I'm nowhere near being an ornithologist Tam but this offering may be a piece of the puzzle.
Some years ago, while I lived in Mafikeng, South Africa, there were red kites in huge numbers but only in summer. I was told that they are migratory and were moving back and forth between Africa as far down as I was and Russia as far north as Siberia, where they go for summer. I also know that macro weather events can influence migratory patterns and we have had some unusual weather lately.
Now lets see what the experts say!