Iain Taylor

THE USE OF IR THERMOGRAPHY TO MEASURE THE RADIATIVE TEMPERATURE AND HEAT LOSS OF A BARN OWL (TYTO ALBA)

Abstract Infrared (IR) thermography was used to identify the major sites of heat loss from a female barn owl at an air temperature of 17.6°C. When perched, the mean radiative temperature of the owl was 21.1°C (SD=3.5). The facial disc averaged 23.9°C (SD=9.1) and the temperature of the eyes was greater than 33°C. Images showed an area on the lower abdomen that was warmer than 27°C. During flight, the temperature of plumage overlying wing muscles was more than 30°C. The metabolic heat production of the barn owl was estimated to be 42 W m−2 (1.68 W) at 17.6°C which agreed with previous measurements of metabolism. Heat loss from the head was almost double that from the body as a whole, indicating the importance of reducing exposure of the head during roosting. The metabolic rate during flight was calculated to be 13×BMR ( Pennycuick, 1989 ). This suggested that barn owls lose considerable amounts of heat during prolonged periods of flight. It is hypothesised that by being active in cool nocturnal conditions, barn owls may exploit waste metabolic heat for thermoregulation.

Are Rice Fields in Southeastern Australia an Adequate Substitute for Natural Wetlands as Foraging Areas for Egrets

Abstract Within the Murray-Darling Basin of eastern Australia there has been a general decline in the abundance of wading birds. Loss of wetlands caused by river regulation and irrigated agriculture is considered to be the main cause. We assessed the adequacy of irrigated rice fields as substitutes for natural wetlands for foraging egrets during the breeding season in one study area around a mixed colony of egrets in southeast Australia. For aerially sown rice crops, which represented 85% of all rice in the general area, the densities of foraging Intermediate Egret (Egretta intermedia) and Great Egret (Ardea alba) tended to reach a maximum four to six weeks after sowing of the rice crop, and declined thereafter. The decline phase was correlated with decreasing prey capture rates and a shift from vertebrate prey to less profitable invertebrate prey, and coincided with the start of the egrets’ main chick rearing period when food demands would have been high. Even at maximum densities it was estimated that only 5-13% of the Intermediate Egrets and Great Egrets that were available to feed actually did so in the rice growing areas within 6.5 km of the colony. In contrast, Cattle Egret (Bubulcus ibis) densities in rice fields did not decline until after their young fledged. They fed almost exclusively on insects and their prey capture rates showed no seasonal decrease. Up to 60% of the available Cattle Egrets were found feeding in the rice fields within 6.5 km of the colony. It is concluded that rice fields provide a good foraging habitat for the Cattle Egret and may be contributing to the spread of this invasive species, but that they are probably not a preferred foraging habitat for the Intermediate Egret and the Great Egret.

The Foraging Ecology of Egrets in Rice Fields in Southern New South Wales, Australia

-Numbers of wading birds are declining throughout the Murray-Darling Basin in Australia, and the loss of wetland habitats to agriculture is the most likely cause. This study describes the foraging of egrets in irrigated rice fields that occur extensively in areas of former wetlands. Tadpoles were the main prey of Great and Intermediate Egrets (Ardea alba and A. intermedia), with insects important secondary prey. Insects were the main prey of Cattle Egrets (A. ibis). Prey capture rates for Great and Intermediate Egrets declined by around 40% between November and January as the rice plants grew from seedling to mature stages. Cattle Egret prey capture rates did not decline. The abundance of tadpoles and most aquatic insects in the rice fields declined significantly between November and February. All three egret species laid eggs mainly during December and had young in the nest duringJanuary and February. Thus the declining profitability of rice fields as foraging sites coincided with the maximum demand for food by the birds to rear their young. Rice fields may not be an adequate substitute for natural wetlands for Great and Intermediate Egrets. Received 14 February 2001, accepted 20 March 2001.

The ecology of sewage treatment gradients in relation to their use by waterbirds

The distribution and abundance of waterbirds along sewage treatment gradients at the Western Treatment Plant (Victoria, Australia) were studied in late summer/early autumn 2000. In general, the highest densities and diversity of waterbirds, and of zooplankton, were found in the ponds towards the end of a treatment series. Filter-feeding waterfowl (Anatidae) probably used these ponds because of the availability of zooplankton as a food-source. Dissolved oxygen concentration generally increased along the treatment gradient and un-ionised sulphide concentration decreased, and it is possible that either one, or both, of these played a key role in determining the distribution of zooplankton.

Long-term trends in the abundance of breeding Lapwing Vanellus vanellus in relation to land-use change on upland farmland in southern Scotland

Capsule A long-term decline on this habitat is shown to be associated with the intensification of agricultural management, particularly the occurrence of field drainage. Aims To assess long-term trends in the number of breeding Lapwing and determine the relationship between these trends and changes in agricultural management on an upland study area. Methods Breeding Lapwing were counted along two road transects in nine years between 1980 and 2002, and on one extensive plot in 1980, 1990 and 2000. Counts along the road transects were made from a vehicle and the fields used for nesting were recorded. Changes in field management along the transects were monitored annually between 1980 and 1990, and habitat composition assessed in 1980, 1985, 1990 and 2000. Results During the first 20 years of study the number of breeding Lapwing declined substantially on all three count areas and by 77% overall, with further declines on both transects in 2002. The area of unimproved grassland and arable on these transects also declined substantially due to conversion to improved grass. Fields that comprised either unimproved grassland or arable were most likely to hold nesting Lapwing, while the chance of a field losing its nesting Lapwing was positively associated with the occurrence of drainage. Drainage and conversion to improved grass were closely linked. Conclusions Agricultural intensification is a probable cause of decline in the number of breeding Lapwing in upland areas. Such declines may have been widespread in upland areas following increased agricultural intensification in recent decades.

Activity budgets of waterfowl (Anatidae) on a waste-stabilisation pond

Abstract This study investigated the activity budgets of eight species of waterfowl on a waste-stabilisation pond known to support a large waterfowl community. Most species examined were found to use the area extensively for feeding. Pink-eared Duck (Malacorhynchus membranaceus), Australasian Shoveler (Anas rhynchotis), Grey Teal (A. gibberifrons) and Chestnut Teal (A. castanea) fed most intensively at sunrise and sunset, and rested during the middle of the day. Hardhead (Aythya australis), a diving species, Australian Shelduck (Tadorna tadornoides) and Pacific Black Duck (Anas superciliosa)—large birds that were presumably able to reach the benthos from the waters surface—fed at relatively consistent levels throughout the day. Black Swans (Cygnus atratus) steadily increased the amount of time spent feeding from dawn to dusk. The diurnal activity budgets of these Australian species were similar to those observed for other species occupying similar ecological niches elsewhere. Imminent changes to sewage treatment operations may reduce the ability of this waste-stabilisation pond to support waterfowl populations. The monitoring of activity budgets after any such changes are implemented should be an effective means of detecting any effects, negative or positive.

Waterbird use of Rice Fields in Australia

Abstract. Rice (Oryza sativa) growing in Australia occurs almost exclusively in the south-east, in the Riverine Plains of the Murray-Darling Basin, with an annual average of 110,000 ha. All crops are grown under irrigation using water abstracted from rivers. Rice fields are flooded between October and March and are dry otherwise. A large decrease in natural wetland extent and declines in most waterbird populations have been associated with the increase in irrigated agriculture since the 1960s. The ecology of waterbirds in rice fields has been studied in only one area, around Fivebough Swamp in southern New South Wales. Thirty-seven waterbird species were recorded in rice fields compared with 70 species on an adjacent natural wetland. Species diversity and the abundance of individual species declined as the rice crops developed so that most species used rice fields for only one to two months after flooding. An increase in water depths associated with the timing of panicle initiation of the rice plants was probably the main cause, but declines in most waterbird prey species also occurred as the crops developed. Rice crops were particularly important feeding areas for Glossy Ibis (Plegadis falcinellus) during November and December. Small numbers of the threatened Australasian Bittern (Botauins poiciloptilus) were also recorded.

Winter microclimate of field voles (Microtus agrestis) in SW Scotland

The microclimate of the field vole (Microtus agrestis) was measured in rough grassland in SW Scotland from February–April 1992. Measurements represented conditions experienced by voles when foraging. Air temperature in the grass tunnels used by voles was only 0.3°C greater than air temperature above the vegetation. On average, the change in temperature in grass tunnels and at feeding stations used by voles matched the diurnal increase in air temperature. However, snow cover was found to insulate vole habitat from large changes in air temperature. The grassland provided considerable shading from solar radiation and shelter from wind. Solar radiation and wind speed at the surface were closely coupled with conditions above the ground surface due to the short height of grassland at this season of the year. Although the winter temperatures experienced by field voles are well below their thermoneutral zone of metabolism, their sheltered microclimate means that they can remain active in wet and windy weather when predators may be less able to detect them.

The effect of wind speed and wetting on thermal resistance of the barn owl (Tyto alba). II: Coat resistance

Abstract 1. 1. The thermal resistance of barn owl (Tyto alba) plumage was determined from measurements of heat flux and temperature using a model in a wind tunnel. 2. 2. The mean resistance of four barn owl coats was 398 s m−1 and wetting the coat reduced coat resistance to 374 s m−1. Resistance decreased linearly with increasing wind speed from 0–7 m s−1. 3. 3. Half of the heat transfer within barn owl coats occurred by conduction through the feather elements, the remaining heat transfer was due to molecular diffusion of air within the coat (30%), radiation (10%) and free convection (10%). 4. 4. Thermal properties of barn owl plumage were comparable with previous findings on avian coats.

THE EFFECT OF WIND SPEED AND WETTING ON THERMAL RESISTANCE OF THE BARN OWL(TYTO ALBA). I : TOTAL HEAT LOSS, BOUNDARY LAYER AND TOTAL RESISTANCE

Abstract 1. 1. The sensible heat loss and thermal resistance of a barn owl ( Tyto alba ) were determined using a heat transfer model in a wind tunnel. 2. 2. Heat loss was a linear function of wind speed and increased by 60% between 0 and 7 m s −1 . Wetting the model increased heat loss by 30%. 3. 3. Boundary layer resistance of the model decreased from 223 s m −1 in still air to 56 s m −1 at a wind speed of 1.3 m s −1 and remained constant at wind speeds up to 7 m s −1 . 4. 4. The relationship between Nusselt and Reynolds numbers for the model was linear, as was the relationship for cylinders over the range in Reynolds numbers. Nusselt numbers for the plumage-covered model were, however, 30% lower than those derived for the uncovered model. 5. 5. Total thermal resistance of the model was 508 s m −1 (dry) and 486 s m −1 (wet), decreasing by almost 60% from 0 to 7 m s −1 . There was a nonlinear decrease in total resistance with increasing wind speed, mainly due to the change in boundary resistance between 0 and 1.3 m s −1 .