The birds are Hawk and Falcon respectively.
Explanation:Descending is represented by a negative
A bird descending 15 feet = - 15feet
We are to pick birds that descended less than 15 feet. This means numbers less than -15 would be considered.
On a number line: the bigger the negative number, the lesser the value of the number.
-13 feet > -15feet
-21 feet < -15feet
-11 feet > -15feet
-17 feet < -15feet
-14 feet > -15feet
The altitude less than -15 feet are -21 feet and -17 feet
The birds are Hawk and Falcon respectively.