Family Trochilidae
hummingbirds

Hummingbirds belong to the order Apodiformes, meaning, "unfooted birds." There are three families in this order: Trochilidae (hummingbirds), Hemiprocnidae (tree swifts), and Apodidae (swifts). The family Trochilidae belongs to its own Suborder, Trochili. Although the number of genera and species in this group changes continually, currently there are 102 recognized genera and 328 species of hummingbirds. The hummingbird family is divided into two sub-families: Phaethornithinae (hermits) composed of 34 species and a larger group, Trochilinae (trochilines or "typical" hummingbirds), with 294 species.

Hummingbirds feed primarily on the nectar of flowers and supplement their diet with small insects. They have evolved unique characteristics such as narrow elongated beaks, extendable tongues and hovering flight, all of which allow them to exploit nectar resources.

Most hummingbird species are polygynous (males mate with more than one female) and are sexually dimorphic (sexes do not look alike); males (especially trochilines) often have bright iridescent feathers while females have more cryptic coloration. Some male hummingbirds have elaborate ornamentation such as elongated tail feathers and iridescent crests. Male hermits display together in large groups called leks while trochilines are mainly territorial; their courtship often involves dramatic aerial displays.

Known for their small size (the smallest species of hummingbird weighs 2 g), rapid wing movements and heartbeat, hummingbirds can compensate for their high energetic requirements by going into torpor during cold nights. This is especially important for those species found at high elevation where nighttime temperatures can dip below freezing.

Hummingbirds are found in a variety of habitats and while their range includes much of the New World, most hummingbird species are Neotropical. (Campbell and Lack, 1985; Gill, 1995; Schuchmann, 1999)

Hummingbirds are found only in the New World in the Nearctic and Neotropics. Their range extends from Alaska to Labrador in the North to Tierra del Fuego in the south and from Barbados to the Juan Fernandes islands. Most species are tropical and sub-tropical and live between 10 degrees N and 25 degrees S lattitude. More than half of all species of hummingbird are found in Brazil and Ecuador. (Campbell and Lack, 1985; Schuchmann, 1999; Tyrrell and Tyrell, 1985)

Hummingbirds feed and nest in a wide variety of terrestrial habitats, both temperate and tropical. The main habitat requirement for hummingbirds is a large number of nectar producing flowers. This requirement is satisfied in a number of different habitats: arid scrub, desert oasis, coastal lowland, tropical rainforest, Neararctic pine forests, and alpine tundra. Hummingbirds can be found in habitats from coastal areas at sea level to mountainous areas at an elevation of 5000 m.

Due to the prevalence of hummingbird feeders and cultivated gardens, hummingbirds can sometimes be found in urban and suburban areas with few natural food sources. There are also some agricultural crops, such as banana and coffee that can support hummingbirds. (Campbell and Lack, 1985; Sargent and Sargent, 2001; Schuchmann, 1999)

When classified using anatomical and morphological characteristics, hummingbirds are generally placed in the order Apodiformes along with tree swifts (Hemiprocnidae) and true swifts (Apodidae). Hummingbirds have also been grouped with nightjars (Caprimulgiformes), mousebirds (Coliiformes) and perching birds (Passeriformes). There is some debate about whether hummingbirds should be placed in their own super-order and/or order, Apodimorphae and Trochiliformes respectively, but most often they are grouped with the swifts in Apodiformes.

Characteristics shared with swifts include: long wings with a short, thick humerous, long manus, unique cup-and-ball joint attachment of the coracoid to the sternum, enlarged flight muscles, short secondaries, 10 tail feathers, 1 molt/year, unmarked eggs, and small feet with sharp, curved claws.

Distinguishing characteristics: long slender bills, nectivores, enlarged, deeply keeled sternum, eight ribs, elongated hyoid bones that allow the bifurcated tongue to be extended, 14-15 cervical vertebrae, nighttime torpor, and iridescent feathers.

Plumage characters, nest structure and nest site are usually good indicators of lower taxa. (Campbell and Lack, 1985; Gill, 1995; Grant and Grant, 1968; Howell, 2002; Johnsgard, 1997; Payne, 2003; Sibley and Ahlquist, 1990)

Hummingbirds are known for their small size, long, thin bills, and amazing agility in flight. The smallest hummingbirds, reddish hermits (Phaethornis ruber) and bee hummingbirds (Mellisuga helenae) weigh less than 2 g while giant hummingbirds (Patagona gigas) weigh 19 to 21 g. Most species weigh 2.5 to 6.5 g and are 6 to 12 cm in length. Their bills are a variety of shapes; bill length and shape are often good indicators of the types of flowers each species feeds on. Hummingbirds have extendable bifurcated tongues that are used to extract nectar from flowers.

As the name of their order, Apodiformes (“unfooted birds”) suggests, hummingbirds have characteristically small feet. They are unable to walk on the ground and will fly rather than walk in order to shift on a perch.

Hummingbirds have many skeletal and flight muscle adaptations that allow for hovering and high maneuverability in flight. They are the only birds that truly hover and are capable of both forward and backward flight. The characteristic humming sound they make in flight is caused by modified outer primary feathers and is the basis for their common name. Hummingbirds can achieve a forward speed of 45 km per hour and their wingbeat ranges from 70 to 80 beats per second in smaller birds to 10 to 15 beats per second in giant hummingbirds. Their heartbeat is equally rapid ranging from 500 to 600 beats per minute while resting to over 1000 beats per minute when active.

There are two sub-families of hummingbird, hermits (Phaethornithinae) and “typical” hummingbirds or trochilines (Trochilinae). Hermits generally have brownish, grayish and reddish colors and no iridescence. Trochilines often have iridescent feathers of metallic red, orange, green and blue. Iridescence is seen most in male hummingbirds and occurs on the head, upperparts and underparts. Some males also have elegant ornamentation such as bright throat gorgets, crests and elongated tail feathers.

Hummingbirds are sexually dimorphic. Females can be bigger than males, but males are usually more colorful and can have additional adornments. Female hummingbirds have more cryptic coloration than males, most likely so that they do not attract predators to the nest when incubating and feeding chicks. The plumage of immature birds is usually similar to that of females. (Campbell and Lack, 1985; Gill, 1995; Howell, 2002; Johnsgard, 1997; Sargent and Sargent, 2001; Schuchmann, 1999; Tyrrell and Tyrell, 1985)

Both male and female hummingbirds usually live from 6 to 12 years and have been known to survive up to 17 years in captivity. It is difficult to estimate annual survival, but for North American species it is thought to be 30 to 45 percent. (Sargent and Sargent, 2001; Schuchmann, 1999; Stokes and Stokes, 1989; Tyrrell and Tyrell, 1985)

Hummingbirds are solitary animals. They are polygynous and males provide no parental care. Males of many species of hummingbird are territorial and the territories, which are usually centered around a food source, are aggressively defended by their owners. Territorial individuals will perch in a conspicuous spot (often the top of a tree) and watch for intruders. If an intruder is spotted the territory holder will give warning calls, perform hovering displays while flashing iridescent feathers and if necessary, chase off the intruder. Occasionally agonistic interactions will escalate and the birds will attack each other, sometimes using their beaks as weapons. When food is scarce, territory owners will use less energetically expensive behaviors to exclude intruders. Females may also set up territories surrounding nest sites. Those hummingbirds that are not territorial are mainly trap-line feeders; they will move throughout an area and feed on numerous patches of flowers.

Hermits usually form leks and congregate on traditional lekking grounds, where females visit to choose a mate. Male hummingbirds are known for their spectacular display flights that they perform in front of females during courtship and in view of intruding males during agonistic interactions. During a display flight, a male hummingbird can ascend up to a height of 30 m or more, and will dive toward the female or intruding male (often coming within centimeters of the recipient of the display), chipping at the bottom of the dive before ascending again.

Because of their high metabolic rate and the cost of their active flight, hummingbirds spend on average 70% of their time perched (often preening). They are very curious and will investigate brightly colored objects as potential food sources. They are diurnal and forage throughout the day, with peak activity at dawn and dusk.

In order to save energy during cold nights, hummingbirds will go into torpor. During torpor their body temperature decreases 20 to 30 degrees, their heartbeat can go below 50 beats per minute and their breathing becomes irregular. Most bird species are too large to use torpor to save energy since it would take too long and use too much energy to warm back up. It can take hummingbirds as long as an hour to come out of torpor, and if they are disturbed they cannot immediately resume normal activity.

Most tropical hummingbird species do not migrate but some will change elevation in response to changing temperatures or seasons. North American hummingbirds migrate and may fly distances of more than 5,000 km round trip. Males are the first to arrive at breeding and wintering grounds and are followed by females and juveniles. Because of the energetic costs of flight some hummingbirds must increase their body weight by 50% before beginning migration. (Campbell and Lack, 1985; Gill, 1995; Johnsgard, 1997; Schuchmann, 1999; Skutch and Singer, 1973; Tyrrell and Tyrell, 1985)

Both male and female hummingbirds have species-specific calls. Calls are usually short, high-pitched chips but some species have more drawn-out, musical songs. Singing is used both to attract mates and deter intruders. The humming noise made by wings during flight may also be a form of communication, especially in dive displays. Nestlings in domed or semi-domed nests will make begging calls but those in open cup nests will not. Fledglings make contact calls to communicate with their mothers when they are out of sight and begging calls when they are close by. Alarm calls may also be given when predators are nearby.

Hummingbirds, like most other birds do not have a well-developed sense of smell. They have color vision and unlike most vertebrates, are sensitive to ultra-violet light between 325 to 360 nanometers. Ultra-violet perception may help the birds find food since some flowers have ultra-violet color patterns. Male coloration is a cue used by females and conspecific competitors to assess dominance, quality and species identity. (Campbell and Lack, 1985; Howell, 2002; Johnsgard, 1997; Schuchmann, 1999)

Hummingbirds are nectivores and insectivores; approximately 90% of their diet comes from nectar and 10% from arthropods (flies (Diptera), wasps (Hymenoptera), spiders (Araneae), beetles (Coleoptera), and ants (Hymenoptera)). Thin, elongated hummingbird bills are well adapted to exploit nectar sources. Hummingbird pollinated flowers are usually brightly colored, scentless and have long, tubular corollas. The shape of a hummingbird’s bill determines the species of flower it can feed on. In fact, co-evolution of flower shape and bill shape is a well-studied phenomenon. Hummingbirds have also developed specialized flight structures that allow them to hover in front of flowers while feeding. Without the ability to hover, hummingbirds would not be able to obtain nectar from flowers. In addition, hummingbirds have specialized, bifurcated tongues that they can extend to reach nectar from within a flower. They use capillary action to draw the nectar along their tongue.

Because hummingbirds have a high basal metabolic rate, they can drink their body mass in nectar in less than a day. They get some amino acids from pollen and protein from insects (which they catch by hawking or hover-gleaning). When nectar resources are scarce, hummingbirds will also feed on sap from holes in trees made by sapsuckers (Sphyrapicus).

Co-existing species of hummingbirds will specialize on certain flowers or subdivide the habitat. They will either defend nectar resources on a territory or move between patches of flower-rich areas, a behavior called traplining. (Campbell and Lack, 1985; Howell, 2002; Schuchmann, 1999; Skutch and Singer, 1973)

Adult hummingbirds have few predators. Known predators include snakes (Serpentes), forest falcons (Micrastur, that catch hermits during lekking), and pygmy-owls (Glaucidium). Nest predators are the biggest threat to hummingbirds. These include jays (Corvidae), toucans (Ramphastidae), and some bats (Micro-chiroptera).

Female hummingbirds have more cryptic coloration than male hummingbirds. This is thought to be an adaptation that allows the females to be more camouflaged and avoid attracting predators when incubating. Females will fly to their nests in zigzags or semi-circles to avoid leading a predator directly to the nest. Hummingbirds have also been seen mobbing predators. (Campbell and Lack, 1985; Skutch and Singer, 1973)

Many species of plants rely on hummingbirds for pollination. For some species, hummingbirds are their sole pollinators. In Brazil alone, hummingbirds pollinate 58 different plant species.

Hummingbirds often pick up nectar mites (Acari) when they visit flowers. The mites climb onto the hummingbird’s bill and into the nostrils. Here they are transported from flower to flower. The mites do not harm the birds; they reproduce on the plants and eat pollen and nectar. At least forty species of mites have been described. (Campbell and Lack, 1985; Grant and Grant, 1968; Howell, 2002; Stokes and Stokes, 1989)

There are no known adverse affects of hummingbirds on humans.

In the past, hummingbirds were actively hunted for feathers that were used to make jewelry and adorn clothing. They were also captured for human amusement in zoos and private collections. Hummingbirds are still sold in markets as aphrodisiacs; although there is no scientific evidence that they work.

Beyond the ecosystem services hummingbirds provide (pollination of a wide variety of plant species), perhaps their biggest economic influence can be seen in the market for hummingbird feeders and eco-tourism. (Schuchmann, 1999; Tyrrell and Tyrell, 1985)

Two species of hummingbird are known to be extinct: Brace’s emerald (Chlorostilbon bracei) and Gould’s emerald (Chlorostilbon elegans). There are 9 species listed as critically endangered by the IUCN, 11 listed as endangered and 9 listed as vulnerable. Major threats to hummingbirds are habitat loss, degradation, and fragmentation. Most of the North American species are protected under the Migratory Bird Treaty Act. No hummingbirds are listed by ESA, but almost all, if not all are listed by CITES.

Habitat destruction in the tropics does not threaten hummingbirds as much as it does some other Neotropical species. Hummingbirds can usually find nesting habitat even in human modified landscapes; cleared areas may still produce flowering plants and some plantations (banana and coffee) can support hummingbirds. Feeders and garden flowers have also allowed population and range increases in some North American species. ("UNEP-WCMC Species Database: CITES-Listed Species", 2003; IUCN, 2002; Sargent and Sargent, 2001; Schuchmann, 1999; Threatened and Endangered Species System, 2003; U.S. Fish and Wildlife Service, date unknown)