Adding water and landscaping will enhance the number of birds you attract. Many species will gather together after the nesting period is finished. During fall migration, during the winter and through spring migration, there is a certain amount of protection from being in a flock. Food and shelter are easier to find when there are a lot of eyes looking for it and it is harder for a predator to pick an individual out of the crowd. During the nesting period, most bird species have a territory of some size around the nest that they will not allow others of their species to enter and often they will keep out other bird species as best they can.
Some birds also protect a larger feeding territory.
Both territories will reduce the number of individuals and species in your property during this time. The more variety of plants you have in your yard, especially dense areas of shrubs and evergreens, the more nesting territories you will have. The addition of water also will help. More birds may visit your yard than you realize. Many birds, especially the females, look a lot alike.