page_title: House sparrow
section_title: Physiology
hierarchical_section_title: House sparrow / Physiology
caption_attribution_description: Passer domesticus, Alpenquai in Zürich (Switzerland)
context_page_description: The house sparrow is a bird of the sparrow family Passeridae, found in most parts of the world. It is a small bird that has a typical length of 16 cm and a mass of 24–39.5 g. Females and young birds are coloured pale brown and grey, and males have brighter black, white, and brown markings. One of about 25 species in the genus Passer, the house sparrow is native to most of Europe, the Mediterranean Basin, and a large part of Asia. Its intentional or accidental introductions to many regions, including parts of Australasia, Africa, and the Americas, make it the most widely distributed wild bird.
  The house sparrow is strongly associated with human habitation, and can live in urban or rural settings. Though found in widely varied habitats and climates, it typically avoids extensive woodlands, grasslands, and deserts away from human development. It feeds mostly on the seeds of grains and weeds, but it is an opportunistic eater and commonly eats insects and many other foods. Its predators include domestic cats, hawks, owls, and many other predatory birds and mammals.
  Because of its numbers, ubiquity, and association with human settlements, the house sparrow is culturally prominent.
context_section_description: House sparrows express strong circadian rhythms of activity in the laboratory. They were among the first bird species to be seriously studied in terms of their circadian activity and photoperiodism, in part because of their availability and adaptability in captivity, but also because they can "find their way" and remain rhythmic in constant darkness. Such studies have found that the pineal gland is a central part of the house sparrow's circadian system: removal of the pineal eliminates the circadian rhythm of activity, and transplant of the pineal into another individual confers to this individual the rhythm phase of the donor bird. The suprachiasmatic nuclei of the hypothalamus have also been shown to be an important component of the circadian system of house sparrows. The photoreceptors involved in the synchronisation of the circadian clock to the external light-dark cycle are located in the brain and can be stimulated by light reaching them directly though the skull, as revealed by experiments in which blind sparrows, which normally can still synchronise to the light-dark cycle, failed to do so once India ink was injected as a screen under the skin on top of their skulls.
  Similarly, even when blind, house sparrows continue to be photoperiodic, i.e. show reproductive development when the days are long, but not when the days are short. This response is stronger when the feathers on top of the head are plucked, and is eliminated when India ink is injected under the skin at the top of the head, showing that the photoreceptors involved in the photoperiodic response to day length are located inside the brain.
  House sparrows have also been used in studies of nonphotic entrainment (i.e. synchronisation to an external cycle other than light and dark): for example, in constant darkness, a situation in which the birds would normally reveal their endogenous, non-24-hour, "free-running" rhythms of activity, they instead show 24-hour periodicity if they are exposed to two hours of chirp playbacks every 24 hours, matching their daily activity onsets with the daily playback onsets. House sparrows in constant dim light can also be entrained to a daily cycle based on the presence of food. Finally, house sparrows in constant darkness could be entrained to a cycle of high and low temperature, but only if the difference in temperature was large (38 °C versus 6 °C); some of the tested sparrows matched their activity to the warm phase, and others to the cold phase.
caption: An immature house sparrow sleeping
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