Particle systems can be used to create dynamic animation, or to help with repetitive tasks. They can also be used to add a sense of randomness that is hard to produce on a computer. Groupings of animals can be hard to produce without seeming contrived. Random positioning and animation can be achieved quickly with fewer steps using particle emitters and the parametric controls they possess.
Create your scene in 3D Studio Max. Place your lighting, cameras and atmospheric effects. Import your bird model into the scene. Collapse the modifier stack of your bird model.
Create a particle system. Open the Particle Systems menu found in the primitives pull-down menu. Click the PCloud button. In the overhead view, left-click and drag a square defining the length and width of the particle cloud emitter. Release the left mouse button then drag again to define the height of the particle emitter, then left-click once more.
Open the modifier panel with the PCloud selected. Right-click the Pcloud001 box and rename it "Flock." In the Parameters dialogue open the Particle Type window and select Instanced Geometry. Scroll down to the "Instancing Parameters" window and left-click the "Pick Object" button. Click your bird model to attach it to your particle system.
Adjust parameters such as "Animation Offset Keying" to keep the birds from flapping their wings in unison. Because the model is instanced, your original model will be exactly what is reproduced for each bird, including keyframe animation. Use variables as well as particle-affecting objects to add more realism to the way your flock moves and to add a greater sense of randomness.
Carefully change variables so that you don't have birds disappearing or appearing during any animations using this technique. You will have to adjust birth, life and emitter start/stop times to keep your birds from disappearing or appearing.