The pair of Magpies must be around the egg laying stage. Only the female Magpie incubates, while her partner must feed her during this time. Females start begging for food to her partner around the time that they lay their first egg, noisily, wings flapping and uttering what has been described as the 'clear call'. The success of a pair of Magpies depends on how good the male is at keeping his mate well fed. A hungry female is more likely to take breaks from incubation, leaving the eggs exposed to predators (most likely Carrion Crows, according to T.R. Birkhead, the archenemy of Magpies).
Yesterday afternoon, I heard this peculiar Magpie call repeatedly from the garden. The pair of Magpies were at a birch tree and one of them (the one on the top, likely the female), flapped her opened wings, chasing and begging to the other, quite indifferent, individual, likely to be the male. I took a video of this behaviour you can watch below (you might need to turn the volume up to hear the call).