Did your kids bring home bird feeders last Friday? Mine, too. Did you put them out? Me niether.
Some amature internet research reveals that there was once an actual custom in some European communities to put out food for the birds on Shabos Parshas Bshalach. In our day, the custom seems to be something else involving school crafts and good intentions.
The official reason for the custom is a Mechilta which describes an evil plot to embaress Moshe that was foiled by the birds. To say thank you, our ancestors put out crumbs. Though I rather doubt this is the true source of the custom I must admit that I have not been able to find a shred of evidence in support of my skeptism.
Search for more information about [topic] at 4torah.com.