Despite their general similarities, male and female Bar-tailed godwits/kuaka are sexually dimorphic sufficiently to easily differentiate in the field, whether in breeding plumage, or not.

Prior to migrating north for breeding the males begin to develop their rich colouration which is the most obvious way to differentiate them from the female.

The other obvious way to separate the sexes is size and bill length. The males are smaller with an average of only 2/3 the weight of the female, 275-400 g (male); 325-600 g (female). For me, the simplest differentiator though is bill length. Females have a significantly longer bill with which they are able to forage deeper into the mud layers.

This next photo taken shortly after the above shows the birds together with the male clearly smaller even though closer to the camera.

This next photos shows a pair at rest and shows the relative size difference as well as plumage difference in breeding colours.

With a little practice you can soon identify the sexes in the field based on bill length even when they are not in breeding plumage.

Photos at Pūkorokoro/Miranda with Nikon Z9 and Nikkor Z 800mm f6.3 VR S