There could be. The Harry Potter fandom is so large and diverse that it's very likely that someone has written a fanfic with this premise. However, it might not be easy to find. You could also check some Harry Potter - specific fanfic communities on social media platforms. People there might be able to point you in the right direction if they know of any such fanfics.
Well, one interesting aspect is the unique take on Harry's character. Instead of the common animagus forms like a stag or a cat, an owl form gives him different abilities like silent flight and excellent night vision. This can add a whole new dimension to his adventures in the wizarding world.
It could be really cool. Harry could use his owl form to spy on the bad guys secretly. He might be able to fly around Hogwarts at night without being noticed much, gathering information. For example, he could perch on a window ledge of the Slytherin common room to eavesdrop on Malfoy's plans.
I'm not sure about a specific 'harry owl animagus fanfic' right off the bat. But you can start your search on fanfic platforms like Archive of Our Own. Just type in 'harry owl animagus' in the search bar, and you'll likely find a bunch of stories to choose from.
One possible fanfiction could be about Harry's owl, Hedwig, becoming an Animagus. Maybe she could transform into a human - like form to protect Harry in a dangerous situation. For example, when Death Eaters are closing in on Harry, Hedwig could turn into a wizard - like figure and use magic to fend them off.
One idea could be that Harry has to figure out how to communicate with his friends while in owl form. He could use his beak to write in the dirt or something similar. Another plot could involve Harry trying to find a way to reverse the situation while also using his new owl abilities to his advantage, like flying to places he couldn't reach before.
In this fanfic, Hermione would jump into action. She'd make lists of possible causes and solutions. She might consult with other intelligent characters like Luna Lovegood or Professor Flitwick. Ron would be the emotional support for Harry. He'd try to make Harry comfortable in his owl form, bringing him food and making sure he has a safe place to stay. And then there are the other students. Some might be scared of Harry in his new form, while others might be fascinated and want to study him. The teachers would have different reactions too. McGonagall, being an animagus herself, might have some insights but also be strict about the situation, while Trelawney might predict all sorts of wild things about Harry's future as an owl.
One possible fanfic could be 'The Owl Within' where Harry discovers his new form and has to navigate the wizarding world secretly. He might face challenges like hiding from his friends and still trying to fight against Voldemort's forces in his owl form.
Another way to make it unique is to set the fanfiction in a different time period within the Harry Potter world. Instead of the main events of the books, it could be set in the past, like during the founding of Hogwarts. The owl Animagus could play a crucial role in the early days of the school, perhaps helping the founders with their magical tasks or being a messenger between different magical communities at that time. This would give a whole new perspective to the story.
Another plot point could be his interaction with other animagi. Maybe there are other animagi in the story who try to help him figure out how to change back or at least how to better control his owl form. They could teach him things like how to use his owl senses more effectively in the wizarding world.