups of pigeons showed divergent initial orientation. In addition, some of the GPS-tracked pigeons also showed changes in their flight paths when crossing gravity anomalies. We conclude that even small local gravity anomalies at the birth place of pigeons may have the potential to bias the map sense of pigeons, while reactivity to gravity gradients during flight was variable and appeared to depend on individual navigational strategies and frequency of position updates.

Route Fidelity during Marine Megafauna Migration

“…However, the possibility that animal orientation is informed by gravitational cues remains largely untested. The empirical results we present suggest further experiments, like those performed by Blaser et al (2013Blaser et al ( , 2014, Fisahn et al (2015), and Cresci et al (2017) will improve our understanding of the role, if any, gravity plays in animal orientation. We particularly encourage experimental tests on model organisms (e.g., zebrafish, Danio rerio; honey bees, Apis mellifera; eels, Anguilla spp.)…”

“…We focus our analyses on magnetic inclination and vertical gravitational acceleration cues (see Nomenclature for a glossary of terms) as experimental studies have suggested both can serve as exogenous sources of orientation information during animal movement (Wiltschko and Wiltschko, 1972;Larkin and Keeton, 1978;Keeton, 1979;Kanevskyi et al, 1985;Light et al, 1993;Lohmann and Lohmann, 1994;DeVries et al, 2004;Putman et al, 2011;Blaser et al, 2013Blaser et al, , 2014. By focussing our analyses on route fidelity movements, our research is directly relevant to positional orientation during migration, one of the greatest unknowns in animal navigation science (Gould, 2004).…”

Gravity anomalies without geomagnetic disturbances interfere with pigeon homing – a GPS tracking study

“…The Ukraine was chosen because its central part contains massive and well-mapped gravity anomalies distributed in a predominantly flat countryside without any long-distance visual cues. In a first study (Blaser et al, 2013b), we could verify two predictions of the gravity vector theory: (i) pigeons raised in neighboring lofts yet on anomalies with different inclinations of the gravity vector showed different vanishing bearings, with wrongly departing birds maintaining that direction over long distances, and (ii) pigeons appeared to sense gravity anomalies as indicated by changes of their flight course. However, the gravity anomalies in that study were partially associated with geomagnetic anomalies.…”

“…The observed range at the anomaly and control release site is very small. Geomagnetic variations in the Ukraine can peak at 10,000 nT (see also Blaser et al, 2013b). Red diamonds indicate release sites; red lines are beelines between the release site and loft; red arrows indicate the home direction.…”

Sensory mechanisms of long-distance navigation in birds: a recent advance in the context of previous studies

“…However, gravity was proposed by some authors as a natural coordinate(s) used by birds for navigation (Blaser et al 2013(Blaser et al , 2014Dornfeldt 1991;Kanevskyi 1985;Larkin and Keeton 1978;Lednor and Walcott 1984). A few attempts have been made to experimentally test the effect of gravitational changes (lunar cycles) or gravitational anomalies on homing performance in pigeons.…”