This shot is an unusual one for me but I ended up really like it. Its an odd one though for a couple reasons.
The first is that Cliff Swallows are just strange little creatures, in general. Rather than nesting, they make these mud structures on the underside of cliffs by slowly flying little pieces of mud up and sticking it upside down to the roof of cliffs and caves. The process is incredibly tedious but creates a nest that is very strong and safe.
The second is that it was taken with my 300mm lens with a teleconverter on it. I've been going through this experiment where I go out with the 300mm with the tele on it rather than my 500mm or 600mm for the specific reason of boosting the maximum magnification. This shot would have been extremely difficult to make with the longer teles as they have 4m minimum focus distance and only a maximum magnification around 0.16 but my 300mm + TC gets up to a 0.34 maximum magnification allowing me to take a shot of a tiny subject like this filling the frame. In most situations, there isn't much benefit to doing this but in this case it really worked out. I am also just in love with how the Nikon 300mm PF renders detail. I don't know what it is, but I have several shots in my portfolio I've made with it that just seem to have this really clean but super sharp look that I haven't been able tor replicate with other lenses.