Breeding ecology and local population dynamics of lesser scaup (Aythya affinis) in boreal forest of Western Canada / Rodney W. Brook

Includes bibliographical references (leaves 97-100).

Long-term surveys indicate a decline oflesser scaup (Aythya affinis: hereafter scaup)
populations breeding in boreal forest of western Canada. Unfortunately, little is known
about the breeding ecology and population dynamics of boreal-breeding scaup,
information needed to help guide conservation efforts. Therefore, in 1999 and 2000 I
estimated demographic vital rates for a scaup population near Yellowknife, Northwest
Territories (YKSA). Female scaup were trapped before breeding and fitted with radio
transmitters and nasal markers to help estimate vital rates. Demographic rates from
YKSA were compared with those estimated on a National Wildlife Area (NW A) near
Saskatoon, Saskatchewan, and elsewhere. Despite large latitudinal differences between
study areas, clutch initiation dates were remarkably similar for both sites (YKSA range
= S June - 12 July, NW A range= 7 June - 9 July); and best-predicted Total Clutch
Volume (TCV = 492.26 - 5.93 CID). Female breeding-season apparent survival rates
were similar: YKSA (0.80) and NW A (0.82). Analysis of projection models indicated
the YKSA population was near stability (population growth rate (A.)= 0. 979) during
1989 to 1998 and in sharp decline (A.= 0. 754) in 1999 and 2000. A detailed
parameterization of the model for the recent period indicated a similar decline (A.=
0.831 ). For all models, the largest changes in A. were due to changes in breeding-season
and non-breeding-season survival. Nesting success was also important and, from
simulation analyses, all three rates together explained about 90% of the variation in/....
Population cycles of snowshoe hare (Lepus americanus), other small mammals, and
their predators have a strong influence on the population dynamics of several resident
species of birds and mammals in boreal forest. This, a possible explanation for large
annual fluctuations in scaup productivity, was identified from correlations between
estimates of scaup productivity and indices of predator abundance (as indexed by hare
density [r = -0. 79]) and buffer prey abundance (indexed by populations of microtines [ r
= 0.69]). Predation may synchronize oscillations of sympatric prey through mechanisms
predicted by the shared prey (hares) and (or) alternate prey (microtine) hypotheses.
Further research is needed to improve estimates of scaup demographic rates and
determine the importance of extrinsic factors (e.g., predators, food, weather and harvest)
that potentially limit boreal scaup populations.