If you live in Florida, it is illegal to feed them; if you live anywhere else, it may or may not be illegal, but it is not a good idea to feed them.
This is from Florida, but it can apply to just about anywhere:
Q: I live on a golf course in Hobe Sound. I have sandhill cranes as guests once in a while. I would like to offer my hospitality by giving them a treat they would enjoy and be healthy for them. They are a magnificent bird. Kind of loud. Please advise if you have a suggestion as to what I can offer. Thank you -- Barry
A: I appreciate your eagerness to give the sandhill cranes a healthy treat. But, Barry, the best thing to feed sandhill cranes is -- nothing.
The Florida Fish and Wildlife Conservation Commission passed a restriction on feeding wildlife -- including sandhill cranes -- effective May 2002. People who are caught feeding these birds and other animals can face steep fines and jail time.
You are lucky to have sandhill cranes in your neighborhood because they are magnificent birds and a delight to watch. But feeding these 4-foot-tall birds isn't the same as putting seed in a feeder for the little birds that come to Florida for the winter. Many sandhill cranes live in Florida year-round and are able to find their own food.
In fact, if you look at past Q&As on this page (look under the heading "Wildlife and Birds"), you will read about sandhill cranes that have become a nuisance and begun destroying property because they got too used to being fed by people and are asking for their snack by trying to get attention! What you won't read in any of the Q&As are some of the e-mails I get from people who want to know how to "get rid of" pesky animals -- animals that have become too forward with people because they have learned that some people give them food. Believe me, there are communities all over Florida where people are upset that a neighbor has fed an animal or a group of animals that hang out, make noise and destroy property, and when an animal's behavior gets so bad that it becomes a community-wide problem, the community becomes a lynch mob out to get the offending critter. And it all could have been prevented if the animal just wasn't fed in the first place.
Many animals are cute and special, but it is never a good idea to feed wild animals of any kind. Once wild animals become used to expecting food from people, they lose their natural fear of people. This fear is healthy and protects them from people who may be up to no good. (I once saw a raccoon who'd gotten used to being fed by people accept a lit cigarette from a passerby. The raccoon was expecting food -- instead, it got burned.) When animals start getting aggressive about their handouts, people sometimes get annoyed or frightened, and then what happens is that animal-control authorities come to relocate the animal (which doesn't work for every species), or they destroy the animal (because the animal threatens people's lives, which is usually the case with predators like alligators).
Also, animals that have learned that people will feed them no longer look for food themselves, and their health declines because they don't eat the foods they naturally would eat.
So I hope you can see that feeding wild animals ultimately results in their downfall. If you really love wildlife, the best thing to do is let them stay wild so they can live their lives as they should -- naturally.
There are ways you can help animals other than by feeding them, though. You can volunteer with a local park (like nearby Jonathan Dickinson State Park or Hobe Sound National Wildlife Refuge), plant native Florida plants (which provide native wildlife with food and shelter) in your backyard or neighborhood park and get involved with organizations that protect wildlife.
Enjoy watching your special sandhill cranes!
Quoted directly from http://www.ecofloridamag.com/askeditor_feeding_wildlife.htm
If you would like to plant things to make your property more inviting to the cranes, check out this website: http://www.twingroves.district96.k12.il.us/Wetlands/Crane/CraneFood.html
It states: Sandhill Cranes have a diet that changes depending on the season. They are omnivores. That means that they eat both plants and animals. They eat mostly plants with waste corn making up about 95% of their diet. While migrating through Nebraska they eat an average of 1,600 tons of corn, building up their fat to hold them through the winter nesting season. The other 5% of their diet consists of worms, insect larvae, snails, and other small invertebrates. They eat snakes, frogs, mice, crayfish, salamanders, and other animals that they can find in the muddy waters of their habitat.
When a crane catches an animal that isn't too large, like the mouse, it eats it all in one gulp. On the other hand, with the larger animals, like the salamander, it pecks it into little pieces. Then, the crane eats the smaller pieces.
The Sandhill Crane also eats berries, tubers, seeds, and roots. Plus, they eat many grains such as wheat and barley.