Today was exciting. First, IA and IB were duetting, see attached video. Duetting is a form of communication where one bird initiates a call, IA in this instance, and another one, his sibling IB, answers. This form of song is useful if the birds cannot see each other and want to establish visual contact. In this case IB sat in a tree nearby, just out of view of IA, who was perched on a chair in the garden. The siblings duet regularly, and it may also function as a way to reinforce bonding between the two birds.
Duetting is a sequential song. If birds sing at the same time then this is referred to as carolling.
Carolling is usually harsher and is used to reaffirm territorial ownership. This happened today as well, but later in the afternoon, when I suddenly heard a lot of calling and saw wings flapping in the garden. On closer inspection I found that two large magpies had intruded on the family's territory, and were dive-bombed by the adults in the garden.
By the time I grabbed a camera and started shooting a video, the magpie family sat on the power line and it started to rain shortly thereafter. The siblings stayed close together throughout, with IA flying off from the power line last, already drenched. One of the adults held the fort just a little longer, sitting on the fence, and looking at the intruders who carried on foraging in our neighbour's garden quite unperturbed, before flying off to join the rest of the family.