BRANTA — Norman V. McCanch
Ornithological Studies from the Calf of Man
Institution: University of Liverpool, UK
Supervisors: JP Thorpe
Details: PhD 1999 (Completed)
Address: 23 New Street, Ash, Canterbury, Kent CT3 2BH (Oct 2005) Email
Subject Keywords: Calf of Man, breeding biology, population studies, migration
Species Keywords: European Shag Phalacrocorax aristotelis, Eurasian Sparrowhawk Accipiter nisus, Red-billed Chough Phyrrhocorax pyrrhocorax, Phylloscopus spp.
This thesis records field research on some aspects of the ornithology of the Calf of Man and the subsequent analysis of results from that research in the context of material collected by the Calf of Man bird observatory over a preceding period of thirty-five years. The aims of this work are to investigate aspects of the breeding biology, population dynamics, mortality, dispersal and migration of selected species and groups and, where possible, to use the observatory archive to place contemporary observations in a historical context.
This study has shown that archive data are valid for comparisons between years on the Calf and also to compare observed trends in Calf data with those from other islands, and nationally collected infonnation. However, it may be necessary to apply constraints to the archive data to make it directly comparable to contemporary research.
Many aspects of Shag breeding biology recorded on the Calf match data from other colonies. However, unlike birds from other colonies Calf Shags show remarkable site fidelity, and their dispersal appears to be strongly influenced by coastal topography. Adult shags from the Calf also show a tendency for post- breeding dispersal which contrasts with the trend at other sites. Key mortality parameters are very similar for the Calf and the other colonies. Biometric data collected during this study allows nestling shags to be aged with a high degree of confidence from total head measurements.
Earlier research on the Chough on the Calf appeared to show a significant correlation between the level of sheep grazing and chough population dynamics. The influence of sheep on Chough ecology wss re assessed, and this showed that earlier research had not considered the role of rabbits in the maintenance of the short grassland preferred by foraging Choughs. Combined sheep and rabbit grazing is a significant factor in Chough breeding success.
Fluctuations in breeding landbird numbers have been explained as the result of a range of proximate factors. This study shows that the main underlying influence through the period has been the effects of the cessation of farming and the subsequent changes in land-use. Calf landbird populations are also influenced by external factors such as weather and climate change, while some changes on the Calf appear to reflect factors which influence wider UK populations. In general, population changes on the Calf reflect changes in the Isle of Man population, and it may be appropriate to consider these fluctuations in a meta-population model.
The most recent Manx avifauna suggested that Sparrowhawks recorded on the Calf originated from the Isle of Man, and reflected the success of the Max breeding population. This study has shown that locally bred young probably reach the Calf during post-juvenile dispersal, together with birds from elsewhere in the British Isles, while migrants from Scandinavia pass through the Calf in both autumn and spring. It is not possible to make any inferences about the success of the Manx breeding population of Sparrowhawks from passage data collected on the Calf of Man.
Members of the genus Phylloscopus represent a numerically important part of the passerine migration recorded on the Calf. The volume of Willow Warbler and Chiffchaff passage recorded is much greater in spring than in autiunn. Arrivals by Phylloscopus warblers on the Calf in spring coincide with calm, settled conditions and winds coming from the sector between south-west and south-east, while autumn passage totals show a broad similarity to the trends of the national Common Bird Census during the period. Interspecific differences in spring passage reflect differences in the breeding distribution of the two species in the British Isles. There also appear to be gender-related differences in the tinting of passage for both Chiffchaff and Willow Warbler.
McCanch, N.V. 2000. The relationship between Red-Billed Chough Pyrrhocorax pyrrhocorax (L) breeding populations and grazing pressure on the Calf of Man. Bird Study 47:295-303.
McCanch, N.V. 2000. A formula for determining age in nestling Shags Phalacrocorax aristotelis. Ringing & Migration 20:191-192.
McCanch, N.V. 1998. Skull ossification in a Chough. Ringing & Migration 19:79.
McCanch, N.V. 1998. Swallow with unmoulted greater coverts in spring. Ringing & Migration 19:30.
McCanch, N.V. 1997. Sparrowhawk passage through the Calf of Man 1959-93. Ringing & Migration 18:1-13.
McCanch, N.V. 1995. Willow Warbler with ant’s head attached to tarsus. British Birds 88:487.