We can reduce the Direction Random Spread from 20 to approximately 12 to narrow the path and bring a little more organization to our flock.

Do a RAM preview, and see how the flock of red particles is looking. The Velocity of 130 is about right, as is the default value of 20 for the Velocity Random Spread. The Particle Radius will not impact our final composite, so we can safely leave it at two.

For our bird, we used Poser to animate a five-second flapping cycle that is repeated two times for a total 10-second animation. Except for the flapping, the bird remains stationary within the Poser environment. We rendered our solo bird, named Flying Hawk, as an .AVI with a transparency (alpha) channel, imported it into After Effects and dropped it into the top layer of our timeline.

Click on the Bird Particles layer, and, in the effects panel, twirl down the Layer Map property. To the right of Use Layer, select your Flying Hawk layer and, presto, instant flock!

As you can see, we have a lot of birds fighting for some wing room, so let's reduce the Particles Per Second to four. That's better.

Before we put our final touches to this scene, deselect the visibility eyeball of the Flying Hawk.avi layer, as now we want to see only the particle-birds.

Do another RAM preview, and you have a nice flock of birds...doing exactly the same thing. Not particularly realistic. So let's adjust two more properties. Go to Layer Map>Use Layer>Time Offset Type, and select Relative Random. Just under this, change the Random Time Max to .9 or whatever value looks best for your scene. You may need to move your Cannon off screen to the right, so that this new setting does not start popping on birds within your viewable frame. This setting will also shorten your usable scene length. The scene now begins emitting your particle-birds at slightly different points in their animations, giving the impression of each being a unique flyer.

Now that you have the basics, you might want to experiment with the Repel Force. Keep the value below one, and watch how the particle-birds now interact with each other. The effect is not what you might see in most flocks of real birds, but it is a powerful parameter you can control for other types of particle effects. The remaining three properties of Wall, Persistent and Ephemeral Property Mappers control advanced features that integrate use of masks and image maps that give you practically an unlimited amount of control - for another tutorial, or two.

Contributing editor Brian Peterson is a video production consultant, trainer and lecturer.

Click here to download the files used in this tutorial.
View the finished effect here.