A study of treecreepers

Abstract

The data available from die extensive studies of B.T.O. members have been com- bined and compared for analytical purposes with data from an intensive study of the Treecreeper in deciduous woodland in North Kent First eggs are usually laid in early April, with peak laying in late April and early May. While the majority of birds are single-brooded, a proportion of second broods are recorded each year, apparently associated mainly with coniferous woodland, possibly reflecting on the apparently anomalous situation of the Treecreeper in Britain by implying a greater affinity for conifers-which is the situation for C. familiaris in Continental Europe. The mean clutch size is about five eggs, and losses during incubation appear to be small. Methods of investigating success and productivity, and the causes of failure, are discussed. The mean incubation period was found to be 14.5 days, and the mean fledging period 15.1 days. Ringing recoveries allow little useful analysis, but there are some indications from retrtap data that calculations based on dead birds alone may result in appreciable underestimates of life span. Weight fluctuates very little during the year, the overall means calculated for the twelve months ranging from 8.8 to 9.5 gm. Standard deviations are small, and there is no apparently regional variation. The minimum weight reported was 7.1 gm, the maximum 13.75 gm. While there is evidence to suggest a sexual dimorphism in wing length, the difference is too small to be of practical field value in extensive surveys. The pattern of moult is broadly similar to that of the Blue Ht and Great Tit: primaries begin to fall in the second half of June, finishing on average about 75 days later. Body and head moult continue for a further two or three weeks, and the total moult may occupy up to 100 days. Tail moult is uncharacteristic of passerine birds: the outer feathers are moulted separately from the centre pair, and as in the woodpeckers, the Treecreeper retains throughout the moult the 'prop' function of its tail. © Taylor & Francis Group, LLC.