{{This article was posted on December 5, 2018. Lost and found, it is reposted here.}}
12 years ago when some people bought the land next to my house they built a really big wall along the border.
While standing of my roof, mainly during the sunbathing winter months, I got to staring at the wall.
The wall had a quite a few gaps in the bricks and slowly sparrows starting living in them. It reached a point where every gap was occupied and lots of lots of sparrows could be seen. then the bredding season came and most gaps had chicks. But crows from the trees nearby started attacking and taking away the chicks. I witnessed, pretty much helplessly, quite a few struggles between crows and sparrows. Most often the crows got better of the sparrows and took chicks away.
Slowly many of the gaps got empty as sparrows started moving out due to the danger. It got to a point where most of the gaps were empty, except for a few. Some of the sparrows struggled on and during the course of years the population started to blossom pretty well.
While gazing at the wall, I noticed that many chicks started hatching and population became pretty big. Most amazing was no crows were attacking the nests anymore.
Being the curious kind I went looking around to what had happened. How things were working out for the sparrows, inspite of all the crows still living in the trees nearby.
I started by looking at the gaps and number of sparrows. Noticeable change was that the number of gaps occupied had decreased to quite a few. Gaps, there were near the ground not occupied previously, were now occupied. Gaps that were near power lines were occupied more, where the power lines would work as deterrants to the sparrows.
On closer observation I found the structure of the gaps occupied were different. All the gaps that were straight inside were unoccupied. All gaps that had some sort of brick pieces jutting out on the inside were occupied more and more and the most precious gaps were ones with jutting inside with plant growing on the outside and power lines very close to the wall. I could see that the biggest fighters among the sparrows occupied these premium sites. The gaps occupied were only the ones that crows could not absolutely put their beaks inside.
Clever birds!!!… Evolution at work.