This is a study in the Red-Vented Bulbul, kind of........
The Red-vented Bulbul is easily identified by its short crest giving the head a squarish appearance. The body is dark brown with a scaly pattern while the head is darker or black. The rump is white while the vent is red. The black tail is tipped in white. I found this information here.
On doing a little research I found it was introduced from India in the 1950's or 1960's, and was an illegal cage release, for what reason I am not sure. I also read it's distribution is only on Oahu.
This bird is very common and is a noisy garden pest. It eats orchid bulbs as well as many types of fruits. In 1989 it caused an estimated $300,000 in damage to the orchid industry on O‘ahu. Bulbuls also are aggressive and are probably displacing many native birds.
What a shame, like our Sparrows, Grackles and Starlings, it has a bad reputation but I found it a pretty little bird and very interesting because I had never seen it before. And just like the tiny Sparrow and his like-wise friends, I can't help but feel a certain sympathy for them. It was after all not their fault that man decided to play with Mother Nature.