At the river were two shags on a branch in the water. One is a Pied Shag but a clearly smaller shag was nearby. I think the smaller one is a Kawau tūī | Little black shag 🐦 :

Little black shags are similar in size to little shags, but they lack any white plumage and have a relatively short tail. They are much smaller than black shags.

Two shags on a branch in the river. One is all black and a great deal smaller than the Pied Shag nearby.