نتایج جستجو برای: clutch

تعداد نتایج: 2466  

Journal: :Proceedings of the National Academy of Sciences of the United States of America 2002
David W Winkler Peter O Dunn Charles E McCulloch

Across North America, tree swallows have advanced their mean date of clutch initiation (lay date) by approximately 9 days over the past 30 years, apparently in response to climate change. In a sample of 2,881 nest records collected by the lay public from 1959 to 1991, we examined whether clutch size has also responded to climate change. We found that clutch size is strongly related to lay date,...

2013
Andreas Myklebust

A dry clutch model with thermal dynamics is added to a driveline model of a heavyduty truck equipped with an automated manual transmission. The model captures driveline oscillations and can be used to simulate how different clutch-control strategies affect vehicle performance, drivability and comfort. Parameters are estimated to fit a heavy-duty truck and the complete model is validated with re...

2014
Qifang Liu Bingzhao Gao Yuan Gao

The shift control, especially clutch slip control in inertia phase, is considered as a key issue of dual clutch transmission for improving driving comfort. For the shift is a complex nonlinear dynamic process combining engine states and road information, and these are often variable, so the clutch control system can be described as a nonlinear parameter-varying model. Moreover, a novel nonlinea...

Journal: :Science 2008
David J Varricchio Jason R Moore Gregory M Erickson Mark A Norell Frankie D Jackson John J Borkowski

The repeated discovery of adult dinosaurs in close association with egg clutches leads to speculation over the type and extent of care exhibited by these extinct animals for their eggs and young. To assess parental care in Cretaceous troodontid and oviraptorid dinosaurs, we examined clutch volume and the bone histology of brooding adults. In comparison to four archosaur care regressions, the re...

Journal: :General and comparative endocrinology 2014
Calen P Ryan Alistair Dawson Peter J Sharp Simone L Meddle Tony D Williams

Clutch size is a fundamental predictor of avian fitness, widely-studied from evolutionary and ecological perspectives, but surprisingly little is known about the physiological mechanisms regulating clutch size variation. The only formal mechanistic hypothesis for avian clutch-size determination predicts an anti-gonadal effect of circulating prolactin (PRL) via the inhibition of luteinizing horm...

Journal: :General and comparative endocrinology 2015
Calen P Ryan Alistair Dawson Peter J Sharp Tony D Williams

Clutch size is a key avian fitness and life history trait. A physiological model for clutch size determination (CSD), involving an anti-gonadal effect of prolactin (PRL) via suppression of luteinizing hormone (LH), was proposed over 20 years ago, but has received scant experimental attention since. The few studies looking at a PRL-based mechanistic hypothesis for CSD have been equivocal, but re...

Journal: :The American naturalist 2006
Karen L Wiebe Walter D Koenig Kathy Martin

There are two major competing hypotheses for variation in clutch size among cavity-nesting species. The nest site limitation hypothesis postulates that nesting opportunities are more limited for weak excavators, which consequently invest more in each breeding attempt by laying larger clutches. Alternatively, clutch size may be determined by diet; the clutch sizes of strong excavators may be sma...

Journal: :Poultry science 2003
C F Chen M Tixier-Boichard

Two dwarf brown-egg layer lines, differing in their genotype for the naked neck gene (NA), line L2 (NA*NA/*NA) and line L1 (NA*N/*N), have been selected for 16 generations for increased average clutch length. A control line from the same base population, dwarf and segregating for the NA gene, was maintained by random mating. Genetic parameters were estimated by a multivariate derivative-free re...

Journal: :General and comparative endocrinology 2002
Julian K Christians Tony D Williams

It has been suggested that follicle-stimulating hormone (FSH) may play a role in egg size/number trade-offs in oviparous vertebrates. We tested this hypothesis in an avian species by administering porcine FSH (pFSH) to intact, captive female zebra finches (Taeniopygia guttata) during egg formation. We predicted that (1) pFSH would increase the number of ovarian follicles recruited into rapid yo...

2001
LIESBETH DE NEVE JUAN JOSEu SOLER

Nest size or nest-building activity has recently been hypothesized to be a postmating sexually selected signal in monogamous birds: females may assess a male’s parental quality and willingness to invest in reproduction by his participation in nest building. Females may thus adjust their reproductive effort (i.e. clutch size) not only to their own abilities but also to those of their mates. We i...

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