Different responses in two strains of chickens (Gallus gallus) in a magnetic orientation test.

Previous studies demonstrated that layer strain domestic chicks bred for egg production can orient using directional cues from the magnetic field; here we report that chicks from a broiler strain bred for meat production do not use magnetic cues for orientation. We imprinted both strains of chicken on a red ball and subsequently trained them in a featureless testing arena. Between rewarded trials in the geomagnetic field, we inserted unrewarded tests under the following conditions: (1) in the geomagnetic field, (2) in a magnetic field with North shifted by 90 degrees and (3) in a magnetic field with the inclination inverted. The layer chicks made a correct axial response in 75-80% of the tests, shifting their choices following a rotation of magnetic North. Chicks of the broiler strain, in contrast, performed at chance level with between 47 and 60% of choices on the correct axis. This difference between the strains does not appear to be due to substantial strain differences in motivation to perform the task. It therefore appears possible that the selection of the broiler strain has led to the elimination of the specific ability to respond to magnetic cues in the test situation.