Breeding ecology and oviposition site selection of black-spotted pond frogs (Rana nigromaculata) in Ningbo, China

The black-spotted pond frog (Rana nigromacu-lata) is one of the most widely distributed species in China. However, there have been only a few qualitative descrip-tions of their breeding ecology and oviposition site selec-tion. From 2004 to 2006, we investigated the breeding ecology and oviposition site selection of K nigromaculata in Ningbo, China, quantitatively. Analyses of breeding ecology show that: (1) mean frog density in the breeding season was 0.0903 ± 0.0029 individuals per meter (n = 11) (mean ± SE); (2) R. nigromaculata was a sexually dimorphic species, with females significantly larger than males in both body weight and snout-vent length; (3) the clutch size averaged 4643.04± 235.96 eggs (range 1546-7897, n = 50); and (4) the egg size ranged from 1.50 to 1.74 mm in diameter, with an average egg size of 1.6050 ± 0.0046 mm (n = 226). Oviposition sites differed significantly from random sites in percentages of water, bare ground and vegetation cover, water depth (cm), water temperature (°C) and water turbidity. Rana nigro-maculata preferred microhabitats with higher percentages of water and vegetation cover, while it avoided microha-bitats with deeper water. The results suggest that micro-habitats with higher percentages of water and vegetation cover, but not deeper water, should be priorities for pro-tection and conservation of the breeding habitats of R. nigromaculata.     

Aspects of breeding ecology of the eastern olivaceous warbler (Hippolais pallida)

The breeding ecology of eastern olivaceous warblers Hippolais pallida is poorly known. In this study, we provide data on nest site selection and breeding parameters of the species in a population in northwestern Bulgaria, the only one known to be regularly and heavily parasitized by the common cuckoo Cuculus canorus (hereafter cuckoo). Eastern olivaceous warblers only bred within human settlements of the study area, avoiding seemingly suitable habitat outside them. Nests were built in a wide range of plant taxa but ailanthuses Ailanthus altissima and mulberries Morus spp. were most frequently used (21%). After taking into account the availability of vegetation, there was an apparent preference for several plant taxa but not for mulberries. Mean nest height was 1.65 ± 0.98 (0.53–7.60) m, n = 217, and it varied significantly among different types of nesting substrate. Laying date and clutch size of first breeding attempts averaged 10 June ± 0.98 days, n = 101 and 3.9 ± 0.07 (2–5) eggs, n = 72, respectively. Hatching success, fledging success, and breeding success were 42.5, 86.4, and 36.7%, respectively. The main sources of nest mortality were predation and cuckoo parasitism, with no significant difference in the proportion of nests lost to each. Cuckoo parasitism seemed responsible for the relatively low hatching success in this population.     

Breeding biology of Montagu’s Harrier Circus pygargus in north-central Kazakhstan

The ecology and conservation status of Central Asian populations of Montagu’s Harriers Circus pygargus are poorly known. We studied the breeding biology of this species during 3 years in the Naurzum region, north-central Kazakhstan. Most Montagu’s Harriers in the study area nested in the forest-steppe transition area, in bushy areas dominated by dogrose Rosa canina, which was apparently the nesting vegetation type providing highest and densest nest cover in the study area. Laying occurred from 26 April to 7 June (average 13 May, n = 49) and, although it varied significantly between years, was earlier than in western European populations of similar latitude. Mean (±SD) clutch size was 4.44 ± 0.86 (range 2–6; n = 50), in the higher range observed for the species. There was no significant interannual variation in clutch size, despite large variations in the abundance of small mammals in the area. Diet was mainly composed of lizards (54.2%, n = 533 identified prey in all 3 years), with small mammals (17.1%), passerine birds (14.3%) and insects (13.6%) also being consumed. Mean brood size at the last visit was 2.55 ± 2.10 (range 0–6; n = 51). Failure rate was relatively high; the main identified cause of nest failure was predation. We compare the data obtained in this population breeding in natural steppes with breeding parameters from the well-studied western European populations, and discuss the implications for the conservation of this species.     

Space use and habitat preferences of the invasive American mink (<Emphasis Type="Italic">Mustela vison</Emphasis>) in a Mediterranean area

Space use, intra-territorial habitat preferences, and factors affecting both were studied in an invading population of American mink, Mustela vison, in two rivers of a Mediterranean region of Spain. Average linear home range was 1.19 ± 0.73 km (±SD) and core area was 0.21 ± 0.08 km for resident males (n = 10); while for females (n = 5) they were 0.54 ± 0.14 and 0.19 ± 0.11 km, respectively. Overlapping between the home ranges of residents was low. In no case their core areas overlapped. Home ranges were small in comparison to other study areas and in general the resident minks were territorial. Linear home range length was related to individual weight and to the river. Weight had a positive effect indicating a potential body condition effect, while river may be showing a habitat quality effect. Habitat preferences were positively affected by the abundance of helophytic vegetation and negatively by the presence of human activity. Helophytic vegetation offers both food and refuges, while human activity may represent a potential danger. Percentage of captures was higher inside the core areas and was slightly influenced positively by abundance of helophytic vegetation. All this information should be considered when designing and implementing measures to control the expansion of American minks. We recommend keeping going with the trapping sessions but, given the results obtained, reducing the distance between traps down to 200 m to maximize capturability (i.e., about doubling the trapping effort), and, when available, placing them near helophytic vegetation. In the absence of helophytic vegetation, traps should be located near any kind of vegetation providing coverage for mink and far from human activity.     

Predation of frog eggs by the water strider Gerris latiabdominis Miyamoto (Hemiptera: Gerridae)

Water striders (Hemiptera: Gerridae) are predators found on the water surface that prey mainly on arthropods. The feeding on other organisms (dead vertebrates, fishes and tadpoles) is a rare event. To our knowledge, predation of frog eggs by water striders has not yet been reported. We observed that adult water striders, Gerris latiabdominis Miyamoto, 1958 (Hemiptera: Gerridae), preyed on the eggs of three frog species, Pelophylax nigromaculata Hallowell, 1861 (Anura: Ranidae), Rana japonica Boulenger, 1879 (Anura: Ranidae), and Rhacophorus schlegelii Günther, 1858 (Anura: Rhacophoridae). We found predation by the water striders affects the survival rate of frog eggs floating on the water surface. We suggest that this hunting event would occur in water bodies in which water striders and frogs coexist, especially the region where their phenology overlaps.     

Timing of breeding, habitat preference and reproductive success of marsh harriers (Circus aeruginosus)

During 2002–2005 we analyzed Lack’s Hypothesis about the timing of the breeding of marsh harriers (Circus aeruginosus) in the Poodří to the breeding period and preference of heterogeneous habitat. An analysis of 43 nests revealed quantitative differences. Birds which started breeding earlier, reached significantly higher reproductive success than later breeding birds regardless of nesting habitat (P = 0.003, n _nests = 43). Even when the birds invested into their offspring the same way, their breeding success was not always the same. When the females nested in the common reed (Phragmites communis), they reached higher reproductive output than females nesting in cattail (Typha sp.) (P = 0.01, n _cattail = 18, n _{common reed} = 25). The habitat of the common reed is characterized by higher and denser vegetation cover than cattail vegetation (P < 0.001, n _measurements = 174 for both variables).     

The western jewel butterfly (Hypochrysops halyaetus: Lycaenidae) II: factors affecting oviposition within native Banksia bushland in an urban setting

Oviposition by western jewel butterflies (Hypochrysops halyaetus Hewitson) was studied in the urban Koondoola regional bushland reserve, Western Australia in 1999. Observations were made in a small (70 × 120 m) localised breeding area the ‘microdistribution study area’, and in 14 paired 20 × 20 m quadrats randomly placed along established tracks in the interior of the northern half of the reserve. The principal host plant was Jacksonia sternbergiana with the secondary host being Daviesia divaricata. More Jacksonia were used for oviposition and attended by ants (40 and 71%, respectively) in the microdistribution study than plants in the ‘quadrat’ study (8 and 25%, respectively). Jacksonia stems with basal diameters below 5 mm were less likely to have eggs. PCA showed Jacksonia to be associated with disturbed conditions with a high proportion of bare ground whereas Daviesia was associated with more mature vegetation. Jacksonia density was principally correlated with the proportion of bare ground and time since the last fire. Host ant (Crematogaster perthensis) presence and proportion of bare ground were the most important factors influencing oviposition. The presence of ants was closely associated with bare ground conditions and the presence of coccids. Conservation management for floristic diversity and maturity of vegetation in reserves is likely to be a widespread phenomenon, and may negatively affect the persistence of species requiring ephemeral patches of early successional vegetation. For H. halyaetus, a species dependent on disturbed/ephemeral habitat conditions, this conflict may threaten its survival, especially in small reserves, and as a result its conservation status may be underestimated. Management options are discussed.     

Effect of photoperiod and temperature on ovarian cycle of the frogRana tigrina (Daud.)

The effect of varying photoperiod regimes (LD: 20,4; 4,20; 6,18; 18,6 and 12,12) on ovarian follicular development was analysed in the frogRana tigrina maintained at ambient and constant 30° ± l°C for 3 months. The experiments were conducted in early recrudescent and quiescent phases. The frogs were fed guppiesad libitum on alternate day. None of the photoperiod regimes had any effect on the ovaries or the fat bodies, whereas exposure to constant high temperature (regardless of photoperiod) during recrudescent phase induced production of greater number of eggs (∼ 18000 vs 13000 in controls) of ovulatory sizes (> 1400 μm) compared to the corresponding controls maintained at ambient temperature. Hence, ovarian mass also increased in these frogs. In the quiescent phase, high temperature merely enhanced growth of previtellogenic oocytes. In both the phases high temperature caused a reduction in the fat bodies over the respective controls, possibly due to increased metabolic activity. The above findings indicate that temperature plays a key role in the regulation of ovarian cycle ofRana tigrina and that the photoperiodic mechanisms may not govern the annual recrudescence of ovaries in the frog. The study also shows that the frog exhibits the phenomenon of “phenotypic plasticity” in its reproductive behaviour by producing significantly greater number of eggs in response to elevated temperature.     

Survivorship,potential, and realized fecundity ofBiosteres tryoni [Hymenoptera: Braconidae], a larval parasitoid ofCeratitis capitata [Diptera: Tephritidae]

Laboratory-rearedBiosteres tryoni (Cameron) reached peak ovarian maturation on the 5^th and 7^th days after emergence in unmated and mated ♀♀, respectively. When ♀♀ were not allowed to oviposit, contents of the oocytes were hydrolyzed and reabsorbed. However, when hosts were available for oviposition a significant increase of egg maturation rate was noticed. Mean realized fecundity during the life span was 71.7±8.1 and 69.0±6.7, and mean longevity was 13.5±0.9 and 15.1±0.6 days for mated and unmated ♀♀ respectively.      

<Emphasis Type="Italic">Fopius arisanus</Emphasis> oviposition in four <Emphasis Type="Italic">Anastrepha</Emphasis> fruit fly species of economic importance in Mexico

We studied the oviposition performance of Fopius arisanus (Sonan) (Hymenoptera: Braconidae) attacking eggs of four fruit flies of the genus Anastrepha Schiner (Diptera: Tephritidae) under laboratory conditions. The complete process of oviposition on an individual egg of Anastrepha ludens (Loew) lasts in average 85.4 ± 2.9 s, including a tremor (25.8 ± 1.03 s) observed in the middle of this process related to the egg’s descent. The average parasitism of A. ludens egg was 60.9 ± 7.5%, with only 1.2% of superparasitized eggs. During individual acts of oviposition, we noted that F. arisanus possesses a highly flexible ovipositor that curves easily as it searches for additional suitable eggs, which may be of particular benefit when a female finds large clutches of eggs. The individual oviposition of F. arisanus in host fruits attacked by Anastrepha spp. varies with the egg clutch size of each fruit fly species: A. serpentina laid the biggest egg clutches (21.3 ± 1.4), followed by A. ludens (14.2 ± 0.9), and A. striata (1.0 ± 0.0) (=A. obliqua). The time spent by F. arisanus in individual ovipositions was parallel to these findings, reinforcing the idea that F. arisanus attacks several eggs in each individual insertion of its ovipositor. Neither formal oviposition acts, nor adult emergences of F. arisanus were registered in A. obliqua. We discuss the potential of F. arisanus as natural enemy of fruit flies of the genus Anastrepha, and explore the eventual developing of its mass rearing. Handling Editor: Torsten Meiners.     

The choice of oviposition site and the effects of density and oviposition timing on survivorship in<Emphasis Type="Italic"> Rana japonica</Emphasis>

In species that lack parental care and whose larvae are restricted to a given space throughout development, choice of egg-laying or reproductive sites often greatly influences fitness. Furthermore, reproductive success of individuals may be affected not only by conditions of the breeding area but also by the time when they start to breed, because intraspecific variation in the timing of breeding may result in asymmetric competition between larvae. We addressed these issues in an experimental and field study of the Japanese brown frog, Rana japonica. We tested whether the survival success of larvae decreased with an increase in the number of deposited egg masses and with a greater delay in oviposition. We found that the number of egg masses and timing of oviposition together significantly predicted larval survival per clutch. Moreover, we observed the natural oviposition of R. japonica to examine the prediction that if the density of larvae and the timing of oviposition affect survivorship of larvae, R. japonica will avoid depositing eggs in pools in which egg masses have already been deposited. We found that for small pools only, R. japonica tended to favor oviposition at unoccupied pools (those lacking egg masses and larvae) in the spawning season. For large pools, however, adults favored those already occupied by egg masses in the spawning period. The density of egg masses and tadpoles or the timing of oviposition may have less effect on spawning or the survival of tadpoles in large pools than in small pools.     

Phenological delay despite warming in wood frog Rana sylvatica reproductive timing: a 20-year study

Across all taxa, amphibians exhibit some of the strongest phenological shifts in response to climate change. As climates warm, amphibians and other animals are expected to breed earlier in response to temperature cues. However, if species use fixed cues such as daylight, their breeding timing might remain fixed, potentially creating disconnects between their life history and environmental conditions. Wood frogs Rana sylvatica are a cold-adapted species that reproduce in early spring, immediately after breeding ponds are free of ice. We used long-term surveys of wood frog oviposition timing in 64 breeding ponds over 20 yr to show that, despite experiencing a warming of 0.29°C per decade in annual temperature, wood frog breeding phenology has shifted later by 2.8 d since 2000 (1.4 d per decade; 4.8 d per °C). This counterintuitive pattern is likely the result of changes in the timing of snowpack accumulation and melting. Finally, we used relationships between climate and oviposition between 2000 and 2018 to hindcast oviposition dates from climate records to model longer-term trends since 1980. Our study indicates that species can respond to fine-grained seasonal climate heterogeneity within years that is not apparent or counterintuitive when related to annual trends across years.     

Restoring ponds for amphibians: a success story

Large-scale restoration of quality habitats is often considered essential for the recovery of threatened pond-breeding amphibians but only a few successful cases are documented, so far. We describe a landscape-scale restoration project targeted at two declining species—the crested newt (Triturus cristatus Laur.) and the common spadefoot toad (Pelobates fuscus Wagler)—in six protected areas in southern and southeastern Estonia. The ponds were restored or created in clusters to (i) increase the density and number of breeding sites at local and landscape levels; (ii) provide adjacent ponds with differing depths, hydroperiods and littoral zones and (iii) restore an array of wetlands connected to appropriate terrestrial habitat. In only 3 years, where 22 of the 405 existing ponds (5%) were restored and 208 new ponds (51%) created, the number of ponds occupied by the common spadefoot toad increased 6.5 times. Concerning the crested newt and the moor frog (Rana arvalis Nilsson), the increase was 2.3 and 2.5 times, respectively. The target species had breeding attempts in most of the colonised ponds—even more frequently than common species. Also, the amphibian species richness was higher in the restored than in the untreated ponds. The crested newt preferably colonised ponds that had some submerged vegetation and were surrounded by forest or a mosaic of forest and open habitats. The common spadefoot toad favoured ponds having clear and transparent water. Our study reveals that habitat restoration for threatened pond-breeding amphibians can rapidly increase their numbers if the restoration is implemented at the landscape scale, taking into account the habitat requirements of target species and the ecological connectivity of populations. When the remnant populations are strong enough, translocation of individuals may not be necessary. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008     

High Prevalence of Batrachochytrium dendrobatidis in Wild Populations of Lowland Leopard Frogs Rana yavapaiensis in Arizona

Batrachochytrium dendrobatidis (Bd) is a fungus that can potentially lead to chytridiomycosis, an amphibian disease implicated in die-offs and population declines in many regions of the world. Winter field surveys in the last decade have documented die-offs in populations of the lowland leopard frog Rana yavapaiensis with chytridiomycosis. To test whether the fungus persists in host populations between episodes of observed host mortality, we quantified field-based Bd infection rates during nonwinter months. We used PCR to sample for the presence of Bd in live individuals from nine seemingly healthy populations of the lowland leopard frog as well as four of the American bullfrog R. catesbeiana (a putative vector for Bd) from Arizona. We found Bd in 10 of 13 sampled populations. The overall prevalence of Bd was 43% in lowland leopard frogs and 18% in American bullfrogs. Our results suggest that Bd is widespread in Arizona during nonwinter months and may become virulent only in winter in conjunction with other cofactors, or is now benign in these species. The absence of Bd from two populations associated with thermal springs (water >30°C), despite its presence in nearby ambient waters, suggests that these microhabitats represent refugia from Bd and chytridiomycosis.     

Fine structural distribution of the surface-connected canalicular system in frog thrombocytes

Summary The existence of the surface-connected canalicular system (SCCS) has been demonstrated in semithick sections of the frog thrombocytes by the use of a high voltage electron microscope. The SCCS of the thrombocytes in Rana catesbeiana and Rana nigromaculata consists of numerous canaliculi and vesicles with a diameter of 250 nm, which join with one another to make a complex network throughout the cytoplasm. Although the SCCS of Xenopus laevis fits well into the pattern described in Rana catesbeiana, the diameter of the canaliculi of the SCCS is about 500 nm. The results of this study suggest that the SCCS is a specific organelle of the thrombocyte system common to submammals and mammals.     

Water use and the thermoregulatory behaviour of kangaroos in arid regions: insights into the colonisation of arid rangelands in Australia by the Eastern Grey Kangaroo (Macropus giganteus)

The Eastern Grey Kangaroo (Macropus giganteus) occurs mostly in the wetter regions of eastern Australia. However, in the past 30–40 years it has moved into more arid regions (rainfall<250 mm), thus increasing its overlap zone with the xeric adapted Red Kangaroo (Macropus rufus). An increased access to water (supplied for domestic stock) may explain this range extension, but changes in the availability of preferred feed could also be involved. The water use, drinking patterns and thermoregulatory behaviour of these two species of kangaroo have been examined in a semi-free range study, during summer at an arid rangeland site. Foraging was largely nocturnal in both species and during the day they behaved to reduce heat loads. This was especially so for M. giganteus, which showed greater shade seeking. However, it still used more water (72±2.6 mL kg⁻¹ day⁻¹, mean ± SE) than M. rufus (56±7.6 mL kg⁻¹ day⁻¹) and drank twice as frequently. Although M. giganteus produced a less concentrated urine (1422±36 mosmol kg⁻¹) than M. rufus (1843±28 mosmol kg⁻¹), kidney physiology did not explain all of the differences in water metabolism between the species. Water from the feed and faecal water retention also appear to be involved. Broadly, a better access to reliable water and the utilisation of mesic microhabitats has enabled M. giganteus to make inroads into the changing rangelands of eastern Australia. However, changes in the vegetation, due to stock grazing, have also favoured M. giganteus, which is a grass eating specialist.     

Reproduction of plateau pika (<Emphasis Type="BoldItalic">Ochotona curzoniae</Emphasis>) on the Qinghai–Tibetan plateau

The reproduction of the plateau pika (Ochotona curzoniae) was investigated in Guoluo District at an elevation of 4,000 m on the Qinghai–Tibetan plateau, China, from April 2007 to August 2008. Reproduction was seasonal, and the breeding season lasted from April to late June/early July. Adults produced two litters in each year, and the mean litter size, estimated by counting the number of embryos in utero, was 3.3 ± 0.1 (n = 52) in 2007 and 3.2 ± 0.1 (n = 66) in 2008. The timing of reproduction showed high inter-annual variation; lower precipitation and the concomitant delay in spring vegetation phenology may have retarded the onset of the breeding season in 2007 compared with 2008. The most frequent litter sizes were 3 and 4, which together comprised 71.2% and 83.3% of litters in May and June of 2007 and 2008, respectively. Compared with previous studies, reproduction was highly variable between geographic areas. Pikas produced between one and five litters per year in different regions of the plateau over different breeding seasons. This geographic and inter-annual variation appeared to be associated with the duration of plant growth at each site, suggesting that plateau pikas adjust the length of their breeding season to match the period when sufficient energy is available to support the high energy demands of reproduction.     

Structure of vegetation patches in northwestern Patagonia, Argentina

Vegetation of arid and semiarid environments has in general a patchy distribution. Our objective was to (a) determine several qualitative and quantitative analytical characteristics of vegetation patches in an arid zone of Patagonia, Argentina, and (b) investigate relationships between them. Annual precipitation in this area was 200 mm during 1999–2005. Eight transects involving ten patches each were studied within a 15 × 15 km area. Mean (±1 SE) values (n = 80) in the vegetation patches were 315 ± 25 and 207 ± 16 cm for the greatest and lowest patch diameter, respectively; 23 ± 2 cm for mound height; 113 ± 12 cm for maximum vegetation height; and 170 ± 18 cm and 58 ± 2% for distance to the next vegetation patch and vegetation patch cover within a transect, respectively. Correlations between greatest and lowest diameters, mound height, maximum plant height and distance to the closest vegetation patch were all significant (P < 0.01; n = 80). In all vegetation patches, the greatest and lowest frequencies were found for the grass Stipa spp. (71.2%) and the shrub Grindelia chiloensis (Cornel.) Cabrera (12.5%). Stipa spp. and the shrub Atriplex lampa (Moq.) D. Dietr. showed the highest simultaneous frequency (50%). A reasonable association among species (>45%) was found for Stipa spp., Atriplex lampa and the shrubs Larrea divaricata Cav., Lycium chilense Miers ex Bertero and Junellia ligustrina (Lag.) Moldenke. Larrea divaricata and Atriplex lampa contributed more than 84% of the total patch standing crop (5,777 ± 435 g). Average patch size and specific diversity were 5.93 ± 0.33 m² and 1.31 ± 0.11, respectively. Aboveground standing crop of the two dominant shrubs decreased as plant species diversity increased (P < 0.05). Conservation of vegetation patches is crucial to prevent increased soil erosion and desertification in the study ecological system.     

Effects of the burrowing mayfly,Hexagenia, on nitrogen and sulfur fractions in lake sediment microcosms

Effects of the burrowing mayfly, Hexagenia, on nitrogen and sulfur fractions of sediment, and overlying water were determined. Laboratory microcosms were used to reproduce the benthic environment. The activities of Hexagenia increased sediment Eh (1.98 ± 0.486 (22) mV · day ⁻¹), and decreased pH in sediment (−0.007 ± 0.001 (22) day ⁻¹) and overlying water(-0.024 ± 0.004 (10) day⁻¹). In the control, Eh decreased and pH did not change. The presence of Hexagenia also markedly increased ammonia in sediment (5.46 ± 0.14 (22) ppm N · day⁻¹) and overlying water (0.792 ± 0.154 (10) ppm N · day⁻¹), while the control did not change. In addition, the sulfate fraction of sediment (0.177 ± 0.006 (17)% dry mass) and water (50.0 ± 4.9 (5) mg · I⁻¹) in microcosms with Hexagenia was greater than that of the control (0.151 ± 0.005 (16)% dry mass; 14.7 ± 1.71 (3) mg · 1⁻¹) at the termination of the experiment. Hexagenia may also stimulate the mineralization of carbon-bonded sulfur. The general role of Hexagenia in altering sediment chemistry is discussed.     

Factors affecting nesting success in the Great-crested Grebe Podiceps cristatus at Lake Tonga,north-east Algeria

The breeding ecology of the Great-crested Grebe Podiceps cristatus was investigated over four consecutive years (2009-2012) at Lake Tonga, north-east Algeria. In all four years, the egg-laying period was relatively short, spanning two months (end of March to end of May), and bimodal. Nests were mainly located in Phragmites australis, over water of substantial depth (178 ± 43?cm, N=209), far from the shore and in habitat with low vegetation cover (12.37 ± 7.67%, N=209). The overall clutch size was 3.73 ± 0.92 eggs (N=127) and it decreased marginally over time. The overall nesting success was 70.4% (N=209), with nest failure caused mainly by predation (65%) and flooding (23%). Breeding outcome was significantly and positively related to nest size, with bigger nests conferring better survival to eggs and young probably through affording better protection during spells of adverse weather. However, the benefits of bigger nests may be confounded by the age or intrinsic quality of birds. The location of nests in P. australis, rather than other vegetation types, increased nesting success marginally but significantly. Two cases of interspecific mixed clutches involving the Great-crested Grebe were recorded.