House martins and swifts like to make their homes high up on tall buildings because it helps keep them safe from danger. You could say:
- They pick tall places to build their nests so they can watch all around and stay safe.
- The birds like the tops of buildings because it feels like a special, cozy home up high.
- They build their nests on tall buildings to hide from animals that might want to bother them.
It's like how you might like to play on a tall slide because you can see everything and feel safe up high!