This recording is from two ‘lewies’ having a falling-out about access to the flowers on one of our citrus trees. The majority of bickering and fighting behaviour (and calls) I observe in songbirds are concerned with either access to resources (food or the bird bath) or access to breeding partners.
Research indicates that birds are more motivated to engage in defensive (guarding) behaviour around food resources when the resource is neither very scarce nor very abundant. If scarce, the energy spent fighting off hungry (and VERY determined) competitors will likely be greater than that enjoyed from consuming the food. If too abundant, the resource is likely to be so widespread that if a ruddy-great hulking competitor turns up in YOUR bush, you can just as easily move to the next bush and gorge yourself stupid there.