Has anyone noticed that lots of the birdhouses going up the last few years have that extra slot subtly located in the back? Combination bird/bat houses!
OK, another tangent...
Last night on tv I saw that bird songs recorded now don't match the ones from decades ago. They are fairly consistently louder and higher pitched. The theory is that they've evolved to better carry over the greatly increased background noise caused by humans, as we've invaded so much of their habitat.