Compare and Contrast

I had intended to do my butterfly survey today but the forecast had changed for the worse so I deferred it till tomorrow. Instead, I had a couple of hours on my patch. It seemed unpromising until as I was on the return leg, I heard my first Willow Warbler of the year. Seconds later I spotted my first Yellowhammer of the year. It's so hard to tell Willow Warblers from Chiffchaffs, but luckily at this time of year it's obvious fro their songs which are completely different.