Accessing Named Routes in Rakefile

I have some named routes like this rake routes:

birthdays GET    /birthdays(.:format)                             birthdays#index

In a rakefile I simply want to be able to call birthdays_url like I would in my view.

task :import_birthdays => :environment do
  url = birthdays_url
end

But I'm getting an error undefined local variable or method 'birthdays_url' for main:Object