Survival and recruitment of mallards in relation to brood size, hatching date and wetland characteristics

Abstract

My thesis focused on the least understood period of Mallard life history from hatching to near independence from parental care. I evaluated survival of young in relation to brood size, hatching date, overland travel, wetland characteristics, and food abundance. Using field experiments, I evaluated whether clutch size of Mallards may be limited by the parent's ability to raise offspring (parental behaviour hypothesis). Clutch and brood sizes were manipulated to form reduced, control and enlarged broods. Although sample size precluded strong statistical inference, young in enlarged and reduced broods showed trends toward reduced survival. Brooding efficiency (heat transfer from a care-giving female to her ducklings) was examined under controlled conditions to evaluate whether this form of parental care could influence duckling survival under natural conditions. Duckling temperature (Td) did not differ, but variability in Td increased with brood size. To examine seasonal variation in reproductive success, I supplemented information on duckling survival on my main study area with data on recruitment to the breeding population on the St. Denis National Wildlife Area. Duckling survival was higher early in the season in years (3 of 4) with normal wetland inundation patterns. Similarly, the probability of recruitment was higher for young hatched early in the breeding season. Ducklings hatching early have more time to improve their condition and flight skills prior to migration. Therefore, I predicted that early-hatched offspring would have an additional advantage in terms of recruitment over young hatching later in the breeding season. However, I was unable to detect an additional advantage in recruitment over that associated with duckling survival. I also examined brood ecology and duckling survival in relation to overland movements and wetland characteristics. For Mallard broods with known fate, there was no relationship between duckling or brood survival and either distance traveled overland from the nest to the first pond used or total distance traveled during the first two weeks after hatching. Broods spent most of their time associated with semi-permanent wetlands and were usually located on wetlands with conductivity $