Dai K.J. Morgan

Comparing plasma and faecal measures of steroid hormones in Adelie penguins Pygoscelis adeliae

Physiological measurements of both stress and sex hormones are often used to estimate the consequences of natural or human-induced change in ecological studies of various animals. Different methods of hormone measurement exist, potentially explaining variation in results across studies; methods should be cross-validated to ensure that they correlate. We directly compared faecal and plasma hormone measurements for the first time in a wild free-living species, the Adelie penguin (Pygoscelis adeliae). Blood and faecal samples were simultaneously collected from individual penguins for comparison and assayed for testosterone and corticosterone (or their metabolites). Sex differences and variability within each measure, and correlation of values across measures were compared. For both hormones, plasma samples showed greater variation than faecal samples. Males had higher mean corticosterone concentrations than females, but the difference was only statistically significant in faecal samples. Plasma testosterone, but not faecal testosterone, was significantly higher in males than females. Correlation between sample types was poor overall, and weaker in females than in males, perhaps because measures from plasma represent hormones that are both free and bound to globulins, whereas measures from faeces represent only the free portion. Faecal samples also represent a cumulative measure of hormones over time, as opposed to a plasma ‘snapshot’ concentration. Our data indicate that faecal sampling appears more suitable for assessing baseline hormone concentrations, whilst plasma sampling may best define immediate responses to environmental events. Consequently, future studies should ensure that they select the most appropriate matrix and method of hormone measurement to answer their research questions.

The relative importance of Australian magpies (Gymnorhina tibicen) as nest predators of rural birds in New Zealand

Abstract Australian magpies (Gymnorhina tibicen) have been recorded as predators at nests of other birds in New Zealand but their importance as a predator in rural areas, where they are most common, has not been previously quantified. We continuously monitored 38 nests of seven species in rural areas over two successive breeding seasons using time‐lapse video recording to determine the proportion that were preyed on by magpies compared to other animals in this ecosystem. Twenty‐two lethal events were recorded over the two breeding seasons; magpies were responsible for only one of these. A further eight scavenging events were also recorded; magpies were not responsible for any of these. Harriers (Circus approximans), ship rats (Rattus rattus), and cats (Felis catus) were the main predators and were responsible for 36, 32, and 23% of lethal events respectively. A pukeko (Porphyrio porphyrio) was also recorded preying on nest contents on one occasion. Other known nest predators such as Norway rats (Rattus norvegicus), possums (Trichosurus vulpecula), hedgehogs (Erinaceus eu‐ropaeus) and ruru (Ninox novaeseelandiae) did not appear in any recorded frame although present in the study areas. Our results suggest that magpies are not serious nest predators in rural areas in comparison to ship rats, cats, and harriers, and that controlling magpies in rural areas will not significantly improve the nesting success of other birds.

An inventory of mammalian pests in a New Zealand city

Abstract Urban ecosystems include many habitat types supporting native flora and fauna. These habitats may also sustain populations of introduced mammalian pests, although relatively little is known about the composition or distributions of these species in urban environments. We made a preliminary survey of the distribution and relative abundance of pest mammals across three urban habitat types (gully, amenity park, residential) in Hamilton, New Zealand. Tracking tunnel and WaxTag® surveys showed that: (1) rats (Rattus rattus or R. norvegicus), mice (Mus musculus) and brushtail possums (Tricho‐surus vulpecula) were detected most often and in highest abundances in gullies, were relatively rare in amenity parks, and were not detected in residential areas; (2) hedgehogs (Erinaceus europaeus) were regularly detected in all habitats; and (3) mustelids were not detected in any habitat. Live trapping in areas where rats were detected captured 21 rats, of which 19 were R. rattus. Scat and animal sign surveys found evidence of lagomorphs in amenity parks and gullies but not in residential areas. Cats (Felis catus) were detected in all habitats. These data suggest that important mammalian pests other than cats are either absent (mustelids) or comparatively rare (rats) in urban Hamilton and largely confined to gully habitats. Further research is needed to determine whether detection probabilities of target species vary significantly between the species and habitats we sampled, and to quantify the impact that mammalian pests might have in limiting populations of other animals, especially avifauna.

Do heterospecific size and demeanour influence visitation behaviour of birds at urban foraging patches

We compared the feeding behaviour of garden birds in the presence of four heterospecific decoy species at suburban feeding stations to assess the relative importance of body size (large vs. small) and demeanour (high vs. low potential for inter-specific aggression) as cues for threat recognition. We conducted separate trials with live, caged Australian magpie, Cracticus tibicen, and common myna, Acridotheres tristis, large and small species known to chase and harass heterospecifics, and comparably sized species not known for inter-species aggression (i.e. rock dove, Columba livia, and ringneck dove, Streptopelia risoria). Birds of all species arrived at feeding stations sooner and displayed higher-risk activities in the presence of small decoys. The two most common species that visited the feeding stations, silvereye, Zosterops lateralis, and house sparrow, Passer domesticus, were most likely to perform high-risk behaviours (i.e. landing on the stimulus cage and feeding from the station) in the presence of common mynas. The activities were performed least frequently in the presence of Australian magpies. As garden birds likely had the most experience interacting with common mynas, the results suggest that a two-step decision rule, with size and familiarity as important cues, may be used to recognize potential threats.

Environmental influences on Adelie penguin breeding schedules, endocrinology, and chick survival

To understand how the social and physical environment influences behaviour, reproduction and survival, studies of underlying hormonal processes are crucial; in particular, interactions between stress and reproductive responses may have critical influences on breeding schedules. Several authors have examined the timing of breeding in relation to environmental stimuli, while others have independently described endocrine profiles. However, few studies have simultaneously measured endocrine profiles, breeding behaviour, and offspring survival across seasons. We measured sex and stress hormone concentrations (oestrogens, testosterone, and corticosterone), timing of breeding, and chick survival, in Adelie penguins (Pygoscelis adeliae) at two colonies in two different years. Clutch initiation at Cape Bird South (CBS; year 1, ~14,000 pairs) occurred later than at Cape Crozier East (CCE; year 2, ~ 25,000 pairs); however, breeding was more synchronous at CBS. This pattern was probably generated by the persistence of extensive sea ice at CBS (year 1). Higher corticosterone metabolite and lower sex hormone concentrations at CBS correlated with later breeding and lower chick survival compared to at CCE - again, a likely consequence of sea ice conditions. Within colonies, sub-colony size (S, 50-100; M, 200-300; L, 500-600; XL, >1000 pairs) did not influence the onset or synchrony of breeding, chick survival, or hormone concentrations. We showed that the endocrine profiles of breeding Adelie penguins can differ markedly between years and/or colonies, and that combining measures of endocrinology, behaviour, and offspring survival can reveal the mechanisms and consequences that different environmental conditions can have on breeding ecology.

Can redirected aggression explain interspecific attacks by Australian magpies on other birds

Attacks by participants of conflicts against a third party are referred to as redirected aggression. Usually the third party is a conspecific — few documented cases of redirected aggression against other species exist. The Australian magpie (Gymnorhina tibicen), however, often attacks other species; the reasons for attacks are largely unknown. Some attacks occur after territorial disputes with conspecifics, suggesting that attacks are the result of redirected aggression. We subjected eight Australian magpie groups to simulated territorial intrusions. In one treatment an Australian magpie and rock dove (Columba livia) were presented in cages next to one another (5 m apart) on the territory for 30 min; the Australian magpie decoy was then covered and aggressive responses toward the rock dove by residents were recorded for a further 30 min (Treatment 1). Two additional treatments were presented in an identical manner on each territory where both decoys were either Australian magpies (Treatment 2) or rock doves (Treatment 3). We predicted that if Australian magpies regularly redirect aggression onto benign species after conspecific territorial intrusions, attack rates on the rock dove decoy in Treatment 1 would be higher than attack rates on the rock dove decoy in Treatment 3. Residents were seldom recorded close (<1 m) and not seen attacking rock dove decoys during tests. In contrast, Australian magpie decoys were often approached and attacked by residents. After a decoy was covered (following the first 30 min phase), residents spent little time in close proximity (on cage, <0.3 m, or 0.3-1 m) to the rock dove decoy in either Treatment 1 or Treatment 3; in contrast, residents were often recorded close to the Australian magpie decoy in Treatment 2. We found no evidence that Australian magpies redirect aggression onto other birds after territorial intrusions. The true proportion of territorial disputes leading to redirected attacks may be small, or only occur under highly specific contexts.

The palatability of flavoured novel floating pellets made with brewer's spent grain to captive carp

Abstract The palatability to common carp, Cyprinus carpio L. of three newly developed differently flavoured floating pellets made from a high proportion (40%) of brewers spent grain (BSG) was tested using a multiple-offer feeding experiment. The addition of ‘bold’ flavours, such as vanilla or strawberry essence, may help mask the unpleasant taste of some piscicides; however, their inclusion must not compromise uptake by carp. There were no significant differences between the consumption rates of the three varieties, and all flavours were readily consumed. Therefore, it is suggested that highly flavoured pellets made with BSG have a strong potential to mask the flavour of an unpalatable toxin, and further research is now needed to test this hypothesis.

Toxicity effects of oral gavage of aqueous solutions of cube-root powder and sodium nitrite in common carp.

Abstract Context. Common carp (Cyprinus carpio) is a highly invasive freshwater pest fish that has been linked to waterway degradation when it has been introduced and exists at high densities. The deployment of a toxic bait may be a logistically simple tool that wildlife managers could use to reduce carp populations. Rotenone, the piscicide most commonly used in previous attempts to produce a carp bait is very expensive, albeit highly toxic to carp. We investigated the toxicity of two potential alternative piscicides to carp. Aim. To determine the oral toxicity of two alternative cheaper toxins to carp, cube-root powder (CRP) and sodium nitrite (nitrite). Methods. CRP or nitrite was administered in an aqueous solution by gavage to lightly sedated captive carp. The aqueous solution consisted of a 30 : 70 mixture (w/w) of the surfactant, Polysorbate 80, to increase the absorption of toxins through the intestine, and water. Key results. The LD50 of CRP and nitrite in carp was 135.7 mg kg–1 and 122.0 mg kg–1, respectively. Conclusions. Both CRP and nitrite are toxic to carp at dose rates low enough to be incorporated into a piscicide bait for this species. Implications. Both CRP and nitrite appear to be viable alternative oral piscicides to rotenone for carp and warrant further investigation of delivery in bait.