Disentangling the effects of date, individual, and territory quality on the seasonal decline in fitness

Abstract

The seasonal timing of reproduction is a major fitness factor in many organisms. Commonly, individual fitness declines with time in the breeding season. We investigated three suggested but rarely tested hypotheses for this seasonal fitness decline: (1) time per se (date hypothesis), (2) late breeders are of lower quality than early ones (individual quality hypothesis), and (3) late breeders are breeding at poorer territories than early breeders (territory quality hypothesis). We used Bayesian variance component analyses to examine reproductive output (breeding success, number fledged, and number of recruits) from repeated observations of female Northern Wheatears (Oenanthe oenanthe) and individual territories from a 20-yr population study. The major part of the observed seasonal decline in reproductive output seemed to be driven by date-related effects, whereas female age and territory type (i.e., known indicators of temporary quality) contributed to a smaller degree. Other, persistent effects linked to individual and territory identity did not show any clear patterns on the seasonal decline in reproductive output. To better disentangle the quality effects (persistent and temporary) of individual and territory from effects caused by the deterioration of the environment we suggest a protocol combining experimental manipulation of breeding time with a variance-covariance partitioning method used here.

Causes of seasonal decline in reproduction of the cooperatively‐breeding acorn woodpecker

“…Thus far, no long‐term trends have been detected at our study site, despite considerable annual variation, particularly in the acorn crop and its subsequent effects on reproduction. Interestingly, we have observed no relationship between the timing of budburst of valley oaks Quercus lobata , a key species for acorn woodpeckers in the study site, and mean last egg date of the population (data from 2003 to ; r = –0.09, df = 13, p = 0.75). Moreover, , an unusually warm, dry year in which budburst of the deciduous oaks was strikingly early (M. Pesendorfer and W. Koenig, unpubl.…”

“…Timing of reproduction in several nidicolous bird species has been shown to be related to food supply, with peak fledging occurring when relevant food sources are at their maximum (Lack , Klomp ) and seasonal declines in offspring quality and survival being mediated by food (Harriman et al ). Critical food for acorn woodpeckers consists of stored acorns and flying insects, both of which are consumed during the breeding season (Koenig and Mumme 1987).…”

Factors influencing plasticity in the arrival‐breeding interval in a migratory species reacting to climate change

“…Thus, we ask the following questions: (a) How are recent changes in the patterns of breeding time in the northern wheatear (Arlt & Pärt, ) reflected in changes in its arrival times and the arrival‐breeding interval; (b) What factors are related to the probability of beginning egg laying after arrival (e.g., we expect female age, the timing of arrival and the degree of spring progression to influence the arrival‐breeding interval); and (c) How does the relative importance of these factors change throughout the breeding season? Like many seasonally breeding organisms the wheatear displays a seasonal decline in fitness related to breeding time (Öberg, Pärt, Arlt, Laugen, & Low, ; Pärt, Knape, Low, Öberg, & Arlt, ); thus, we would expect factors determining the length of the arrival‐breeding interval to vary in their importance depending on the timing of arrival.…”

“…We examine these factors not only to gain insights into recent phenological changes in this species, but also to gain a general understanding of the factors that influence or constrain the timing of breeding in migratory birds. Thus, we ask the breeding organisms the wheatear displays a seasonal decline in fitness related to breeding time (Öberg, Pärt, Arlt, Laugen, & Low, 2014;Pärt, Knape, Low, Öberg, & Arlt, 2017); thus, we would expect factors determining the length of the arrival-breeding interval to vary in their importance depending on the timing of arrival.…”

Nest Site Selection Influences Cinnamon Teal Nest Survival in Colorado

“…High quality nest sites provide the proper conditions for incubation, hide eggs from predators, and provide easy access to foraging sites, thus improving reproductive success. An understanding of the relationship between breeding habitat selection and future fitness therefore has the potential to elucidate the mechanisms influencing population dynamics and to inform breeding habitat management decisions (Gunnarsson et al , Arlt and Pärt , Sedinger and Alisauskas , Gibson et al , Pärt et al ).…”