In addition to listening for your cat, you should keep an ear out for bird alarm calls during the search for your lost cat. Song birds make a variety of sounds including songs, calls and alarms. They use alarm calls to warn other birds about potential threats such as predators. Some even have different alarm calls to indicate whether the potential predator is on the ground or in the sky. If your cat is hiding in a bush or stuck in a tree, birds may surround your cat and make alarm calls.
In the video below, Jon Young, describes how birds position themselves around a cat when alarm calling. This particular cat is stalking, so the bird pattern and alarms will move. With an escaped indoor-only cat that is hiding in fear or a cat stuck in a tree, the alarm call location will be fairly static.
The most effective method for listening for bird alarms calls is to just sit and listen in your own yard. You can also listen when searching your neighbor's properties. However, be aware that birds may also make alarm calls if disturbed by human activity. You are more likely to cause bird alarm calls by walking through dense vegetation or wooded areas. A safer way to check the woods is walking along open areas along the woods edge or at least staying on trails.
You can find a list of bird alarm calls on the Bird Language site. Scroll to the bottom of the page for a list of recorded bird alarm calls. If you aren't familiar with the birds in your area, some common species to check in the US include the American Robin, Dark-eyed Junco, Northern Cardinal, Hermit Thrush, Black-capped Chickadee, and Northern Mockingbird. You really don't need to memorize the calls. If you listen to a few of them, you will find that the nature of the calls are fairly similar. An alarm call is often a series of loud, repeated notes. For comparison, listen to a few of the bird songs, which have more of a melody and take longer to repeat.
Example Bird Alarm Calls
American Robin Alarm Call
Northern Cardinal Alarm Call
Mockingbird Alarm Call
Wren Alarm Call
Crows and Jays have loud distinct alarm calls. However, these types of birds also tend to make these calls for many reasons besides alarms. Crows may mob a cat stuck up in a tree, so loud cawing is still worth checking out to see if it has a cause.
Squirrel and Chipmunk Alarm Calls
Squirrels, chipmunks and other small mammals also use alarm calls. The Bird Language site includes alarm calls for several species of squirrels, chipmunk, and a few other small mammals. Be aware that squirrels and chipmunks also use their alarm calls on humans. So if you disturbed them during your search, they may be chirping at you. In my experience, squirrels and chipmunks are often within sight of a cat, but not nearly as close as birds. They may also pick up an alarm call from another squirrel, chipmunk or bird without being near the perceived threat.
Gray Squirrel Alarm Call
Chipmunk Alarm Call
Don't Forget to Listen for Your Cat Too
Most cats will not meow when lost but some will, so be sure to take some time to stop and listen during your search. Don't get tricked by the cat bird, which has a call that sometimes sounds like the mewing of a cat.
Cat Bird Call
References and Suggested Reading
Bird Language Audio Library - site founded by Jon Young. Includes examples of songs, calls and alarms for many North American birds.
Young, J. and T. Morgan. 2007. Animal Tracking Basics. Stackpole Books. 305 pages.
Young, J. 2013. What the Robin Knows: How Birds Reveal the Secrets of the Natural World. Mariner Books. 272 pages.