Fat scoring in four sparrow species as an estimation of body condition: a validation study

Abstract

Body condition indices are used to assess individual health of wild and captive animals. The definition of body condition varies by researcher and study goals but typically refers to measures of energy reserves; most commonly fat stores (Labocha & Hayes, 2012) . In avian biology, body condition has been correlated with individual survivability (Blums et al ., 2005), reproduction (Chastel et al ., 1995; Bêty et al ., 2003) migration (Bêty et al ., 2003; McWilliams et al ., 2004; Laursen et al ., 2019), and habitat quality (Angelier et al ., 2011; Balbontín et al ., 2012). One of the oldest and most common methods of determining avian body condition is fat scoring: using a qualitative scale to score visible subcutaneous fat (Blanchard, 1941; Helms & Drury, 1960). Scores are determined by using the fullness and color of furcular and/or abdominal regions of a bird to estimate fat reserve size and can be determined in under a minute. Fat pad size and fat score are highly correlated, making this a quick and effective means of determining body condition (Kaiser, 1993; Labocha & Hayes, 2012). Fat score can be used in tandem with other morphological measurements to more accurately predict fat mass (Labocha & Hayes, 2012; McWilliams & Whitman, 2013). However, it is important to note that fat score is a qualitative measurement, and therefore subjective, and there is not one single scale used (Rogers, 2003; Labocha & Hayes, 2012; McWilliams & Whitman, 2013). Furthermore, not all bird species carry fat in the same manner (Seewagen, 2008; Schamber et al .,