Here you are creating a new array (with the map array method) and then pushing that newly created array into the lowerCase array. So you're making an array of objects nested inside of another array, like this: [ [{'property': 'value'}] ] when it should just be an array of objects, like this: [{'property': 'value'}].

To resolve this, just assign the newly created array to the lowerCase variable, instead of pushing the newly created array into the array assigned to the lowerCase variable. Here is an example (I'm also using arrow notation), please let me know if you have any questions:

const lowerCase = zooAnimals.map(zooAnimal => zooAnimal.animal_name.toLowerCase()); 

While you are logging out the correct values here, the request is for you to create an array of the values that you are logging. Currently, you're just logging out a single string every time your forEach method loops. Then, when you log out the animalNames array with console.log(animalNames) you are logging out an empty array [].

The correct way to do this, is by using the push array method. Here is an example (using an arrow function), please let me know if you have any questions:

const animalNames = [];
zooAnimals.forEach(zooAnimal => {animalNames.push(`Name: ${zooAnimal.animal_name}, Scientific: ${zooAnimal.scientific_name}.`)})
console.log(animalNames);

Similar to the above lowerCase issue, here you are creating a new array (with the map array method) and then pushing that newly created array into the largerPopulation array. So you're making an array of objects nested inside of another array, like this: [ [{'property': 'value'}] ] when it should just be an array of objects, like this: [{'property': 'value'}].

To resolve this, just assign the newly created array to the largerPopulation variable, instead of pushing the newly created array into the array assigned to the largerPopulation variable. Here is an example (I'm also using arrow notation), please let me know if you have any questions:

const largerPopulation = zooAnimals.filter(zooAnimal => (zooAnimal)=>zooAnimal.population < 5)); 

Using push is fine here, but it is better to assign the value directly to populationTotal like:
const populationTotal = zooAnimals.reduce(function (sum, current) {return sum + current.population},0).

This is because an array is meant to hold a collection of values, whereas your reduce function is reducing down to and returning only a single value. Pushing that single value into an array is unnecessary.

While you've partially done this stretch goal correctly (great job!), this isn't really a CubeMaker. It's another CuboidMaker. The biggest difference between a Cube and a Cuboid is that all the sides of a Cube are the same length, but a Cuboid can have sides of different length. As such, a CubeMaker would only take one argument, as all of the sides would be equal to that one argument. Here is an example, please let me know if you have any questions:

class CubeMaker extends CuboidMaker {
    constructor(length){
        super(length);
        this.length = length;
        this.width = length;
        this.height = length;
    }
    volume() {
      return Math.pow(this.length, 3);
    }
    surfaceArea() {
      return 6 * Math.pow(this.length, 2);
    }
}
const cube = new CubeMaker(5);

Also take note of how the volume() and surfaceArea() methods are different.