Popko Wiersma

Birds sacrifice oxidative protection for reproduction.

Oxidative metabolism has reactive oxygen species (ROS) as unavoidable by–products, and the damage ROS inflicts on DNA, proteins and lipids is considered to be a major agent of senescence. Increasing reproductive effort accelerates senescence, but whether reproductive effort is increased at the expense of protection against oxidative damage has not yet been tested. We manipulated reproductive effort in zebra finches through brood size manipulation and measured the activity of two major antioxidant enzymes (superoxide dismutase (SOD) and glutathione peroxidase (GPx)) in the pectoral muscle after 19–20 days of brood rearing. Oxidative stress is reflected by the balance between oxidative protection and ROS exposure, and we therefore scaled SOD and GPx activity to daily energy expenditure (DEE) as an index of ROS production. SOD and GPx activity decreased with increasing brood size by 28% and 24%, respectively. This effect was identical in the two sexes, but arose in different ways: males did not change their DEE, but had lower absolute enzyme activity, and females increased their DEE, but did not change absolute enzyme activity. This result suggests that senescence acceleration by increased reproductive effort is at least in part mediated by oxidative stress.

Scale and intensity of intertidal habitat use by knots Calidris canutus in the Western Wadden Sea in relation to food, friends and foes

Abstract In August–October 1988–1992 we studied the distribution and abundance of knots Calidris canutus around Griend in the western Wadden Sea, and the extent to which these can be explained by benthic prey availability and presence of avian predators. Numbers in the nonbreeding season showed monthly averages of 10 000 to 25 000 birds. Over 100 000 knots were recorded on three occassions. Knots feed in large flocks, individual birds usually experiencing 4 000 to 15 000 flock-mates. The Siberian-breeding/west-African wintering canutus subspecies passed through in late July and early August. Otherwise the Greenlandic/Canadian breeding islandica subspecies was present. Over the period 1964–1992 there were no clear trends in the number of knots, but canutus -knots were particularly abundant in July–August 1991, whereas in 1992 both subspecies were absent. Macoma balthica was the preferred prey of both subspecies. Hydrobia ulvae, Mytilus edulis and Cerastoderma edule were eaten when Macoma was absent close to the surface of the sediment. As Macoma buried deeper from July onwards, canutus faced better average feeding conditions than islandica later in the year. The spatial distributon of knots feeding on the intertidal flats around Griend was best explained by the harvestable biomass of the prevalent prey species in a particular year and season, i.e. Macoma (main prey when their harvestable biomass densities were greater than ca 0.8 g AFDM per m 2 ) and Cerastoderma , and by the avoidance of situations where they run the risk of attack by bird-eating birds. Flocks of knots covered most of the intertidal flats in the Western Dutch Wadden Sea in a couple of tidal cycles. This is about 800 km 2 , much larger than the equivalent area used by knots on their wintering grounds in Mauritania (10–15 km 2 ), a difference that is correlated with prey spectrum, prey availability and predictability.

Comparison of the cost of short flights in a nectarivorous and a non-nectarivorous bird

SUMMARY Although most birds are accustomed to making short flights, particularly during foraging, the flight patterns during these short periods of activity differ between species. Nectarivorous birds, in particular, often spend time hovering, while non-nectarivorous birds do not. The cost of short flights is likely therefore to differ between nectarivorous and non-nectarivorous birds because of the different energetic contributions of different flight types to the behaviour. The 13C-labelled bicarbonate technique was used to measure the energy cost of short flights in the nectarivorous Palestine sunbird Nectarinia osea (mean mass 6.17±0.16 g, N=8) and the non-nectarivorous starling Sturnus vulgaris (mean mass 70.11±1.11 g, N=9). The technique was initially calibrated in five individuals for each species at temperatures ranging from 1 to 35°C, by comparing the isotope elimination rate to the metabolic rate measured simultaneously by indirect calorimetry. The cost for short intermittent flight was then measured by encouraging birds to fly between two perches at either end of a narrow corridor (perch distance for sunbirds, 6 m; for starlings, 5 m), and measuring the amount of isotope eliminated during the flight. The isotope elimination rate was interpolated onto the calibration equation to predict flight cost, as a direct calibration could not be performed during flight. Mean energy expenditure during flight was 1.64±0.32 W in sunbirds, while in starlings the flight costs averaged 20.6±0.78 W. Energy cost of flight relative to basal metabolic rate was substantially greater in the starling than the sunbird. Phylogenetic analysis of different modes of flight in these and additional species suggests that differences in flight behaviour may cause these elevated costs in slow flying non-nectarivores such as starlings, compared to birds that are more prone to short intermittent flights like the sunbirds.

Social foraging by waterbirds in shallow coastal lagoons in Ghana

Abstract Social foraging in waterbirds in Ghanaian coastal lagoons was studied during October and November 1994. Two types of foraging were social: directionally synchronized flocks (often involving distinctive feeding methods used in unison) and dense pecking aggregations. Social flocks were typically larger and denser than non-social flocks, and primarily involved piscivorous birds, especially the longer-legged shorebirds and egrets. It is probable that the flocks concentrate fish into temporarily high densities through herding or confusing escape reactions. We suggest that these flocks, rather than simply forming in areas of existing high prey density, may actively enhance their foraging success. There may be a true social element to either the initiation or persistence of waterbird social foraging flocks in coastal Ghana.

Climate Change and Advanced Primary Moult in Eurasian Golden Plovers Pluvialis apricaria

We measured primary moult scores of 1051 Eurasian Golden Plovers Pluvialis apricaria staging in pastures in The Netherlands from 1978 to 2011. We hypothesized that moult may have advanced due to earlier breeding resulting from global climate change. At the same time, intensification of agricultural practices has changed the environment on which the Golden Plovers depend during migration and staging, which may have affected their condition and moult schedule. Primary moult has advanced by 8 days from 1990 to 2011, without visible changes preceding 1990. This suggests that long-term changes in weather might have caused the change in moult timing. In the absence of the variable year, the North Atlantic Oscillating (NAO) index, averaged over September–October, significantly correlated with timing of moult. However, this was a weaker relationship than that of year and timing of moult. Apparently, year correlates better with relevant weather parameters than NAO. Because moult speed at the staging areas has not changed from 1978 to 2011, the birds must have started moult earlier. Advanced breeding has been shown to have occurred in several bird species breeding in northern temperate latitudes. Golden Plovers start to moult during breeding, and therefore we think that the advancement of moult has been the result of an earlier start of breeding and not of changes in agricultural practice in The Netherlands.