Question

what may be the relationship between Lake and birds on tree

Answer 1

it must be
the birds want water
for drinking......

Answer 2

It is a food chain, described as – Phytoplanktons  Zooplanktons  Fishes  Birds.

Phytoplanktons growing in pond are food for Zooplanktons. These Zooplanktons are foods for fishes, and fishes are foods for birds. Hence birds are also a part of lake ecosystem.