Hi can someone tell me why this happens every year. A perfect nest but no chicks. I've been putting the box up in the position shown for five years. The first year there were chicks but none since. I dont think the problem is cats. I see very few. It may be squirrels but I've never seen one on the box. Any help gratefully accepted. Thanks

https://imgur.com/tS8AGrI

https://imgur.com/ZYBHoPw