Answer:
Less food means less bird, solely because there is less food to go around, so not a lot of them will survive with the lack of it. The habitat with regain food eventually but it will take a while.
4 will be effected by vegetation growing more because there will be less birds to trample/eat it
3 will be effected by more water supply for the other animals because the birds won't be there to drink it.
2 wont have as many birds and will be effected by starvation
1 will become skinnier or die.
