Blackbirds

Kuroutadori (クロウタドリ, "Blackbirds") are as they are named, blackbirds which can be summoned in a multitude of ways. They could be summoned either by scroll, tattoo, or via hand seals. They can even be summoned from objects depending on if you have planted the 'seal' there.

The summoning contract is owned currently by Onizuki, whom is 'The First' to the Blackbirds and most respected of the summoners or signers of the contract. There is a special way to summon these animals, however, that special way is through a tattoo planted upon the individual's body. In order to received the tattoo, you must receive it from a Blackbird Sage whom or which resides in a highly secret and hidden, as well as consecrated, place in the realm that cannot be found simply by random people. You can only reach it through being reverse summoned there, unless you've learned how to get there or do it yourself 'somehow'.

This species of bird can be summoned in different sizes, from small to large enough to be rode upon. These birds are highly skilled in attack, speed, evasion, and maneuvering; they are quite the respected summoning. Their dark appearance can blend in with the night making them near invisible to normal eyes. Thus, making them perfect for reconnaissance. The summoning is also known for it's special jutsu that allows the summoner to speak through the Blackbird, to another in a different location.

Blackbird Secret Multiplication Seal
The blackbirds have a special seal placed upon each one of them that gives them the ability to multiply when hit with a physical attack, this including Earth Ninjutsu, Wind Ninjutsu (With cutting effect), Water Ninjutsu (With cutting effect), Taijutsu, Kenjutsu, physical-based Fūinjutsu and the like. A major weakness of it however is Fire Ninjutsu, because of it's burning effect that will ensure that the summoning will be gone. When multiplying, they are able to combine with each other once more to make one blackbird, or it can continue to attack in numbers.

Genjutsu
A specialty of the blackbirds is genjutsu, and many genjutsu can be cast through the use of them. Depending on the skill of the summoner they are allowed to animate genjutsu, this way they can, say, make themselves be able to perform advanced jutsus with the crows that is mostly supplementary, few may be offensive.