The predation strategies of four species of aerial feeding bird, the Swallow, Hirundo rustica, Sand Martin, Riparia riparia, House Martin, Delichon urbica and Swift, Apus apus, are examined during their breeding season in Britain. The abundance of aerial insects upon which they feed increases in April and reaches a plateau in May which is maintained until September. Aerial insect density is higher nearer the ground, the spring rise in abundance occurs earlier, a greater proportion of larger insects are available and insect numbers fluctuate less than at higher levels. The arrival times of the different predator species into the breeding area are staggered and this is linked to their preferred prey and feeding station, and to the distribution of aerial insects. Throughout the breeding season the four species of bird are ecologically isolated with respect to feeding station in the air-space and various characters of the insect prey, primarily size and mobility. It is suggested that to coexist they segregate along a combination of axes of the feeding niche, although segregation in air-space may be the most effective. Morphological adaptation to feeding niche is shown for tail shape, wing-length and bill shape, which respectively influence manoeuvrability, mode of flight and prey handling ability of the predators. Both Sand Martin and Swallow show increases in their prey size and mobility niche breadths in favourable feeding conditions whilst all four species simultaneously show decreases in air-space niche breadths. It is postulated that both within and between species there is a tendency to switch between patch specialisation and prey specialisation. Current theories of optimal patch and prey choice are discussed in relation to this hypothesis. Under very adverse conditions prey size overlaps are small and, when they increase, air-space overlaps simultaneously decrease. This suggests competition between aerial feeding birds in adverse conditions. Swallows deliver more meals per unit time to larger broods, with an increase in the feeding rate of the male most evident. Males also increase their feeding rate to second broods, but these receive the same amount of food as first broods indicating a seasonal decline in meal size. There is a seasonal decline in size of prey items even though a higher density of available large (> 5 mm body length) insects occurs during second brood feeding. It is shown that the largest insects are in patches too far from second brood nests to be profitable. For first and second broods an optimal foraging strategy is to choose patches with the largest mean insect size, if the patches are within a given distance from the nest. Selection of an optimal size for fast-flying taxa is influenced by time and energy costs of pursuit. It is suggested that rearing larger than normal broods is constrained by the requirement of equal parental investment and the extra reproductive cost likely to be incurred by the male bird. Based on a very small sample of nests it is tentatively suggested that in colonial nesting Sand Martins there is an advantage in nesting early, with more birds feeding communally to aid location of food concentrations. Because individuals with centrally placed burrows are more able to minimise time spent deterring predators, and because early centre nesters suffer less time loss through competition at the nest-site, these same individuals have more time for locating other feeding birds and food concentrations. Thus the early season, centre colony nesters may collect more food per unit time and raise more off-spring. Comparison of aerial feeding bird communities in three zoogeographical regions indicates that selection for characters contributing to mode of flight and manoeuvrability are more important than selection for bill character. In Africa the Palearctic species maintain essentially the same feeding stations as in their breeding season although the air-space niche breadths show contraction and overlap is reduced except between Swift and House Martin. The indigenous species have different feeding stations and small air-space niche breadths, and where overlap is high the species involved apparently do not breed during the "winter" of the Palearctic species, possibly because of food shortage. The prey size niche breadth of the Swallow, H. rustica is very similar between Britain and Africa. With many more species utilizing this niche axis, compensation is likely along another axis, probably air-space.

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Pigeon's working memory for event duration was investigated using variations of the delayed matching to sample procedure. When a retention interval of variable length was interposed between the sample and comparison stimuli, pigeons responded as though a long-duration sample had been short after retention intervals of 10 sec or greater. This "choose short" effect occurred reliably in each subject, regardless of whether the subject was naive or experienced, whether the sample durations were represented by food-access or light, or whether a two- or three-choice procedure was used. In order to account for these findings, a "subjective shortening" model of memory for event duration was proposed. According to the model, the choose short effect is produced by a discrepancy between a relatively static reference memory of the sample durations and a dynamic working memory of the sample durations that "shortens" over the retention interval. This discrepancy produces the tendency to respond as though the long sample was short, A number of predictions, derived from the subjective shortening model, were confirmed in subsequent experiments. First, after a long retention interval, the point of subjective equality between the short and long samples shifted to a longer duration. Second, stepwise increases in the retention interval produced a temporary choose short effect, whereas stepwise decreases in the retention interval produced a temporary choose long effect. Third, with extended training at a given retention interval, the choose short and choose long effects diminished and overall accuracy improved. These results provided strong support for the subjective shortening model, whereas they could not be interpreted readily within the context of other conceptualizations of working memory processes. / Arts, Faculty of / Psychology, Department of / Graduate

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LD2668 .T4 1966 C42 / Master of Science

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Field studies were conducted with "three species of passerine, in order to investigate the possibility that an energetic constraint limits reproduction during incubation. Swallows (Hirundo rustiea), Dippers (Cinelus einelus) and Great Tits (Parus nlajor) were studied at sites in Central Scotland. All three species exhibit gynelateral intermittent incubation, so time and energy must be allocated between the conflicting demands of reproduction and selfmaintenance. An assessment of incubation ability in the Swallow was conducted by the manipulation of clutch size during incubation. There was evidence of a clutch size dependent cost, as the duration of the incubation period was prolonged for enlarged (15.6d) compared to reduced (14.8d) clutches. The proportion of eggs hatching successfully was also lower in enlarged (81 %) than in reduced (92%) clutches, though enlarged clutches still produced the greatest number of hatched young. Clutch manipulation did not influence patterns of nest attendance, or female body condition. No effects of incubation effort were detected posthatch on either parents or offspring. The effects of clutch size on field metabolism during incubation were investigated in the Dipper. Clutch size was manipulated and energy use measured by means of the doubly labelled water technique. The results were combined with previous data collected for incubating Dippers. The field metabolic rate of 33 incubating females averaged 5.41 ± 1.34 cm3 CO2 g-l h-1 , equivalent to a daily energy expenditure of 211.52" ± 51.25kJ ind-1 d-1 , e.3 times the basal metabolic rate. Clutch enlargement resulted in an increase in energy use to 4-6 times basal metabolism for some birds," but not for others. While the mean energy use did not differ between groups, the variation amongst birds was significantly greater for enlarged than control clutches. Energy use was also influenced by river flow rates, the duration of incubation sessions and behaviour during incubation recesses. Manipulation of the energy budget of incubating Great Tits was achieved by the reduction of thermoregulatory demands. Treated nest boxes were supplied with additional heat during the hours of darkness, resulting in an elevation of nest air temperature of e.4°C above the corresponding temperature for a control group, lasting for a period of 9 hours. This produced an estimated energetic saving of 10kJ per night. Heated birds increased the duration of both the ~period of continuous incubation overnight and of incubation sessions throughout the following day, resulting in an additional 51 minutes per day spent incubating compared to the control group. The metabolic rate of22 incubating Great Tits was 7.79 ± 2.43 cm3 C02 g-1 h- 1 , or 106.4 ± 32.2 kJ ind-1 d- 1 , equivalent to e.3 times basal metabolism. Energy use escalated for control, but not for heated birds at low ambient temperatures. The importance of reserve storage and utilisation, and of provisioning by the mate were evaluated in each species. A combined hypothesis was proposed to account for body condition during incubation, incorporating elements of programmed reserve utilisation, mass adjustment, maintenance of an insurance reserve and reproductive stress. In summary, the study found "evidence of an energetic constraint acting during incubation in these species." Energy use increased in a probabilistic manner with increasing clutch size, such that birds with large clutches increased their risk of being unable to incubate the entire clutch successfully. It was suggested that such a constraint could contribute to the determination of an upper limit for avian clutch size.

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