Hummingbirds are recognized by their remarkable speed and ability to hover, feats that require an extraordinary amount of energy. They possess one of the highest metabolic rates of any homeothermic animal, requiring a constant supply of fuel for survival. To support rapid movements, including a heart rate that can exceed 200 beats per second and wing-flapping rates up to 99 beats per second, they must consume a massive amount of food daily, often eating up to three times their body weight in nectar and insects. This intense energy demand means they are constantly seeking their next meal. This blazing metabolism presents a unique challenge when the sun sets and food sources become unavailable, raising the question of how they survive the long hours of the night.
The Diurnal Lifestyle
Hummingbirds are strictly diurnal, meaning their entire life cycle and feeding patterns are built around the hours of daylight. Their foraging is entirely dependent on the presence of open flowers and high visibility, which allows them to locate and access the nectar that is their primary energy source. The immense energy required for flight, particularly the sustained hovering unique to this group of birds, cannot be maintained without a continuous caloric intake. They are incapable of sustained activity after dark simply because they would quickly exhaust their energy reserves.
This high-speed, daylight-dependent existence is why they must feed every 10 to 15 minutes while they are awake. Consequently, when the sun dips below the horizon, the hummingbird must immediately cease all energy-intensive activity. The bird must find a sheltered perch, as any attempt at a typical night’s sleep would deplete its reserves before morning.
Surviving the Night Through Torpor
Since they cannot eat or sustain their normal high-speed metabolism during the night, hummingbirds employ a biological survival mechanism known as torpor. Torpor is a deep, temporary state of controlled hypothermia and metabolic slowdown that is distinct from regular sleep. This state is entered voluntarily to conserve the precious fuel stored from their daytime feeding.
The physiological changes during torpor are profound and allow the bird to drastically reduce its energy consumption, sometimes by as much as 95%. A hummingbird’s normal body temperature, which is around 105°F (40.5°C), can drop by almost 50 degrees, sometimes approaching the ambient air temperature. In certain high-altitude species, body temperature has been recorded as low as 3.3°C.
The heart rate slows dramatically, dropping from a rapid 500 beats per minute or more down to fewer than 50 beats per minute. Breathing also becomes intermittent and shallow, sometimes ceasing briefly. This suspended animation allows the bird to survive a period of many hours without food, effectively slowing their biological clock to a crawl.
Entering torpor, however, carries inherent risks, including increased vulnerability to predators due to the bird’s inability to react quickly. Arousing from this deep state is a slow process, sometimes taking up to an hour as the bird must shiver—rapidly contracting its muscles—to generate enough internal heat to raise its body temperature. The bird is sluggish and vulnerable during this entire warming period, which is why torpor is a last resort, but a necessary one to prevent starvation.
Late-Day Activity and Migration
Confusion about nocturnal activity often arises from the intense feeding seen just before darkness sets in. Hummingbirds enter a state of hyperphagia, or increased feeding, in the late afternoon to build up the necessary fat reserves for the night’s torpor. They will aggressively visit feeders and flowers until the light is almost entirely gone, ensuring their energy tank is full before roosting.
On occasion, artificial lights near homes can confuse a hummingbird, causing it to briefly forage or flit around late into the evening, but this is not sustained flight or regular nocturnal behavior. While most hummingbirds are strictly diurnal migrants, some species, such as the Ruby-throated Hummingbird, undertake sustained, low-altitude flights overnight. This exception occurs when they are forced to cross large ecological barriers, like the Gulf of Mexico, where they cannot land or refuel until the other side.