Originally posted by W412ren Either that or just extremely lucky.
Being able to predict in advance which two days of the year these birds would be nest building would be next to impossible. When my step son lived in Niagara falls I would go on photo excursions down to the falls 2 or three times week, just because they were there. Images like that are completely a result fo the amount of time I spend walking around with a camera with full kit, at least 4 lenses,. A lot of days it's for nothing. Other days you get images no one else is prepared for. The DA*200 2.8 is great for that. It's very light weight for a telephoto and can be just thrown in the bag, even if I don't expect to use it.
I came back the next day with the Tamron 300 2.8 (which is just to heavy to carry all over the place without some reason for thinking you might need it.) , but the moment was gone. You need to be prepared for the moment.