Geo-coded?

I found 4 more eggs on my Swamp Milkweed today. I am having incredible luck finding eggs! And so early! My friend, Sara, asked me in an e-mail if perhaps Monarchs were geo-coded to somehow come back to the same gardens each year. Interesting concept. I wonder how we could prove that? Afterall, they are coded somehow, through four generations, to return to the very same Mariposa Monarcha Bioshere Reserves in Mexico each fall. Hmm...