Trying out ES6 classes, I think I made a mistake somewhere...

classes.js

class Animal {
  constructor(name="Unnamed", age=0, height=0) {
    this.name = name;
    this.age = age;
    this.height = height;
  }
  describe() {
    return `Species:\t${this.constructor.name}\nName:\t${this.name}\nAge:\t${this.age}\nHeight:\t${this.height}`;
  }
}


class Mammal extends Animal {
  constructor(name="Unnamed", age=0, height=0, hasFur=true) {
    super(name=name, age=age, height=height);
    this.hasFur = hasFur;
    this.warm_blooded = true;
  }
}


class Cat extends Mammal {
  constructor(name="Unnamed", age=0, height=0) {
    super(name=name, age=age, height=height, hasFur=true);
  }
}


class Whale extends Mammal {
  constructor(name="Unnamed", age=0, height=0) {
    super(name=name, age=age, height=height, hasFur=false);
  }
}


class Human extends Mammal {
  constructor(name="Unnamed", age=0, height=0) {
    super(name=name, age=age, height=height, hasFur=false);
  }
}


let josh = new Human(name="Josh", age=19, height=192);
console.log(josh.describe());