Geese are not mammals, they are birds. In general, mammals have fur and not feathers and do not lay eggs. Birds also have hollow bones that allow them to take flight with ease and have beaks with no teeth.
Geese have a few shared traits with mammals, but they are definitely birds.
In this article, we’ll learn what makes a bird a bird and what makes a mammal a mammal, and look at some of the characteristics of geese that explain which category they fall into.
Geese are birds and not mammals. The main things that separate them from each other are that geese have feathers, whereas mammals generally have fur. It’s also true that mammals can’t fly, either.
Of course, there are always a few exceptions to any rule in the animal kingdom. In this case, it is the bat. Though a mammal, the bat has wings and is perfectly capable of flight.
Why Aren’t Geese Considered Mammals?
There are actually quite a few things that separate mammals from birds. The difference doesn’t solely come down to which animals can fly and which can’t, although that’s definitely a consideration.
Here are some of the characteristics of geese that conflict with what we would expect to find in a mammal.
1. Geese Have Feathers
In general, we tend to have a pretty good idea of what makes a bird and what makes a mammal. Perhaps the most obvious visual indicator is that birds have feathers and mammals have fur or hair.
Fur and feathers are both used for thermal regulation, but feathers are also used for flight.
2. Geese Don’t Produce Milk
The term mammal shares an important etymology with the mammary glands found in all mammals. Every mammal produces milk for their young, hence this is a defining feature of all mammals.
Since geese don’t have mammary glands, they can not produce milk and thus are not considered mammals.
Since they can’t make milk, geese feed their young with easily digestible food instead.
3. Geese Don’t Give Birth to Live Young
Another reason that geese aren’t considered mammals is that geese lay eggs, whereas most mammals give birth to live young.
There is one category of mammals called monotremes, that is the exception to this rule. Monotremes are aquatic mammals such as platypuses that lay soft-shelled eggs.
Since geese lay hard-shelled eggs, they are not considered mammals.
4. Geese Have Hollow Bones
It may sound a little unusual, but geese do have hollow bones. Over time, birds have evolved to have lighter and lighter bones, enabling them to maintain flight more efficiently. The main limb bones of most birds are hollow.
This is especially important for heavy migratory birds like geese, where the effect of a small energy saving is vastly multiplied over their several thousand mile migration trip.
By contrast, mammals bones are designed to be strong and are mostly solid with few exceptions.
Read More: How High can Geese Fly?
Why are Geese Considered Birds?
Birds are quite well defined by the scientific community. When we compare the key elements that make a bird a bird, we find that geese comfortably meet the definition.
Some of the main features that define a bird include:
- They have feathers
- They have beaks with no teeth
- They lay hard-shelled eggs
- They belong to the Aves class of animals
- They have a fast metabolism
Let’s look at each of these in more detail and see how they apply to geese.
1. Birds Have Feathers
Birds have feathers to keep themselves warm, and to assist with flight. Although geese fly south for winter, their warm down feathers help keep them warm in summer when they spend a few months in the high arctic.
Since geese have feathers, they are considered birds.
2. Birds Have Beaks with No Teeth
Another defining trait of birds is that they have beaks with no teeth in them.
Though it may look like geese have teeth, they are not true teeth in the same sense that a mammal has teeth. Geese teeth are made from hard keratinous cartilage, the same material as their beaks.
Read More: Do Geese have Teeth on their Tongues?
3. Birds Lay Hard-Shelled Eggs
One of the defining characteristics of birds is that they lay hard-shelled eggs. Unlike reptiles who lay soft eggs, or mammals who (mostly) give birth to live young, geese lay hard-shelled eggs that need to be incubated, similar to other birds.
4. Birds Belong to the Aves Family
Geese, are from the Aves class of animals. All animals in this classification lay eggs, have warm blood, and stand on two legs. The Aves class is home to every animal that we would consider a bird, from the tiniest hummingbird to the largest ostrich.
By contrast, all mammals belong to the Mammalia class of animals.
5. Birds have a High Metabolism
Birds have a much faster metabolism than mammals do. To make digestion possible without a large intestine, geese will often swallow small pebbles that will then grind up the food in their stomachs.
This special digestion system (called a gizzard) is common in birds and helps keep them light enough to make long flights.
Just to confuse things a little, there are some mammals that are capable of flight. The most well-known flying mammals are bats, who are capable of sustained flight.
There are also some mammals like sugar gliders and flying squirrels who can glide through the air but can’t really fly.
The bat is quite similar to a goose in that it has warm blood, can fly, and has a skeleton. However, bats do not belong to the Aves class of animals and thus are not birds.
When you look at a bat a little more closely, it’s obvious why it’s a mammal. Bats have mammary glands and feed their young milk, they have fur and not feathers, and they give birth to live young.
To sum up, geese are not considered mammals because they are birds, and mammals and birds belong to two separate and non-overlapping classes of animals called Aves and Mammalia.
Geese have several characteristics that make it clear they belong to the bird family, including laying hard-shelled eggs, having a covering of feathers, having hollow bones, and having beaks with no teeth.
Stuart is the editor of Fauna Facts. He edits our writers’ work as well as contributing his own content. Stuart is passionate about sustainable farming and animal welfare and has written extensively on cows and geese for the site.