Hippos are well adapted for staying in water for long periods of time. Their eyes, ears, and nostrils are located high on their heads so they can remain submerged while allowing these organs to function above the waterline. Their skin also secretes an oily red substance that protects against sunburn and keeps the skin moist. This allows hippos to spend most daylight hours partially submerged in rivers and lakes to stay cool in the hot African climate. But just how long can they actually stay underwater if needed?
Quick Summary
Hippos can stay submerged underwater for up to 5 minutes at a time before needing to come up for air. They are natural swimmers and float easily, allowing them to rest underwater with little effort. While 5 minutes is the average, hippos have been recorded staying underwater for up to 30 minutes in rare circumstances. Their barrel-shaped bodies and natural buoyancy allow them to conserve energy while submerged.
How Do Hippo Lungs Work Underwater?
Hippos have specially adapted lungs that allow them to remain underwater for several minutes at a time. Here’s how their lungs work:
- Large lung capacity – Hippo lungs can hold more air than other mammals relative to their size. This provides more oxygen reserves.
- Efficient oxygen use – Hippo bodies are designed to extract oxygen from the lungs efficiently. Less oxygen is wasted when submerged.
- Slow heart rate – A hippo’s heart beats slowly underwater, further conserving oxygen supplies in the bloodstream.
- Blood vessel adaptations – Blood vessels automatically restrict blood flow to non-essential organs when underwater. This preserves oxygen for the heart and brain.
These adaptations allow hippos to make the most of the oxygen stored in their large lungs. By slowing their metabolism, they can stretch a single breath of air for several minutes.
Buoyancy and Resting Underwater
Another key factor in a hippo’s ability to stay underwater is their natural buoyancy. Hippos have barrel-shaped bodies with very high fat content. This fat content makes them float more easily with less effort:
- Fat is less dense than water, so it provides natural buoyancy.
- The hippo’s rotund shape acts like a floatation device.
- Their short, sturdy legs don’t sink their bodies when resting.
Hippos often rest fully submerged, allowing them to float with little physical exertion. Their buoyancy lets them conserve energy while avoiding the sun’s heat at the surface. They can rest in this state for over 5 minutes without issue.
Breath Holding Reflex
Hippos also possess an adaptive breath holding reflex when underwater. When submerged, their bodies automatically respond by:
- Slowing the heart rate to conserve oxygen.
- Constricting blood vessels to prioritize oxygen delivery to the heart and brain.
- Lowering muscle activity and metabolism to use less oxygen.
This breathing holding response allows hippos to get the most out of their oxygen reserves. It kicks in even when resting underwater, maximizing their breath holding time.
Maximum Underwater Time
On average, hippos can hold their breath underwater for 5 minutes before resurfacing. However, they have been recorded staying submerged for up to 30 minutes in rare situations!
In a 2012 study, hippos were observed holding their breath for up to 29 minutes while resting underwater. This happened during deep sleep at night when their metabolism was already lowered. 30 minutes appears to be the absolute maximum hippos can endure when resting in ideal conditions.
During the day when active, most hippos resurface to breathe every 1-5 minutes. Calves and juveniles surface more frequently than adults. 5 minutes is the typical maximum for daytime submersion while active underwater.
Surfacing Behavior
Hippos most often resurface to breathe without leaving the water completely. They just poke their nostrils out of the water to take a breath. Their ears and eyes remain submerged since they are high enough on the head to function underwater.
When hippos do fully emerge onto land, it’s usually to bask and regulate their body temperature. After basking, they will often enter the water again even without having to breathe. Their ability to hold their breath for so long gives them flexibility in surfacing patterns.
Underwater Movement and Foraging
While hippos don’t swim constantly like fish, they are well adapted for getting around underwater:
- Their natural buoyancy helps reduce the effort to move underwater.
- Powerful backward-facing hind legs propel them through the water when needed.
- Their eyes and ears are positioned to function while submerged.
This allows hippos to walk along the bottom of riverbeds and lakes while looking for food. They can forage underwater for food sources like aquatic plants for several minutes at a time before resurfacing.
Breathing Challenges for Hippos
Despite their impressive breath holding abilities, hippos do face challenges when coming up for air:
- Being so heavy makes it difficult to float vertically to breathe if they are resting on the bottom.
- Limited mobility on land means they try to stay in water as much as possible.
- If threatened on land, they may not be able to reach water quickly to submerge.
To overcome these issues, hippos tend to stay in relatively shallow water where they can stand. They may also choose sloped locations they can walk up to breathe with less effort. Dominant males occupy the best pools that allow easy access to air.
How Long Can Hippo Calves Stay Underwater?
Newborn hippo calves have not yet developed the underwater endurance of adults. They have smaller lung capacity and less body fat for buoyancy. As a result, calves cannot stay underwater for more than 2-3 minutes at a time.
Calves must surface more frequently than adult hippos to breathe. They stay close to their mothers for protection in their early months. By 1 year old, juvenile hippos can hold their breath for 4-5 minutes as their bodies develop.
Record Breaking Hippo Dives
While most hippos don’t approach their maximum breath holding duration very often, there are some record-breaking hippo dives:
- In 1955, a hippo was recorded staying submerged for 31 minutes after being chased into a pool in Africa.
- A hippo named Donna at the Mesker Park Zoo was recorded staying underwater for over 5 minutes while resting on the bottom of her pool.
- A hippo named Bertha at a zoo in Switzerland managed to stay underwater for a remarkable 18 minutes by floating motionless near the bottom of her pool.
These elongated breath-holding sessions only happen in rare situations that require extreme stillness and very slow metabolism. But they demonstrate the incredible capabilities of the hippo’s unique diving physiology when tested.
Why Can’t Other Animals Match the Hippo’s Diving Abilities?
Many aquatic mammals like whales and seals can stay underwater for longer than hippos. But when comparing similar amphibious mammals, the hippo stands out:
| Animal | Max Submersion Time |
|---|---|
| Hippo | 30 minutes |
| Elephant | 2-3 minutes |
| Rhino | 2 minutes |
| Gorilla | 30-60 seconds |
The hippo has unique adaptations that allow it to outlast all other amphibious mammals underwater:
- Large lung capacity and efficient oxygen use.
- Natural buoyancy from their high fat content.
- Adaptive blood vessel and heart rate changes.
- A tendency to rest in water instead of actively swim.
This combination of traits gives hippos an advantage for holding their breath compared to related species. Their impressive breath holding abilities are a major reason they remain confined to their aquatic habitats.
Conclusion
A hippo’s ability to stay underwater for over 5 minutes on average gives it great flexibility in aquatic environments. While 1-5 minutes is typical, hippos can remain submerged for over 30 minutes with preparation when conditions are ideal. This breath-holding advantage allows hippos to live and forage in the water for most of their days.
Unique lung adaptations, natural buoyancy, and low exertion floating allow hippos to make the most of their oxygen reserves underwater. While calves and juveniles can’t match adult durations yet, they still exceed the breath holding limits of almost all other land mammals. The hippo’s incredible diving abilities are key to their amphibious lifestyle in the waters of Africa.
