The magnetic intensities were measured by a gaussmeter.    From Wordnik.com.  [PLoS Biology: New Articles] Reference

Bats and bees use the earth’s magnetic fields for navigation and EMF interferes with this, but crows simply do not like EMF and will caw loudly at a high EMF if this happens to you, test yourself with a gaussmeter. do you have body metal that may conduct more emf?.    From Wordnik.com.  [What’s up with the crows? « knitnut.net] Reference