Ask Mr. Smarty Plants

Prunus caroliniana (Carolina laurelcherry), according to the Merck Veterinary Manual has cyanogenic glycosides that are transformed into hydrocyanic acid (HCN), also known as prussic acid, in wilted leaves, bark and twigs. This can occur when the cyanogenic glycosides are hydrolyzed by ß-glycosidase or when the cells are mechanically disrupted by freezing, breakage, chewing, etc.  This is especially dangerous for grazing animals such as goats, horses, cows, etc., who may eat these plants or fallen leaves of these plants when other forage is scarce.  Ruminants are especially susceptible because the microbes in their rumen is also responsible for freeing more cyanide.  You can read about the effects of Cyanide Poisoning from the Merck Veterinary Manual.

Obviously, birds do eat the berries with no ill effects and chickens are, indeed, birds.  Birds don't, however, digest the hard seeds.  They expel them and that's how we get so many shoots coming up all over the place.  You could probably eat the fruit yourself as long as you spit out the seed.  You probably wouldn't enjoy it very much because it is reported to be mostly skin and very little 'flesh' and, unless the fleshy part is ripe and soft, it has a bitter taste.  Indeed, all Prunus spp. (peaches, plums, apricots, cherries, wild almonds) have toxic leaves and seeds; but, obviously we enjoy their fruits.  We are safe as long as we don't eat the seeds, bark, leaves or twigs. An exception are cultivated domestic almonds that have a genetic mutation that keeps them from producing cyanogenic glycosides in their edible seeds, the almond.  If your chickens were to eat the leaves of the laurelcherry, however, it might be a different story.  Prunus caroliniana (Carolina laurel cherry) isn't on this list of Plants Toxic to Poultry, but that doesn't guarantee that the leaves are safe for chickens.

You might like to consider some other evergreen California native for your hedge.  Here are a few suggestions:

Malosma laurina (laurel sumac) and here are photos and more information.

Morella californica (California wax myrtle) and here are photos and more information.

Comarostaphylis diversifolia (summer holly) and here is more information.

Ceanothus arboreus (feltleaf ceanothus) and here are photos and more information.

Ceanothus thyrsiflorus (blueblossom) and here are more photos and more information.