12,000

We have over 12,000 students, from over 100 countries, within one of the safest campuses in the UK

93%

93% of Lancaster students go into work or further study within six months of graduating

Home > Research > Publications & Outputs > Factors influencing overnight loss of body mass...
View graph of relations

« Back

Factors influencing overnight loss of body mass in the communal roosts of a social bird

Research output: Contribution to journalJournal article

Published

Journal publication date04/2009
JournalFunctional Ecology
Journal number2
Volume23
Number of pages6
Pages367-372
Original languageEnglish

Abstract

1. Communal roosting behaviour in birds is hypothesized to reduce the risk of starvation by lowering the energetic expenditure required to survive the night. However, the metabolic benefit gained is likely to depend on various factors, including an individual's position within the roost.

2. The long-tailed tit Aegithalos caudatus L. is a social species that lives in flocks during the non-breeding season, forming linear roosting huddles in which individuals compete to avoid occupying the peripheral positions at either end of the roost. Using observations of 18 temporarily captive flocks of long-tailed tits, we examine the effects of position and other factors on the mass lost during roosting.

3. We found that, on average, long-tailed tits lost about 9% of their body mass overnight, and that individuals occupying the peripheral positions in a roost lost significantly more mass than those occupying inner positions.

4. Overnight mass loss was related to minimum temperature, being greatest at 4 degrees C and decreasing at higher and lower temperatures. This result suggests that long-tailed tits may use facultative nocturnal hypothermia to reduce energetic costs at low ambient temperature. Mass loss also tended to increase with group size, perhaps because of the greater competition for inner positions in larger flocks, although we have no direct evidence for this. Mass loss was also positively correlated with mass when going to roost, and males lost marginally more mass than females.

5. There was no evidence that individuals strategically adjusted their daily mass when going to roost in relation to their likely roosting position even though outer positions are consistently and therefore predictably occupied by the same individuals on successive nights.

6. We conclude that long-tailed tits mitigate the costs of surviving the night by roosting communally, but the benefits gained vary in relation to position within the roost, explaining previous observations of competitive interactions during roost formation.

7. The benefit derived from communal behaviour is likely to vary among individuals and the degree of conflict over these benefits is likely to depend on both intrinsic and extrinsic factors.