BIRDS LESSER SCAUP AND RACCOONS: ARE THERE LINKS IN SOUTHWESTERN MANITOBA? Gord Hammell P.O. Box 37, Erickson, MB, ROJ 0P0; E-mail: <[email protected]> ABSTRACT was uncertain given available data. Raccoons (Procyon lotor) invaded the However, there was a detectable shift southern prairie provinces of Canada in hatching chronology to later dates in during the mid-1990s and became a years with wetter summers. It is possible significant predator of waterfowl nests. that the shift in hatching chronology could Nest predation by this novel predator be related to raccoon predation of scaup may alter the reproductive success, and nests and changes in renesting rates thereby the population size of waterfowl among time periods, but it is impossible like the lesser scaup (Aythya affinis). to say for sure given the available data. However, it is difficult to evaluate the Nevertheless, such a shift may have been effects of raccoon predation relative to detrimental to local populations over the other factors that affect scaup populations. years, as later-hatched ducklings have a To investigate possible links between lower probability of recruitment into the raccoons and lesser scaup, a species with breeding population. declining populations, I examined results from studies conducted in southwestern INTRODUCTION Manitoba before (1950’s) and after Lesser scaup (Aythya affinis) are (1970’s) the arrival of the raccoon. medium-sized diving ducks that breed Specifically, I attempted to detect possible in the boreal forests and parklands changes in scaup breeding population from Alaska to Manitoba.1 In breeding size, reproductive success, and hatching plumage, males are black and white and chronology that might be related to the females are dark chocolate brown with arrival of raccoons. I hypothesized that a white face patch (Fig. 1, see inside the post-raccoon period would show: front cover, bottom). Combined North (a) decreasing local scaup breeding American breeding populations of lesser populations due to lower recruitment scaup and similar-looking greater scaup as a result of decreased nest success (A marila) have been declining from highs and female survival and (b) a shift in the in the 1970s of 5-7 million birds to lows of mean hatching date to later in the season 3-4 million in the 2000s (Fig. 2).2 Lesser because of increased nest losses and scaup comprise -90% of the combined more renesting attempts by female scaup. population;1 most of the decline has been Local breeding populations appeared attributed to this species, especially within unchanged before and after raccoon the Canadian western boreal forest, arrival, providing no strong evidence of where most of these birds breed.3 Lesser an impact on numbers of adult birds. The scaup (but not greater scaup) breed in extent of change to reproductive success south-western Manitoba parkland, and 54 UNIVERSil Y LIBRARY Blue Jay UNIVERSITY OF ALBERTA Figure 2. Breeding population estimates, 95% confidence intervals, and North American Waterfowl Plan goal (dashed line) for scaup (lesser and greater) in the traditional survey area (strata 1-18, 20-50, 75-77). long-term but less consistent declines Territories.4-13 The major factor responsible in breeding pairs have also been noted for waterfowl nest failure and female there.34 Several hypotheses have been and duckling mortality on the breeding presented to explain declining lesser grounds is predation,114-16 so predation scaup (hereafter scaup) populations, may be an important factor (but not including changes to food resources necessarily the only factor) in explaining in wintering and migration habitats,57 reduced recruitment. Therefore, changes chemical contaminant exposure,18'11 to the local predator community (size or climate changes affecting boreal forest composition) might contribute to changes wetlands,3 lower female survival,312 and at the local scaup population level.1718 fewer immature birds relative to adults in human harvests (declining age ratio).3 The parkland area of southern However, no clear explanation for the Manitoba experienced a change to the decline has been determined. Declining predator community with the invasion age ratios in the harvest are suggestive of the raccoon (Procyon lotor) during of reduced recruitment, and contributing the mid 1900s.19 Raccoons have the factors could be any combination of potential to be a significant predator of reduced breeding propensity, reduced scaup nests, but not females,20 because clutch size and renesting rates among they search for prey in the upland and hens, or decreased nest and/or juvenile emergent vegetation zones adjacent survival.3 Reduced nest, juvenile, and to ponds,2122 where most scaup nests female survival have been suggested as are found.23-27 Previous studies have proximate causes of decline in local scaup reported that raccoons are indeed a populations in south-western Manitoba major predator of scaup nests in south¬ and in the boreal forest of the Northwest western Manitoba.2328 In this area, more 69 (2) June 2011 55 than 50% of scaup nest over water (nest still some merit in testing my predictions surrounded by water), and more of these to determine whether any of them are nests are successful than are dry-land substantiated. nests.2327 Over-water nests, which may be isolated from dry-land predators for The Consensus Report of the Second some or all of the incubation period, Scaup Workshop indicated several priority presumably would be more vulnerable to research topics, one of which was the raccoons because of their nest-searching establishment of retrospective analyses behaviour. Thus, the arrival of raccoons to examine patterns over time and may have resulted in increased nest space.31 Analyses of existing data were losses, reduced productivity and reduced considered the most immediate research juvenile recruitment. Also, if initial nests need because results are critical for are destroyed, some scaup do attempt forming hypotheses, organizing research second nests (renests) depending on projects, and securing funding. With female age and habitat conditions.28 this priority in mind, and to evaluate the This increased nesting effort resulting novel predator hypothesis, I conducted a from increased initial nest destruction retrospective analysis of existing scaup can lead to greater nest-site exposure breeding pairs, productivity (broods to predators (e.g., fox [Vulpes vulpes] per pair or nest success) and hatching and mink [Mustela vison]) and increased chronology data from studies conducted female mortality.14-29 Scaup exhibit natal in south-western Manitoba prior to the philopatry and breeding-site fidelity,128 1980s, which was prior to the decline so reduced juvenile recruitment and of the continental scaup population. I increased female nest-site mortality focused primarily on the area of Erickson, might result in a smaller local breeding Manitoba ( 50° 30’ N, 99° 55’ W ). My population. Long-term studies of a different main objective was to determine whether species, the canvasback (A. valisineria), in changes in reproductive parameters southern Manitoba have shown that with occurred after the arrival of the raccoon. increasing raccoon numbers, nest losses Erickson is well-suited to this analysis increased and productivity decreased.30 because several historical studies cover The extent of canvasback renesting was appropriate time periods (Rogers study: thought to be closely related to predation. 1957-1960;24’32'33’ Hammell study: 1970- Consequently, for scaup I hypothesized 1972,23 [and unpublished data]; and that the arrival of raccoons as a novel Afton study: 1977-8028). All three studies predator in southern Manitoba affected were conducted at the same locale, and scaup populations at the local level. the raccoon arrival time is known and Based on this hypothesis, I predicted: occurred outside of a drought period, (a) a decrease in the size of the breeding eliminating the severe confounding population over time due to lower juvenile factor of drought on scaup populations recruitment as a result of decreased nest and reproduction.24 In addition, aerial success and female survival, and (b) a photos and discussions with the local shift in mean hatching date to later in the community suggested that agricultural season because of increased nest losses impact (amount of cultivated, hayed, or and more renesting attempts by female pastured land) in the study area was scaup. Importantly, these predictions similar across the different time periods, are not unique to the novel predator thereby controlling for major habitat hypothesis and could apply to any number change as a factor affecting the results. of alternatives based on other factors During the 10-year interval between the affecting reproduction. However, there is earlier studies (1960-1970), raccoons 56 Blue Jay Figure 3. Field study sites (denoted by the small black squares). Shaded area within expanded map represents intensively studied area near Erickson, MB. were noticed for the first time (mid- of south-western Manitoba (Fig. 3) and 1960s) by local residents in the Erickson comprises 259 ha for the 1957-60 study, area. There was no evidence found 680 ha for the 1970-72 study, and 777 that raccoons were a predator of scaup ha for the 1977-80 study. The two former during the 1957-60 study (J.P. Rogers, areas are situated entirely or mostly within pers. comm.). However, they were a the larger area. These block areas were major predator at Erickson by the early most intensively studied, but additional 1970s.23 data were collected from larger lakes and along roadside transects in the Erickson METHODS area of approximately 80 km (1957-60) Study Area and 71 km (1970-72). The topography is The study area for all three time periods rolling with numerous ponds and lakes. is situated in the parkland pothole region The uplands are a mixture of lands sown 69 (2) June 2011 57 to cereal and oilseed crops, hay, pasture, data.28 Care was taken by investigators to and native woodland.