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Title: Ecology of urban magpies (Pica pica L.).
Author: Tatner, Paul
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 1980
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1) This thesis concerns the ecology of urban magpies Pica pica L, as investigated in an area of South Manchester. 2) Using nest census results from an area of 47 km 2 , the density of magpies was estimated as 5.9 - 6.8 pairs km ; the principal objective of the study was to explain this high density. 3) The study area was surveyed five times between 1976 and 1979; data collected included information on the preferred nest sites, nesting density, and number of magpies present. In four of the five surveys, the birds observed accounted for 69% of the magpies estimated to be present from the number of occupied nests. Nesting density was s~own to be significantly correlated with tree diversity and area of grassland. There may have been a slight increase in the number of breeding magpies between 1977 and 1978. Average fledging success in the area was estimated, from a survey in June 1977, to be 1.5 young per pair. 4) In studying the breeding ecology between 1977 and 1979, 159 nests were investigated. The average first egg date was l7th.April, and the average clutch size was 5.5 eggs. An incubation period of 24 days was calculated from the laying of the first egg, or 18 days from the laying of the last egg, to the hatching of the first pullus. Overall 55% of the pairs investigated (if replacement clutches are included), successfully raised at least one pullus to fledging. Asynchronous hatching occurs. Of the nests in which eggs were laid, 36% failed to hatch any young. The significance of partial and total failures during the egg stage are discussed. It was necessary to calculate a range for hatching success (43% - 65%) because it was not possible to determine whether the drop in reproductive potential which occured at this time, was due to loss of eggs or nestlings. Hatching success and total failures are considered in terms of seasonal variation; differences between original and replacement clutches are also investigated. Of the nests which successfully hatched young, the average brood size at fledging was 1.9 young for the original attempts, and 1.5 in replacement attempts; 34% failed to fledge any pulli. Nestling starvation was strongly indicated as the major Cause of failure, although the effects of predation could not be ruled out. 5) The high density of magp!es in Manchester corresponds to an abnormally low breeding success. If national mortality figures apply, the population should be decreasing by 16% a year. The census figures indicated that this was not the case, therefore immigration, or a lower adult mortality occurs in Manchester. 6) Increases in magpie weight, tarsus length, and ~enth primary length during the nestling period have been described using logistic growth curves. 7) The significance of selective starvation in regulating brood size is considered for a small sample of 6 nests, which were studied in detail. This study also suggests that magpies exhibit synchronous fledging. 8) Body component growth, and overall body composition in nestling magpies may be interpreted in terms of an adaptive growth hypothesis; items which have the current highest functional priOrity grow the most rapidly. It is also shown that the growth strategy of nestling magpies exhibits all the features proposed by O'Connor (1978a) as exemplifying a typical brood reduction strategist. 9) The diets of adult and nestling magpies have been interpreted from analyses of a Variety of samples. Seasonal Variation in the availability of the invertebrate fauna is represented by the results of pit falling at two sites. The nestling and adult diets are extremely varied, but are largely composed of material that is typical of grassland habitat. 10) The main points of the investigation are brought together in the conclusion to provide some indication of why the magpie is so abundant in Manchester.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available