I've tried about 15 times to land any hit on the roaming articuno in Platinum but every time it flees before I can attack. The other two birds weren't any issue, so is this an intentional game aspect or am I incredibly unlucky?
Articuno outspeeds your Pokémon, so it’s able to go first. In this case, it flees.
Try levelling up your Pokémon some more or lead with a Pokémon with high speed. You could also use priority moves to get around this.
Hope I helped!