BRANTA — Chris Pendlebury
Variation in energetic costs during laying in birds: effects on eggs and laying patterns
Institution: University of Stirling, U.K.
Supervisors: DM Bryant, IJ Stevenson, M MacLeod
Details: PhD 2003 (Completed)
Address: BTO Scotland, SBES, Stirling University, Stirling, UK, FK9 4LA (Nov 2005) Email
Subject Keywords: Birds, eggs, energetics, DLW, temperature, food supply
Species Keywords: Great Tit Parus major, Japanese Quail Coturnix japonica
The main aim of this project was to investigate how two key environmental factors, temperature and food supply, affected investment in egg production. In addition, the way investments might change under different climate change scenarios was considered.
Fieldwork was carried out on great tits (Parus major) to test experimentally some predictions concerning constraints imposed on laying birds by thermoregulatory and foraging costs. This involved manipulating overnight nestbox temperatures of laying birds, and a supplementary-feeding experiment. The effects of the treatments on egg production and daily energy expenditure (DEE) were then studied. DEE was measured using the doubly-labelled water technique. Both manipulations affected egg mass. Temperature manipulations also affected energy expenditures and the frequency of laying interruptions.
The effects of temperature variation on energy expenditure, using respirometry, and egg production were investigated in Japanese quail (Coturnix japonica). An increase in daily temperature variation, and a sudden change in temperature, both resulted in higher energy expenditures and smaller eggs being produced, than under contrasting conditions at the same mean temperature. Temperature variation, as well as mean temperature, therefore needs to be considered when investing the effects of temperature on wild animals. Wild great tits showed similar responses, with smaller eggs being laid when temperatures during the week prior to laying were more variable.
This thesis shows that energy budgets are particularly important for laying birds. Energetic constraints can be imposed at low temperatures and low levels of food supply, which can affect resource availability for egg production, and consequently affect the onset of laying. Energetic constraints are likely to override those imposed by any rare nutrients required for eggs, particularly at low temperatures. The effects of temperature are likely to be greater for smaller birds due to their generally higher thermoregulatory costs.
The constraints detected may impact on laying birds by preventing them from breeding at the most favourable time. A lessening of these constraints must occur if laying dates are to advance as a result of climate warming. This may not occur if temperatures do not increase equally throughout the breeding season. Hence, if food supplies are advanced but constraints on laying persist, then mis-matching of reproduction and resource availability may occur.
Pendlebury, C.J. & Bryant, D.M. 2005. Effects of temperature variability on egg mass and clutch size in great tits. Condor 107: 710-714.
Pendlebury, C.J. & Bryant, D.M. 2005. Night-time behaviour of egg-laying tits. Ibis 147: 342-345.
Pendlebury, C.J., MacLeod, M. & Bryant, D.M. 2004. Variation in temperature increases the cost of living in birds. Journal of Experimental Biology. 207: 2065-2070.