Early scientific research had the mistletoe and mistletoebird mutually co-evolving with a high dependence on each other through their evolutionary development.

The flowerpecker genetic subdivision is based on a single morphological character_)—the length of the outermost primary wing feather.

Most flowerpeckers are sexually dichromatic, have stouter bills than sunbirds and display a broad variety of tongue structure.

[11] The specific epithet hirundinaceum derives from the name of the swallow (Hirundo) and refers to its long and pointed swallow-like wings.

[13] The mistletoebird has long pointed wings and a short square tail with a slight notch at the tip.

[16] Also, the denseness of the mistletoe bush and the characteristics of its leaves makes it a cool and safe place for birds to rest, hide, and nest.

In a recent study in southern Australia, 217 species of Australian arboreal birds were reported nesting in mistletoe, including the mistletoebird.

In becoming frugivore specialists, both these birds live off the fruit of parasites that germinate in the canopy of host trees, where the fruit of the parasite has specific seed placement requirements on host branches and resists consumption by frugivore nonspecialist birds.

[10] The mistletoe plant minimizes opportunistic consumption of their berries by less specialized dispersal birds by producing few, inconspicuous fruits over a long period.

[15] The mistletoebird has a small muscularized stomach and short alimentary canal, where the amount of mechanical grinding and chemical digestion is minimized.

This enables a clear passage and quick exit of the mistletoe fruit seeds through the mistletoebird's digestive system.

In comparison, the non-specialized fruit-eating birds that they compete with for the mistletoe berry, such as the spiny-cheeked honeyeater (Acanthagenys rufogularis), have a more complex digestive system that takes longer for the fruit seeds to pass, and in the process the seeds are subjected to more mechanical and chemical action in the gut.

Comparing the frugivore mistletoebird with a similarly sized insectivore the inland thornbill (Acanthiza inornata), where both their body masses are approximately 7 g (0.25 oz).

The texture of the defecated seed with the mistletoebird is stickier than other bird's feces to facilitate a strong bond with the host tree branch.

The nest can be found in many different plants but especially in eucalyptus, mistletoe, and acacia trees where it is suspended from an outer twig or thin horizontal branch and concealed among foliage.

Newly hatched birds are initially fed arthropods, after which mistletoe berry pulp is then gradually introduced into their diet.

After about two weeks, when they are ready to fledge, the mistletoe berry pulp comprises 80% of food intake of the young mistletoebird.

Heard in all seasons and given by both sexes, they have been recorded mimicking the mulga parrot (Psephotus varius), as well as more than 25 different species of passerines.

Avian richness increases with mistletoe density until a threshold of approximately 20 plants per hectare is reached after which heavy grazing and degradation sets in.

One farmer in Australia in the 1930s claimed to have destroyed over 1200 mistletoebirds in a six-year period, but they are no longer actively persecuted.