This year seemed like a perfect opportunity for the brant population to thrive but the only problem was that this fortuitous weather cycle also coincided with a dramatic drop in the lemming population which cycles every 3 - 4 years and which are the other main food source of the Arctic fox. (sciencedaily.com)
Leadbeater's mixture (see below) can be cooked and fed as the other main food source (about 25 % of the diet). (avianexoticsvet.com)
Recently, seagulls in Washington state have started eating their own chicks, for example, because rising water temperatures have caused plankton, their main food source, to vanish. (businessinsider.com)