How important is it to standardise the measured mass of shorebirds weighed at varying intervals after capture?
Author(s): Clark, J.A., Gillings, S., Clark, N.A., Cole, K.B., Breese, G., Woods, J.L., Bellman, H.A. & Robinson, R.A.
Published: April 2023
Journal: Wader Study Volume: 130 ( part 1 )
Digital Identifier No. (DOI): 10.18194/ws.00297
This paper examines this phenomenon using captures of Knot, Turnstone, Dunlin and Semipalmated Sandpiper in Delaware Bay, USA. As these waders were caught whilst actively feeding on the eggs of Horseshoe Crabs, there was the possibility that birds weighed first could be heavier due to having a gut full of eggs, whilst those weighed last may have digested/voided their gut contents prior to being weighed and so weigh relatively less. For sample bird catches birds were weighed repeatedly, from immediately after capture to up to four hours after capture.
The study found that birds rapidly lost up to 5% of their body weight in the first 30 minutes, with weight loss much reduced thereafter. This weight loss was strongly correlated to the number of droppings birds produced in the keeping pens, indicating the reduction was related to processing of gut contents. The paper shows how body weights can be standardised to that expected if each bird was weighed at 30 minutes after capture. For large catches this can increase the apparent mean weight for the sample by up to 2%. The paper also discusses the situations in which standardising body weight measurements for time from capture may be necessary.
NotesThe authors thank all those involved in the catches in Delaware from which these data were gathered, and especially Dave Carter whose energy and enthusiasm established the work in Delaware. They would also like to thank Sarah Dawkins and Ian Henderson for their help with the mass loss samples. This work was funded by Delaware Department of Natural Resources and Environmental Control through a series of contracts over the years 2001–03.
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