Today we'd like to share with you the meaning of the term altricial, especially as it relates to birds. It is the opposite of a term we shared earlier on the blog: precocial. Let's learn about what it means to be altricial!
The term altricial comes from the Latin alere, which means "to nurse, to rear, or to nourish." An altricial species is one in which the newly hatched or born young need to be cared for by their parents for an amount of time. While a precocial animal may be mobile and relatively independent within days or even hours of being born or hatched, an altricial species must rely on its parents to survive for a period of weeks, months, or even years before it is independent.
In birds, this means youngsters come out of the egg almost completely naked. They are relatively immobile, needing to stay in their nest, and some have closed eyes as well.
While having helpless babies may seem to be a disadvantage, there are advantages to this breeding strategy. Altrical eggs are smaller, relatively speaking, than precocial eggs, resulting in less biological stress to mother birds. Precocial animals are born or hatched with brains relatively large compared to their body size, but don't grow much as they mature. Altricial species are born or hatched with smaller brains which grow as the animal matures. In general, altricial species therefore "have a wider skill set" when they reach full maturity.
Most songbirds have altricial young, as do owls, hawks, herons, and woodpeckers. Rodents, cats, dogs, and humans also have altricial young, which rely on their parents for the first few weeks or decades of life, depending on the species and individual young.
When most people think of owls, one of the facts that often comes up is that they are nocturnal. Nocturnal animals are most active during the night, sleeping by day. While most owl species are nocturnal, not all are. Adaptations found in nocturnal animals include enhanced eyesight, hearing, and sense of smell. Besides owls, other bird species known for being nocturnal include the Southern Brown Kiwi, the Kakapo, and the Common Nighthawk. Familiar nocturnal animals include bats, raccoons, and fireflies.
Diurnal animals are most active during the day, and sleep at night. For the most part, all animals first evolved to be diurnal. Nocturnal animals later evolved adaptations for being active at night in order to avoid predators and reduce competition with other species. Advanced color vision is an adaptation seen in diurnal animals. While most birds are diurnal, many species migrate at night, mostly to avoid predation. Animals known for being diurnal include most reptiles, pollinator insect species, and primates (including humans).
There are other terms to describe when animals are active:
Crepuscular animals are most active during twilight hours, around dawn and around dusk. Examples of crepuscular birds include the Barred Owl and Chimney Swift.
Cathemeral animals are active during spurts of time during the day and night. The activity is sporadic and occurs at irregular intervals. Cathermal animals are usually active during parts of both daytime and nighttime. Lions and some species of lemur are known for being cathermal.
Oology is the study of bird eggs. It also refers to the study of bird nests and breeding behavior. Oology can also refer to the hobby of egg collecting, which is illegal in many locations.
Early scientific ornithological study often involved collecting birds by shooting them to study their anatomy and plumage up close. It also involved the collection and study of their eggs. Scientists studying the difference between samples of Pergrine Falcon eggs over time were able to identify DDT usage as the cause of a decline in raptor populations in the 1960s and 1970s.
Egg collecting as a hobby remained popular as the scientific value of this type of study declined. This was extremely popular especially in the United Kingdom, though the hobby was denounced by the British Ornithologists' Union as early as 1922. Although UK laws have made the amateur hobby collection of eggs illegal since 1954, oologists continue to pursue the hobby by collecting eggs. Egg collecting is illegal in many other jurisdictions as well, including the United States.
Allopreening refers to one animal preening another. While preening and grooming are usually individual actions, in some species, birds or animals will preen one another. This occurs in birds as well as other classes of animal.
We previously mentioned allopreening when discussing vultures during Vulture Week in 2015. The post Glossary of Vulture Terms explained, in part, that "allopreening refers to social grooming between multiple individuals, often performed to strengthen social bonds."
Social bonds may not be the only reason that birds preen or groom one another. Allopreening is most common in species that tend to gather in large flocks. In these species, birds in frequent close proximity to each other are more likely to transfer parasites amongst the close-knit group. Allopreening in these species helps to keep pests like ticks under control.
Allopreening between mated pairs of birds occurs more often in species where both the male and female raise their offspring together. The preening ritual may help strengthen the longer-lasting bond. In mated pairs where the birds may be separated for a long period of time, allopreening is part of a greeting ritual. For example, this type of allopreening occurs when male and female penguins are reunited after a long incubation shift where one of the mates was feeding at sea for days or weeks.
Allopreening may also help to reduce conflict or tensions among large flocks or breeding colonies of birds. The social structure of the colony plays a large part in who receives preening and how much.
Some birds have fleshy growths hanging or protruding from the head or the neck. When these are a normal part of their anatomy, they are called caruncles.
Caruncles are often made of bare skin, though some may have a sparse covering of small feathers. They are usually bright in color, like the bright red comb of a domestic chicken.
Caruncles are thought to be ornamental in nature, found in male birds and used to attract mates, though caruncles are found in females of some species, too. Large bare patches of flapping skin may also be used to thermoregulate the bird, especially in warm climates.
Some caruncles have specific names depending on where they are found on the body.
Comb A comb or cockscomb is a caruncle that grows on the top of the head. Males and females of a species may both have a comb, but it is generally larger in male birds. Combs are found in domestic chickens, like the Faverolles, and related bird species.
Wattle A wattle is a caruncle that hangs from the head or the neck. Wattles come in a set of two; when one such growth is present, it is known as a dewlap. On the Wattled Crane, the wattles hang from the upper throat and are almost fully feathered. Another wattled bird named for this distinguishing feature is the Long-wattled Umbrellabird.
Snood A snood is a caruncle that hangs from the forehead, and can extend over the beak. These are found in both the Wild Turkey and domestic varieties. During courtship, the snood elongates and darkens in male birds.
The King Vulture has an unusual caruncle on its beak, which appears as an orange fleshy crest-like protuberance attached to the cere.
A brood patch is a bare area of skin that some birds develop during nesting. The bare skin is an adaptation to help with egg incuabation.
The patch of featherless skin allows the parent bird to provide extra warmth from his or her own body to the eggs in the nest, and to growing, naked, newly-hatched chicks in the first days of life.
Both males and females can develop a brood patch, depending on the species and how incubation duty is shared. In most species, the brood patch develops as feathers are naturally shed during nesting activities. In some species, the brood patch appears through self-plucking. Ducks and geese, for instance, may line their nest with soft breast feathers, exposing the skin.
The location of the brood patch on the adult bird's body depends on the species. Most birds have a single bare patch of skin, while some species may develop two or even three patches.
Fun Fact: Bird banders use the presence of a brood patch to determine if a bird is currently nesting. The presence of a brood patch can also help to sex or age the bird. The patch on most birds is not immediately visible on the bird's body; banders gently blow air on the belly to separate the surrounding feathers to see if a patch is present.