<P> 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 who are only cared for by one parent in Iberian rock sparrows . (Vicente García - Navas) </P> <P> 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) </P> <P> 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 who has invested more into the reproductive effort . Robert Trivers (1972) </P> <P> Polyandry care occurs in roughly 9% of bird species (approximately 852 species). (Andrew Cockburn) The two forms of polyandry are sequential and simultaneous polyandry . Sequential polyandry refers to the mating strategy females use in certain situations . First, they will mate with one male and raise the offspring for a short period of time . Then they will mate with another male and care for that clutch resulting in more genetic diversity and quantity of the offspring per season . Females never incubate offspring alone unless the male has been killed . Some examples of birds who practice sequential polyandry include spotted sandpipers and red - necked phalaropes . Temminck's stint, little stint, mountain plover, and sanderling are very similar because the females lay a clutch of eggs and the males incubate them . A second clutch is laid that the female incubates herself . </P>

What is the relationship between parental care and survival of the young