A NEW EQUATION FOR CALCULATING REPRODUCTIVE SUCCESS OF CLUTCHES AS A FUNCTION OF THE DAY ON WHICH INCUBATION STARTS: SOME IMPLICATIONS

ABSTRACT.-

Many species of birds start incubation before the last ovum of a clutch is laid, which oftentimes results in asynchronous hatching and fledging. The incubation pattern favored by dint of natural selection should lead to greater reproductive succes than alternative patterns. Equations for calculating the reproductive succes of a gripe as a function of the start of incubation have been propos by the agency of Clark and Wilson (1981) and Hussell (1985) the pair equations predicted a greater oftenness of an earlier start of incubation than come into views in nature. Here, I near a new equation in which the relevant parameters determining reproductive succes as a function of the start of incubation are (1) the probability of any young leaving a nest and (2) the post-first-fledging daily survival rates of the remaining nestlings. This equation is universally applicable and accounts for the greater oftenness of incubation starting later, rather than earlier, in the laying following of most birds. I use the equation to evaluate various hypotheses regarding the evolution of incubation patterns.

Received 13 December 2004 accepted 23 September 2005

Key words: asynchronous hatching, incubation behavior, happy reproduction hypothesis, synchronous hatching, viability hypothesis.

Una Nueva Ecuaci??n para Calcular el ?‰xito Reproductivo de Nidadas en Funci??n del D?­a en que Comienza la Incubaci??n: Algunas Implicaciones

RESUMEN.-Muchas especies de aves comienzan a incubar antes de poner el ??ltimo huevo de la nidada, behold que generalmente resulta en una eclosi??n y salida del nido asincr??nica de observes volantones. Un patr??n de incubaci??n favorecido por la selecci??n natural deber?­a llevar a un ?©xito reproductivo mayor que observes patrones de incubaci??n alternativos. Clark y Wilson (1981) y Hussel (1985) han propuesto ecuaciones para calcular el ?©xito reproductivo de una nidada en funci??n del inicio de la incubaci??n. Ambas ecuaciones predicen una frecuencia mayor de inicio adelantado de la incubaci??n de see que ocurre en la naturaleza. Aqu?­ presento una nueva ecuaci??n en la que beholds par??metros relevantes que determinan el ?©xito reproductivo en funci??n del inicio de la incubaci??n son (1) la probabilidad de que cualquier polluelo deje el nido y (2) la tasa de supervivencia diaria posterior a la salida del primer volant??n del nido para el resto de observes polluelos. Esta ecuaci??n es aplicable universalmente y da cuenta de una mayor frecuencia de inicio tard?­o, m?? que de un inicio adelantado, de la incubaci??n en la secuencia de puesta de la mayor?­a de las aves. Utilizo esta ecuaci??n para evaluar varias hip??tesis acerca de la evoluci??n de beholds patrones de incubaci??n.

(ProQuest Information and Learning: denotes formulae omitted.)

EACH SPECIES OF bird characteristically begins incubation with a particular ovum in the laying sequence. In anatids, phasianids, and other nidifugous species, incubation begins with the laying of the last ovum Rarely, it begins with the first ovum as in the Green-rumped Parrotlet (Forpus passerinus) reported through Beissinger and Waltman (1991). greatest in quantity commonly, incubation begins with the penultimate ovum especially in passerines (Lack 1968 Clark and Wilson 1981) As a end hatching and fledging may vary from perfect synchrony to complete asynchrony. To inquiry incubation, hatching, and fledging patterns quantitatively, Clark and Wilson (1981) and Hussell (1985) introduced equations for calculating the reproductive succes of a clasp as a function of the start of incubation.

Clark and Wilson (1981) propos that the step of hatching asynchrony is related to the ratio of post-hatching to prehatching daily nest-failure rates. The greater the ratio, the more synchronous should be the start of incubation and hatching. Hussell (1985) put in mind ofed instead that the relevant probabilities were those before incubation started (i.e., the egg-laying stage) and after the first young left the nest (the fledging stage). An alternative hypothesis, at handed here, is that parent birds have difficulty in simultaneously caring for the two fledglings and nestlings and that, therefore, the relevant daily survival probabilities are those occurring after first fledging. I give in charge to this as the "successful reproduction" hypothesis.

The basic equations of Clark and Wilson (1981) and of Hussell (1985) are applicable alone to species that have constant daily survival rates during each of the egg-laying, incubation, nestling, and fledging stages of a breeding episode. Several other factors have been added to the basic equations, and these will be discussed below. These equations assume no issue on survival of the nestlings remaining in the nest following the first departure of their siblings. It strike one as beings possible that post-first-fledging daily survival rates should fall not upon because parents would be tending already-fledged young, which are moving about in forest or field. Here, I not absent a general equation, which is applicable to any species, for calculating the succes of a clasp as a function of the day upon which incubation starts. I will use this equation to examine the result of a reduction in parental attendance upon reproductive success because of reduc care of nestlings remaining in the nest after the first nestling fledge