while it is understood that the major audience for this site will be composed by people that are at least familiar with the imperial system of measurements (e.g. people from the Commonwealth and the U.S.), this site will attract people from all over the Internet, most of which have no clue as to what an inch, a pound or a foot corresponds to - the vast majority of the world uses SI measurements.

The Falco peregrinus entry, for example, requires most people to convert from inches to cm in order to have an idea of the size of the bird.

While google calculator can and will help, it would be fitting for a site that aims to disseminate knowledge to present measurements in metric units alongside those in imperial units in order to make the site usable for everyone.

If space is a constraint, then only SI measurements should be used, as they are 1. used by the majority of the world countries and 2. used in science in general.

Point taken.