Greg Armfield, Nairobi National Park, 19 November 2015

It was amazing to see the comments roll in, from friends and strangers, saying, 'I can't believe you missed that, Greg'

Even people in my own office asked, "Did you really miss that?" On my Facebook page, I posted a few photos I took of the rhinos before this shot was taken, but the reality is that after you've taken 1,000 pictures of black rhinos mating - because they go at it for quite a long time - it gets a bit boring.

I'm a senior producer for the World Wide Fund for Nature, and I was in Kenya when this was taken, back in November. A film crew was documenting our work and I was there to help produce and do the photography. We decided to travel from the Maasai Mara to Nairobi national park to document a day in the life of Harrison Njoroge Kamande, the Kenya Wildlife Service rhino patrol leader, and his team. We wanted to capture their movements and see how they document the rhinos' activity.