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The late spring and slimmer diet of blue grouse on lowland breeding ranges on Vancouver Island was determined by examination of the contents of 875 crops taken from birds collected on 3 study areas in the years 1950 through 1952 and 1957 through 1966. The spring and early summer diet of males was mostly conifer needles, while adult females ate mainly leaf material and flowers during the same period. The food of chicks was mainly invertebrates until the birds reached the age of approximately three weeks, at which time plant material formed the greater portion of the diet. In late summer the diet of both adult and juvenile grouse was primarily fruits and seeds of trailing blackberry, salal, huckleberry, and other plants. Selection of plant foods occurred at the time of ovulation and moult. As a result, the protein and mineral content of the diet was highest during periods of greatest need. No apparent differences in the spring diet of females were found which could be related to poor early survival of chicks, or to a delayed hatch in 1962. The various food types were eaten in similar relative proportions by adult and yearling grouse, and differences in reproductive performance of these two age classes could not be related to the diet of the grouse. The altitudinal migration of blue grouse in late summer and autumn does not appear to be related to the availability or condition of the food supply at the time of departure of the birds. / Science, Faculty of / Zoology, Department of / Graduate

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The breeding and feeding ecology of the Swallow, Hirundo rustica, and the Sand Martin, R. riparia, in Central Scotland is described, with particular reference to the constraints imposed by environmental conditions. The time and energy investment in reproduction was examined for all stages of the breeding season in a wide variety of environmental conditions. Brood sizes were manipulated to change the investment of each parent in the brood. The D2018 technique was used to measure flight costs (0.0848 kcal g-l h-1 for the Swallow, 0.1288 kcal g-l h-1 for the Sand Martin) and the rate at which each species collected food under a variety of conditions was examined (mean values were 0.14 assimilable kcal min-1 for the Swallow, 0.05 assimilable kcal min-1 for the Sand Martin). These data, along with measurements of the nestlings' daily energy requirements, were used to investigate energy balance and the consequences for the timing and level of each breeding attempt. It is suggested that the Swallow lays later than the Sand Martin because (a) it takes larger insects and does not lay until these become abundant and (b) the female Swallow incubates alone whereas both Sand Martin sexes incubate, hence the Swallow defers laying until the risk of encountering bad weather during incubation is low. On 65% of the days on which measurements were made Sand Martins were unable to feed adequately a brood of five or more nestlings (31% of days for the Swallow) because foraging rates were depressed by bad weather. The risk of encountering bad weather is thus likely to limit the upper level of brood size. Energetics data are used to show that parents feeding nestlings maximise the net intake rate of energy rather than that of nutrients (protein, sulphur or calcium). The Swallow's diet includes nonpreferred small items, especially when these are relatively abundant, even when the preferred large items are available - contrary to predictions of optimal foraging models. It is shown, however, that foraging effiency is high when small items are taken. In agreement with central place foraging theory the bolus size of Sand Martins is mainly determined by the distance travelled to the feeding site. This is not always the case, however, since patch and prey quality and the search methods employed have a greater influence on the bolus size of the Swallow. Overall, the study allowed the scope for breeding activity for hirundines under different conditions to be defined and showed the importance of each species' reproductive and foraging strategies in optimising the number of offspring produced.

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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.

From work previously done by John Ward, it was shown that the productivity on Cleland Island was greater than that on Mandarte Island. The mean weight and fledging rate for all brood sizes from one to six, was higher on Cleland Island. It was thought that an analysis of the parental feeding system and a comparison of the feeding biology would provide a partial explanation for the difference in productivity between Mandarte and Cleland Islands. The main objectives of this comparative study were to distinguish between the ration requested by the chicks, i.e., parental feeding system, and the ration received by the chicks, i.e., how the feeding biology modifies the ration. Both the quality and quantity of foods given to the chicks differ between the two colonies. Mandarte adults eat a greater variety of foods than the Cleland adults. The observations of courtship feeding and the collections of stomach contents, show that Mandarte adults eat garbage, intertidal organisms, and fish, whereas Cleland gulls eat fish and intertidal organisms. If courtship feedings do significantly contribute to the requirements for egg production, the superior quality of food given to the Cleland females may be correlated with the higher hatching success on Cleland. In addition to the effect on the hatching success, the quality of food may also influence the fledging success. On both Mandarte and Cleland, the adult's food differs from the chick's food. Initially, the Mandarte chick predominantly receives fish but as the chick stage progresses, less fish and more garbage is given to the chicks. This deterioration in the quality of the foods may be correlated with the low fledging success of chicks raised late in the season. Cleland' s chicks receive only fish throughout the parental period so that chick mortality could not be associated with a change in the quality of the food. The lower fledging rate recorded for Mandarte chicks may also be associated with the smaller quantities of food given to the chicks. Although no significant difference exists, the weight of food given to the Cleland chicks exceeds that given to the Mandarte chicks. Some of the differences of quality and quantity of food may be explained by the temporal and spatial patterns of food availability. The parental feeding frequency is thought to be dependent on the needs of the chicks but is modified by prey availability. Parental feeding frequency reaches a peak in the early morning, afternoon, and evening on Mandarte but is relatively constant until just before dusk on Cleland Island. The sandlance, obtainable in the immediate vicinity of Cleland, is available throughout the day; the herring, rarely caught near Mandarte Island, has a periodic availability during the day. A Mandarte adult, seeking an alternate food during a period of low herring availability, may have to make a long trip to some garbage dump or intertidal zone. Not only the patterns of feeding activity but also the total feeding activity differ between the colonies. The frequency of feeding after a trip is similar for both colonies but the foraging frequency is significantly greater for Mandarte parents. This may mean that the Mandarte parent presents fewer feedings than Cleland adults from the catch of one foraging trip. Although parents from both colonies increased the foraging and feeding frequency when chicks were added to normal broods, neither Mandarte nor Cleland adults increased the feeding frequency in direct proportion to the brood size. The adjustments made in the foraging and feeding frequency are made possible through a series of signals constituting the parental feeding control system. The control of parental feeding is achieved through the use of two signals, calling and pecking. A functional relationship exists between the hunger level and the call frequency, peck frequency, and call intensity. For any hunger level the frequency and amplitude of the call change with age but the pecking response does not change with the chick's age. From the field observations of feeding, it is evident that a particular cumlative pecking value and call frequency elicits a feeding and the change in call amplitude associated with satiation is instrumental in terminating a feeding. The foraging frequency, proportional to the brood size, may be modulated by the cumulative calling of the chicks. A simple experiment did show that the activity of the parent is influenced by the hunger of the brood; this fact was demonstrated by an experiment in which I satiated the gull chicks thus increasing the time that the parents remained on the territory. In summary, the feeding frequency is adjusted by the pecking and calling frequency while the foraging frequency of the parents is adjusted by the cumulative calling of the chicks. A feeding is initiated by a specific calling frequency and cumulative pecking value and terminated when the food is consumed or when the call amplitude indicates satiation. The ability of the parents to adjust their feeding activity raises some interesting questions. The relationship of both the feeding biology and parental feeding system to the productivity of an island is discussed from a comparative viewpoint. The importance of the feeding system and other factors is discussed in relation to the evolution of clutch size. / Science, Faculty of / Zoology, Department of / Graduate

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No description available.