Second North American Sea Duck Conference - Patuxent Wildlife ...

SECOND NORTH AMERICAN SEA DUCK CONFERENCE
MULTISTATE MODELING OF BROOD AMALGAMATION
IN WHITE-WINGED SCOTERS
Joshua J. Traylor¹, Ray T. Alisauskas 1, 2, and F. Patrick Kehoe 3
¹Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, Saskatchewan,
Canada, S7N 5E2; Joshua.traylor@ec.gc.ca
²Prairie and Northern Wildlife Research Center, Canadian Wildlife Service, 115 Perimeter Road,
Saskatoon, Saskatchewan, Canada, S7N 0X4
3 Ducks Unlimited Canada, #200 10720-178 St., Edmonton, Alberta, Canada, T5S 1J3
Female waterfowl can lose or abandon offspring after hatch often leading to the phenomena of posthatch
brood amalgamation (PHBA). The potential fitness implications that arise from this behavior
has brought about considerable debate on physiological or ecological motivations for PHBA of
young, and potential costs and benefits of ducklings brooded in amalgamated broods. We explored
relationships between probabilities of movements from maternal to amalgamated broods using a
population of individually marked white-winged scoters (Melanitta fusca deglandi) (i.e., females [n
= 94] and offspring [n = 664]) , at Redberry Lake, Saskatchewan, Canada, and pertinent ecological
covariates utilizing multistate modeling. We tested hypotheses about movement probabilities and
hatch date, brood size, female size and condition, duckling size and condition, and weather. We
assigned ducklings as either (M) in broods with natal mothers, or (F) in foster broods cared for by
a foster mother and conspecific non-siblings, focusing on covariates of movement probability to
foster broods. Results showed that most fostering occurred within four days of hatch; additionally,
likelihood of fostering was positively related to inclement weather, and negatively related to hatch
date, female condition at hatch, female size, initial brood size, and duckling condition. Use of
multistate modeling enabled proper estimation of relationships between likelihood of duckling
adoption and numerous ecological variables. We conclude PHBA in this population appears to
be consistent with several hypotheses (i.e., accidental mixing, energetic stress, and brood size and
success hypotheses), although it is probably a complex function of numerous factors that vary year
to year. Because the importance of predation in motivating abandonment or adoption of ducklings
remains equivocal, we discuss how duckling traits, in a population located near high gull densities,
may provide insights into the relative importance of predation to PHBA.
66 ANNAPOLIS, MARYLAND, USA NOV. 7-11, 2005