First, let me point out that the calculation I am about to do is completely bogus (i.e. it will have absolutely nothing to do with the reality of eagles). The population growth formula only works in a set of ideal conditions, namely there has to be unlimited food and space for the eagles and there has to be no changes in conditions during the time period involved.
Of course with eagles in the US over the a period of 40 years this isn't the case at all. There has been human activity with loss of habitat. There have been changes in laws to provide protection. There are ups and downs in disease rates and prey availability.
This means that the population growth formula is completely unsuited for describing anything having to do with reality when it comes to actual eagles in the US.
If you were growing eagles in a petri dish (assuming you provided ample food and space) this formula would be correct. Other than that circumstance, this calculation is bogus... but let's do it anyway.
Starting with the formula Px = Po(1+y)^n Let's solve for y...
Px/Po = (1+y)^n
(Px/Po)^(1/n) = 1 + y
y = (Px/Po)^(1/n) -1
If I haven't made a stupid mistake in my quick calculations, I get about 8.04% per year.
But did I make it clear enough that this calculation is bogus?