Rodney is a physicist studying bird flight, John is... also somehow involved with birds. Park ranger? Ornithologist? Guy who scales cliff faces to put tags on peregrine falcons? Guy who brings owls into classrooms? Regardless, he clearly thinks birds are cool because they can fly. Their paths cross, there are digs about Rodney's sunscreen and John's bird's-nest hair, John knows all the good spots (interpret that as you will), etc.
Thanks to ileliberte for the most wonderful betaing.