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    Sources of variability associated with Adélie penguin CEMP parameters measured at Béchervaise Island, East Antarctica

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    Document Number:
    WG-EMM-03/48
    Author(s):
    L.M. Emmerson, C. Southwell, J. Clarke and K. Kerry (Australia)
    Agenda Item(s)
    Abstract

    We examine the magnitude of a variety of sources of variability associated with CEMP parameters. The CEMP parameters considered in this paper include: A3: breeding population size, A1: arrival weights, A5: duration of foraging trips, and A7: fledgling weights. Sources of variability can generally be considered as either sampling variance or process related variance, although sometimes the two can be confounded. Temporal variability, that is the between-season variability, was consistent across parameters at around 5-7% CV. The smallest source of variability was associated with measurement error although this source of variability is difficult to assess. The largest source of variability was related to the timing of data collection which we term as the within-season variability. This ranged between 4.6% for population size up to 19.8% for fledgling weights. It would be useful to explore ways of reducing the magnitude of within-season variability because of the potential influence it has on detecting between-season changes in these parameters. This could potentially be achieved by either pooling several 5-day CEMP periods to reduce the time span over which the data are collected while simultaneously maintaining a sufficient sample size or by standardising summary statistics against some chronologically relevant event and reassessing temporal variability. Partitioning the sources of variability further than we were able to for this paper may be useful because our estimates of temporal variability incorporate within-season variability and measurement error. However, any refined estimates of variability would only affect the ability to detect long term changes in a parameter if sampling variance can also be reduced.

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