Data from: Unpredictable perturbation reduces breeding propensity regardless of pre-laying reproductive readiness in a partial capital breeder

Theoretically, individuals of migratory species should optimize reproductive investment based on a combination of timing of and body condition at arrival on the breeding grounds. A minimum threshold body mass is required to initiate reproduction, and the timing of reaching this threshold is critical because of the trade-off between delaying breeding to gain in condition against the declining value of offspring with later reproductive timing. Long-lived species have the flexibility within their life history to skip reproduction in a given year if they are unable to achieve this theoretical mass threshold. Although the decision to breed or not is an important parameter influencing population dynamics, the mechanisms underlying this decision are poorly understood. Here, we mimicked an unpredictable environmental perturbation that induced a reduction in body mass of Arctic pre-breeding (before the laying period) female common eiders (Somateria mollissima; a long-lived migratory seaduck) while controlling for individual variation in the pre-laying physiological reproductive readiness via vitellogenin (VTG) - a yolk-targeted lipoprotein. Our aim was to causally determine the interaction between body condition and pre-laying reproductive readiness (VTG) on breeding propensity by experimentally reducing body mass in treatment females. We first demonstrated that arrival body condition was a key driver of breeding propensity. Secondly, we found treatment and VTG levels interacted to influence breeding propensity, indicating that our experimental manipulation, mimicking an unpredictable food shortage, reduced breeding propensity, regardless of the degree of pre-laying physiological reproductive readiness (i.e., timing of ovarian follicles recruitment). Our experiment demonstrates that momentary environmental perturbations during the pre-breeding period can strongly affect the decision to breed, a key parameter driving population dynamics.Data from: Unpredictable Perturbation Reduces Breeding Propensity Regardless Of Pre-Laying Reproductive Readiness In A Partial Capital BreederThe data file contains information on body mass at capture (BM1) or at release (BM2), the difference between BM1 and BM2 (DIFF) the concentration of VLDL and VTG, the YEAR (2003 or 2004),the Breeding Propensity with 1 indicating a breeding bird and 0 a bird non resighted in the colony, The Treatment category (maintained 24 hours in captivity or release immediately after banding), the release date in julian date and the band number (BAND)data_Dryad.tx