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.

Some other species with caruncles include the Masked Lapwing (wattles), Andean Condor (comb and wattles), and the White-winged Guan (dewlap). Can you think of other bird species that have caruncles?

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.

We're celebrating cranes on the Birdorable blog this week! Today we'd like to share a bird term that relates to cranes and other birds. Let's learn about what it means to be precocial!

The term precocial comes from the Latin praecocia, which refers to "places where fruits ripen early." A precocial species is one in which the newly hatched or born young are relatively mature. In birds, this means the baby is usually covered in downy feathers and is able to walk and even feed itself within a short time of hatching. This adaptation is found in most ground-nesting birds as a strategy to evade predators when the nest offers little shelter.

Cranes have precocial young, as do many other birds, including ducks and geese, chickens, and rails. Malleefowl chicks can even already fly within a day of hatching. There are some mammals born precocial, like the Hartebeest, whose calves can stand and walk within hours of being born.

On the other end of the development spectrum are altricial babies. In birds, this usually means at the time of hatching the chick is naked (without feathers), has its eyes shut, and is completely helpless and dependent on its parents for care all of its needs.

Two other terms related to precocial and altricial are nidifugous and nidicolous. Nidifugous species leave the nest site shortly after hatching; all nidifugous species are precocial but not all precocial species are nidifugous. Precocial birds that remain in the nest for a period are called nidicolous.

We're celebrating gulls on the blog this week! Today we'd like to share a bird term that relates to some species of gulls. Let's find out about kleptoparasitism!

Kleptoparasitism is just what it sounds like - parasitism by theft (klepto-). It basically refers to one animal stealing food from another. Before we go on, it should be made clear that gulls are not the only species that engage in this behavior. They aren't even the only birds that do so.

Why would one animal steal food from another? In some cases, the thief takes prey items that it would not be able to capture on its own. Sometimes the kleptoparasite steals food opportunistically, or to save the time and effort of obtaining prey. Kleptoparasitism can also refer to the theft of non-food items, like when Chinstrap Penguins steal nest material from other penguins to use in their own nest.

Birds in the seabird family Skua are known for their kleptoparasitic behavior. Some species of skua obtain a significant percentage of their food using this method, stealing prey caught by other seabirds.

Frigatebirds are known for this behavior as well, giving them the appropriate nickname "pirate of the sea".

Gulls can be both perpetrators and victims of kleptoparasitism. Heermann's Gulls and Laughing Gulls are known to steal fish from Brown Pelicans, snatching anything that escapes from the pelican's bill as it surfaces from a hunt. Gulls may chase others of their own species in order to steal freshly caught prey or found food items.

Chasing down deep diving fish hunters is a way for non-diving gulls to obtain food not otherwise available.

Gulls have also been known to steal food from humans! Has this ever happened to you?

The crop is a fascinating aspect of avian anatomy, serving as a crucial part of the digestive system in many bird species. This expandable pouch, typically found at the throat, acts as a storage space for food prior to digestion. While most commonly associated with birds, the crop is also present in certain species of snails and earthworms and was a feature in some dinosaurs species.

In the avian world, the crop's visibility can often be noted externally, particularly when it is filled with food. However, it's important to note that not all bird species possess a crop. For example, pigeons and doves not only use their crop to store food but also to produce a nutritious substance called crop milk, which is essential for feeding their young.

Scavenging birds such as vultures and condors often gorge themselves when food is available, filling their crop to its maximum capacity. This allows them to store excess food for later digestion, a vital adaptation in environments where food availability is unpredictable. The crop enables these birds to feed efficiently and sustain themselves over longer periods.

Interestingly, while many raptor species like hawks, eagles, and ospreys have a crop, owls are an exception in this regard. Another notable use of the crop is in birds that regurgitate food for their young. In these species, the crop plays a role in softening the food before it is fed to the chicks, ensuring that the young birds receive nourishment that is both digestible and nutritious.

The crop's function in avian digestion and parental care highlights the intricate adaptations birds have evolved to thrive in various environments and life stages.

A lot of bird species are migratory. That means that they spend part of the year in one place and then travel (fly) to another place for some time. Migration is typically based around ideal conditions for breeding versus availability of food depending on location and season.

By the way, migration isn't limited to birds. In fact, some species in all major animal groups experience migration. Some well-known examples include the great wildebeest migration in Africa, the multi-generational migration of Monarch butterflies, and salmon runs from the Pacific and Atlantic Oceans into freshwater rivers.

Birds that breed across North America and migrate south to New World neotropics for the winter are known as Neotropical Migrants. Some definitions of the term use the latitude of the Tropic of Cancer (23 degrees north) as a benchmark: birds that breed above this line and winter below it are considered to be Neotropical Migrants.

The over 200 species of Neotropical Migrant birds come from different families, though a majority of species are songbirds. Shorebirds, birds of prey, and waterfowl may also be Neotropical Migrants.

Among these long-distance migrants are Red Knots, with a breeding range that extends into northern Canada and a winter range as far south as the southernmost point of South America. A Red Knot could travel up to 10,000 miles per one-way trip!

Bobolinks are also Neotropical Migrants; individual birds may travel over 6,500 miles one way, from northern Canada down to Argentina.

Neotropical Migrant birds face a variety of threats to their populations. For these birds, ample suitable habitat is required on their breeding grounds, winter sites, and all of the places that they stop along their long journeys.

Brood parasites are birds that rely on other birds, often of a different species, to raise their young. Brood parasitism occurs in organisms other than birds, including fish and insects, but we'll focus on a few well-known bird examples here.

This type of breeding strategy allows biological parents to avoid the stress and time involved in raising young.

Brown-headed Cowbird chick in Wood Thrush nest by Kelly Colgan Azar (CC BY-ND 2.0)

The strategy often involves laying eggs in several different nests in order to maximize the chances of young being raised successfully to fledge. The parasite bird also often removes an egg from the host parent to reduce discovery and improve their own offspring's chances of survival. Brood parasite birds generally have a shorter incubation period (with incubation actually starting internally within the biological mother bird) which also gives their offspring a head start over its adopted nest mates.

Common Cuckoo chick in host nest by Per Harald Olsen (CC BY 2.0)

A big risk with this strategy is discovery of intruder eggs. Some host species have learned to recognize intruder eggs in their nest, which may lead to total abandonment of the nest. Sometimes the discovery is made after hatching, and the parasitic chick is expelled from the nest. Another risk is using a host with a diet unsuitable for the growing chick. American Goldfinches are vegetarian; Brown-headed Cowbirds have an omnivorous diet and will not survive to fledge from finch parents.

Cowbirds and cuckoos are probably the most well-known species of brood parasites in the bird world.

The Brown-headed Cowbird is widespread across North America. This species has at least 221 known host species, from hummingbirds to birds of prey.

Common Yellowthroat feeding Brown-headed Cowbird by Bill Thompson (CC BY 2.0)

The Common Cuckoo of the Old World has wide distribution across Europe, Asia, and Africa. It takes a female cuckoo just 10 seconds to remove one egg and lay her own in a host's nest. Common Cuckoos have been recorded using over 100 host species. They are generally much larger than their hosts and the quickly-growing chick typically will remove all of the other eggs from the nest itself.

Brown Thornbill feeding Common Cuckoo chick by Wayne Butterworth (CC BY 2.0)

Have you ever seen a Brown-headed Cowbird, Common Cuckoo, or other brood parasite being fed by a host parent?

Sexual dimorphism refers to observable differences between males and females of the same species. In basic terms, it means that a male of a species is easily distinguished from a female. In birds this usually means differences in size or in plumage. It can also be noted in behavior differences and other traits.

Earlier on this blog we talked about the extreme sexual dimorphism in Eclectus Parrots, where males and females show extreme differences in their plumage: males are bright green while females are shades of red and blue.

Sexual dimorphism exists in most species of raptor. In birds of prey, males are often smaller than the females of the species. However, this is often difficult to discern in wild birds, especially if seen at a distance or when only one bird is present.

Many common birds also exhibit sexual dimorphism. Male ducks are often colorful, while females tend to be drab. You can see this in the common Mallard.

Mallard ducks by Connor Mah (CC BY-SA 2.0)

In songbirds, males may be brightly colored while females have a similar plumage with more muted tones, as seen in Baltimore Orioles, American Robins, Eastern Towhees, and Black-throated Blue Warblers.

Eastern Towhees: female (left) by Brian Henderson (CC BY-NC 2.0), male (right) by Dendroica cerulea (CC BY-NC-SA 2.0)

In other birds, like the Eclectus Parrot mentioned above, the plumage differences are extreme. Examples of this can also be seen in the Superb Fairywren of Australia, and the Sage Grouse.

Can you think of other bird species where the male is easily told apart from the female? Do you have birds like this where you live? What about birds that aren't sexually dimorphic? Can you think of species where male and females are impossible to tell apart by looking at them?