The Maori Stutter

I don't know why, but Maori seems to repeat everything. Here are a couple place, plant, animal names:
Pukapuka
Pekapeka
Pekepeke
Huhu
Kaka
Ongaonga
Rewarewa
Tiritiri
Mingimingi
And it goes on and on. I'm sure there is a good reason, but I don't know it.