The folks at Nature Canada are seeking entries for their 2015 Photo Contest. They have been very upfront about their contest and I think that their rules and regulations are very clear.
Information about the contest is located here. As I always do, I encourage members to read the rules very carefully to know exactly what irrevocable rights you give away. Because Nature Canada is being straight up, you'll see that they could use your images to promote their contest on social media that we know takes a very loose methodology when it comes to the work of private artists, notably Facebook and Instagram. If you choose to enter, my recommendation will be to email your entry to Nature Canada directly as your preferred method. I understand that these folks are happy to see your entry on Facebook or Twitter if appropriately tagged, just understand that you basically throw your rights away when you post on those services directly.
Full rules are located here.
Please also note that content alterations to images are not permitted, but B&W conversions, tonal corrections and by that extension, basic post processing are ok. I read this to mean no composites, no removal of content or addition of content that wasn't really there.
Entries received prior to June 30th and July 31st respectively become eligible for early bird prizes. Formal contest entry closure is August 14th with public voting starting September 1st.