Who is considered the best source for Wild Bird info?

Cornell Lab of Ornithology & National Audubon Society both list Northern Cardinal weight at 42 - 48 grams.

Identification Guide to North American Birds/Pyle list it at 37 - 54 grams

That is a big difference, none of them have a citation to a reference source (I guess that is because they are considered a source). Do they just pull numbers out of the air?