how is this considered hiding methods?

[Gor Gyolchanyan]

Can someone please tell me why the following code gives these 
errors?

Error: class main.BirdZoo use of main.VertebrateZoo.take(Animal 
animal_) hidden by BirdZoo is deprecated

Error: class main.ParrotZoo use of main.VertebrateZoo.take(Animal 
animal_) hidden by ParrotZoo is deprecated

/// The code:

	class Animal { }
	class Vertebrate { }
	class Bird: Animal { }
	class Parrot: Bird { }
	
	class VertebrateZoo
	{
		void take(Animal animal_)
		{
			if(auto vertebrate = cast(Vertebrate)animal_)
				take(vertebrate);
		}
		
		abstract void take(Vertebrate vertebrate_);
	}
	
	class BirdZoo: VertebrateZoo
	{
		override void take(Vertebrate vertebrate_)
		{
			if(auto bird = cast(Bird)vertebrate_)
				take(bird);
		}
		
		abstract void take(Bird bird_);
	}
	
	class ParrotZoo: BirdZoo
	{
		override void take(Bird bird_)
		{
			if(auto parrot = cast(Parrot)bird_)
				take(parrot);
		}
		
		abstract void take(Parrot parrot_);
	}