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No description available.

This project describes various aspects of the breeding ecology and behaviour of the brown falcon Falco berigora, a common but poorly study Australian raptor. In particular it examines (a) the main influences on reproductive success; (b) tests predictions of theories proposed to explain the evolution and maintenance of sexual size dimorphism (RSD; females the larger sex) in raptors; and (c) investigates sex allocation patterns in the light of current sex ratio and parental investment theory. The study was conducted between July 1999 and June 2002 approximately 35 km southwest of Melbourne, at the Western Treatment Plant (WTP), Werribee (38°0’S 144°34’E) and surrounds, a total area of approximately 150 km2.¶ · In all plumage and bare part colouration of 160 free-flying falcons was described. The majority of variation in these characters could be attributed to distinct age and/or sex differences as opposed to previously described colour ‘morphs’.¶ · Nestling chronology and development is described and formulae based on wing length derived for determining nestling age. An accurate field-based test for determining nestling sex at banding age is also presented.¶ · Strong sex role differentiation was apparent during breeding; typical of falcons females performed most parental duties whilst males predominantly hunted for their brood and partner. Based on observations of marked individuals, both sexes of brown falcons aggressively defended mutual territories throughout the year, with just 10% of each sex changing territories during the entire study period. Males performed territorial displays more frequently than females, the latter rarely displaying alone.¶ · The diet of the population as a whole was very broad, but within pairs both sexes predominantly specialised on either lagomorphs, small ground prey (e.g. house mice Mus musculus), small birds, large birds or reptiles, according to availability.¶ · Reproductive parameters such as clutch size and the duration of parental care were constant across all years, however marked annual differences in brood size and the proportion of pairs breeding were evident.¶ · Age was an important influence upon reproductive success and survival, with immature birds inferior to adults in both areas. However, interannual differences were by far the most influential factor on breeding success and female survival. Heavy rain downpours were implicated as the main determinant of reproductive success and adult female mortality in a population largely devoid of predation or human interference.¶ · Female-female competition for territorial vacancies was intense; larger adult females were more likely to be recruited and once breeding fledged more offspring. In contrast, male recruitment and breeding success was unrelated to either body size or condition indices, although smaller immature males were more likely to survive to the next breeding season. This directional selection is consistent only with the predictions of the intrasexual competition hypothesis.¶ · Despite marked RSD (males c. 75% of female body mass), throughout the nestling phase female nestlings did not require greater quantities of food than their male siblings. However, female parents fed their last-hatched sons but not daughters, resulting in the complete mortality of all last-hatched female offspring in focal nests. Given last-hatched nestlings suffered markedly reduced growth rates and female, but not male, body size is important in determining recruitment patterns, the biased allocation amongst last-hatched offspring is likely to reflect differing benefits associated with investing in small members of each sex, consistent with broad-scale Trivers-Willard effects. Recruitment patterns support this, with surviving last-hatched females, in contrast to males, unable to gain recruitment into the breeding population upon their return to the study site.¶ Thus selection appears to act at the nestling, immature and adult stages to maintain RSD in the focal population. Larger females were favoured in the nestling phase, at recruitment and once breeding had greater reproductive success. In contrast, selection favoured a reduction or maintenance of immature male size as smaller birds had a greater chance of survival in the year following recruitment than their larger counterparts; thereafter male size was unimportant. Together, this directional selection favouring increased female competitive ability is consistent only with the predictions of the intrasexual competition hypothesis, which appears the most probable in explaining the maintenance and perhaps evolution of RSD in raptors.

Understanding the patterns and processes that create differences among individuals in components of fitness, like the probability of survival or reproductive rates, is essential to our knowledge of population dynamics and for informing conservation efforts. For organisms in seasonal environments, early-breeding individuals regularly attain higher fitness than their late-breeding counterparts. Two primary hypotheses, related to quality and date, have been proposed to explain lower reproductive success of late breeders, but the veracity of these ideas has not been fully resolved. I tested predictions associated with these hypotheses to assess the effects of indices of parental and environmental quality on nestling quality and survival in an insectivorous passerine, the tree swallow (Tachycineta bicolor), at two widely separated breeding locations in western Canada. I combined experiments and statistical modelling of observational data to evaluate two mechanisms proposed to contribute to seasonal decline in environmental quality: an increase in nest parasite abundance and a decrease in food abundance with later breeding dates. A parasite reduction experiment revealed a disproportionate benefit of parasite removal on length of primary feather for early-hatched nestlings, suggesting greater energetic constraints early in the breeding season. Furthermore, late-hatched nestlings from parasite-reduced nests had longer head-bill lengths than their control counterparts, and developed head-bills of similar length to those of early-hatched nestlings. Other than these findings, there were few detectable effects of parasites on nestling size, growth and immunity, as has been reported from several previous studies. Indeed, negative effects of parasites were only apparent when food (i.e., insect) biomass was considered. In a second series of experiments in which parental quality was controlled, I also tested whether food abundance declined during the breeding season, as predicted if environmental conditions deteriorate seasonally (i.e., date). Reduced reproductive success of late-breeding individuals was causally related to a seasonal decline in environmental quality. Declining insect biomass and enlarged brood sizes resulted in nestlings that were lighter, in poorer body condition, had shorter head-bills, shorter and slower growing ninth primary feathers and that were less likely to survive to fledge. Next, I asked whether results obtained from long-term mark-recapture data corroborated findings of short-term manipulations. I examined seasonal variation in first-year apparent survival to investigate the relative influence of large-, small- and individual-scale factors associated with the quality and date hypotheses. Although parental quality was an important predictor of first-year apparent survival of tree swallows, my results further suggested that quality of parents was not the primary factor influencing seasonal variation in first-year apparent survival. Rather, findings were most consistent with the date hypothesis. The relationship between apparent survival and a direct measurement of environmental quality indicated that annual variation in moisture had important consequences for first-year apparent survival of tree swallows in Saskatchewan. First-year apparent survival probabilities were higher during wet years and wetter conditions are generally linked to greater insect abundance. In British Columbia, nestlings from larger broods were less likely to survive, possibly as a result of receiving less food. Apparent survival probabilities were also higher when food was more abundant. I demonstrated that both parental and environmental quality influenced seasonal variation in fitness-related traits of tree swallows. However, the strongest evidence suggests that environmental quality, and in particular food abundance, had the greatest effect on seasonal variation in nestling quality, reproductive success and first-year apparent survival in tree swallows. My results highlight the importance of considering regional precipitation trends when projecting effects of climate change on demography of aerial insectivores.