Parental care in birds

Parental care refers to the level of investment provided by the mother and the father to ensure development and survival of their offspring. In most birds, parents invest profoundly in their offspring as a mutual effort, making a majority of them socially monogamous for the duration of the breeding season. This happens regardless of whether there is a paternal uncertainty.

Origin Birds originated from earlier theropod dinosaurs and underwent body miniaturization over a 50 million year period. Changes in anatomy are rearrangement of body mass, adults retain juvenile traits including large brain mass and eyes despite a smaller snout (paedomorphism), and aerial abilities. (Michael S. Y. Lee, Andrea Cau, Darren Naish, and Gareth J. Dyke) The Archaeopteryx was the first fossil bird recorded with evolved feathers. The forelimb in the Archaeopteryx could have been used for parental care of offspring because enlarged feathers were possibly used to shield offspring from the suns' rays and for flight. (Carey, J.R., and Adams. J (2001)) Older potential avialans have since been identified, including Anchiornis, Xiaotingia, and Aurornis. Kavanau (1987) was the first to find that unique bi-parental care seen in modern birds probably evolved from extinct birds. They developed the ability to provide protection, escorting, nurturing and egg guarding abilities for their young. Evolution of homeothermy and flight most likely occurred in bi-parental birds with precocial chicks. Kavanau said extant birds (David J. Varricchio) evolved and learned flight through evolution to access ground nests faster. (Kavanau) Van Rhijn (1984, 1990), Handford and Mares (1985), and Elzanowski (1985) were the first to announce the earliest form of parental care as being mono-parental male care. Wesolowsi (1994) contradicted Kavanau's reasoning by saying flight evolved due to parental care not reproduction as previously thought. While flight was being enhanced in evolutionary stages, lack of parental care meant that the increasing number of large eggs required a higher level of investment. This created young that were able to take flight shortly after hatching which is known as precocial, in the form of unassisted paternal (male only) care. The next stage of evolution replaced this with bi-parental care (with a few exceptions). Ligon (1999) suggested with Vehrencamp (2000) that male incubation existed first and later gave way to shared and finally female only incubation. A possible evolutionary timeline by Kavanau suggests that basal theropod dinosaurs evolved into birds that evolved unique bi-parental care, after which avian birds evolved homeothermy and flight. Burley and Johnson (2002), Tullberg et al. (2002), Prum (2002), and Varricchio et al. (1999) questioned the male evolutionary shift from no care to male care. They proposed like Kavanau's model that parental care came first leading to bi-parental care in extant birds. The origin of parental care in birds is still a controversial topic today. (Tomasz Wesolowski)

Different modes of parental care

Bi-parental care Bi-parental care is the most common form in birds, especially in passerines. A mating pair equally contributes to feeding and guarding the offspring. It occurs in approximately 85% of bird species. The hatchling benefits from the mutual care at the cost of the parents' future reproductive success. Each parent tries to find a mate who will not desert the nest and has high qualities that showcase their parental skills (e.g. ornamental cues). The good parent hypothesis states that birds can invest more energy towards their own survival rate by choosing an ideal mate.

Evolution in potential mates to advertise their parental strengths through ornamental cues (e.g. a yellow chest patch in Iberian rock sparrows) are based on the differential allocation hypothesis. This hypothesis states that the bigger the ornamental cue a mate has, the more investment is put towards the offspring. As a result of bi-parental care, the offspring are usually stronger than birds which are only cared for by one parent in Iberian rock sparrows. (Vicente García-Navas)

Maternal vs paternal care In bi-parental care, the male provides food and the female is a caretaker. Both ensure the survival of the offspring. The female may care for her young by covering them to keep them warm, shielding them from the sun or from rain and guarding them from predation. The male may also feed the female, who in turn regurgitates the food to the chicks. In female red-eyed vireos the roles are reversed. Nonbreeding adults or juveniles in acorn woodpeckers contribute the care through collaboration with the parents. (Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye)

Mono-parental care Male only care occurs in only 1% of bird species (approximately 90 species). Female only care occurs in 8% of species (approximately 772 species). (Andrew Cockburn) A hypothesis states that the parent that invests less reproductive effort in comparison to its mate, will have a higher chance of deserting because it loses less if successful offspring are not produced. However, in some birds (such as the snail kite found in South America, the Caribbean and Florida), the male and the female sometimes compete over which one will desert the nest regardless of which one has invested more into the reproductive effort. (Robert Trivers (1972))

Parental care in polyandrous species

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