Body-Mass Variation in Breeding Northern Wheatears: A Field Experiment with Supplementary Food

Abstract

Changes in body mass of breeding Northern Wheatears, Oenanthe oenanthe, on the island of Oland, south Sweden, were monitored during 1985-1987 in the context of a food provisioning experiment. Individuals were weighed periodically by attracting them to feeders which were placed on electronic digital balances. Rations of 7 g of mealworms per visiting individual were offered daily on certain territories (in 1987, some individuals were offered rations of 4.5 and 9 g). Unprovisioned birds were captured and weighed during the study. Males maintained constant body masses throughout the season. Females increased in mass up to laying, maintained relatively large masses during incubation, and dropped in mass by 14% during the first week after the young hatched. Mass then attained constant levels until the time ofoffspring independence. There was a positive correlation between brood size and the masses of unprovisioned females during the late nestling phase. Extra food had a positive effect on the general mass level of females but not of males. However, provisioning had no significant effect on the masses of females feeding thermoregulating nestlings, indicating that reproductive stress is not important in determining posthatching mass losses. All females lost mass after hatching, and the heaviest lost proportionally more. Extra food was delivered almost exclusively to the chicks a few days after hatching. Females apparently maintain reserves during incubation and transfer them to the young after hatching by a voluntary shift in the allocation of collected food. Males do not store reserves and have therefore no scope for significant mass changes.

Spring arrival along a migratory divide of sympatric blackcaps (Sylvia atricapilla)

“…The condition of blackcaps upon arrival was assessed using body mass and two additional morphological indices as indicators: body mass divided by tarsus length (Matthysen 1989;Moreno 1989), and the residuals of the body mass 9 tarsus regression (2006, F 1,104 = 19.83, R 2 = 0.160, P \ 0.001; 2007, F 1,107 = 4.13, R 2 = 0.04, P \ 0.05). Residuals from the regression, that is observed minus fitted values, were taken as a proxy for body condition (Bize et al 2006;Hochachka and Smith 1991).…”

Variation in body condition of breeding Savi’s Warblers Locustella luscinioides: the reproductive stress and flight adaptation hypothesis revisited

“…Moreno 1989b;Hillström 1995), or manipulating brood size (Nur 1984;Moreno and Carlson 1989;Merilä and Wiggins 1997), incubation (Cichoń 2000) or brooding periods (Sanz and Moreno 1995). Most of the food supplementation and brood manipulation experiments reached the conclusion that the weight change is adaptive (Moreno 1989b;Sanz and Moreno 1995;Merkle and Barclay 1996;Cavitt and Thompson 1997;Slagsvold and Johansen 1998), but there are exceptions (Cucco and Malacarne 1997;Nagy et al 2007). Correlation studies often assume (for passerines) that the most energetically demanding period of the breeding cycle is the second half of the nestling period (when nestlings demand a greater feeding rate).…”

Usefulness of Biometrics to Analyse Some Ecological Features of Birds

“…b) When we do not wish to capture the bird, attracting it to a place situated on a scale which automatically records mass variation will suffice. This procedure has been employed, for example, to analyze body mass variation in breeding birds when they regularly visit the nest (Moreno, 1989;Szép et al, 1995), and amount of food brought to the nestlings (Reid et al, 1999), etc. Two important issues should be taken into account in the data analysis: body mass variation with time of day and pseudoreplication of data which could distort the conclusions obtained (see review by Rands et al, 2006).…”