Relationship between exploratory activity and adrenocortical activity in the black rat (Rattus rattus)

The relationship between physiological and behavioral stress markers is documented in several rodent species. However, there is no information regarding the role of adrenocortical activity in behavior of the black rat (Rattus rattus). Therefore, we hypothesize that the adrenocortical activity of black rats varies between individuals and is related to some of the behaviors in a novel environment. To test this hypothesis, we (i) validated a method for quantifying glucocorticoid metabolites from feces (fGCMs) with an enzyme immunoassay (EIA); (ii) examined variation and diurnal rhythms of feces and GCM production; and (iii) examined the relationship between GCM levels and exploratory behavioral traits. We fulfilled the first aim (i) by successfully performing an ACTH challenge test to validate the use of a 5α-pregnane-3β,11β,21-triol-20-one EIA for measuring fGCMs. Second (ii) we detected considerable consistent interindividual variability in production of both feces and glucocorticoids. The peak production of feces occurred in the first hour of the dark cycle, the peak of fGCMs occurred approximately 3 h later. Lastly, (iii) there was no clear relationship between behavior in the hole board test and GCMs. Grooming, a typical behavioral stress marker, was negatively associated with stress reactivity, while head-dipping in the hole-board test (traditionally considered an exploratory behavior independent of stress) was not correlated with the GCMs. This study offers a first look at GCMs in the black rat, successfully validates a method for their measurement and opens possibilities for future research of the relationship between glucocorticoids and exploratory behavior in this species.

Climate oscillation and the invasion of alien species influence the oceanic distribution of seabirds

Spatial and temporal distribution of seabird transiting and foraging at sea is an important consideration for marine conservation planning. Using at-sea observations of seabirds (n = 317), collected during the breeding season from 2012 to 2016, we built boosted regression tree (BRT) models to identify relationships between numerically dominant seabird species (red-footed booby, brown noddy, white tern, and wedge-tailed shearwater), geomorphology, oceanographic variability, and climate oscillation in the Chagos Archipelago. We documented positive relationships between red-footed booby and wedge-tailed shearwater abundance with the strength in the Indian Ocean Dipole, as represented by the Dipole Mode Index (6.7% and 23.7% contribution, respectively). The abundance of red-footed boobies, brown noddies, and white terns declined abruptly with greater distance to island (17.6%, 34.1%, and 41.1% contribution, respectively). We further quantified the effects of proximity to rat-free and rat-invaded islands on seabird distribution at sea and identified breaking point distribution thresholds. We detected areas of increased abundance at sea and habitat use-age under a scenario where rats are eradicated from invaded nearby islands and recolonized by seabirds. Following rat eradication, abundance at sea of red-footed booby, brown noddy, and white terns increased by 14%, 17%, and 3%, respectively, with no important increase detected for shearwaters. Our results have implication for seabird conservation and island restoration. Climate oscillations may cause shifts in seabird distribution, possibly through changes in regional productivity and prey distribution. Invasive species eradications and subsequent island recolonization can lead to greater access for seabirds to areas at sea, due to increased foraging or transiting through, potentially leading to distribution gains and increased competition. Our approach predicting distribution after successful eradications enables anticipatory threat mitigation in these areas, minimizing competition between colonies and thereby maximizing the risk of success and the conservation impact of eradication programs.

Bird-repellent effects on bait efficacy for control of invasive mammal pests

BACKGROUND

Repellents to reduce crop damage from birds and mammals have been investigated extensively, but their efficacy in reducing risk to non-target birds in aerial poisoning operations for control of mammal pests is less known. We assessed the impact on bait acceptability, palatability and kill efficacy for captive wild rats (Rattus rattus L.) and possums (Trichosurus vulpecula Kerr) of adding bird repellents (anthraquinone and d-pulegone) to baits used for their control in food choice trials.

RESULTS

For possums, anthraquinone at 0.25% reduced acceptability and palatability but not the efficacy of poison baits, whereas d-pulegone at 0.17% had no significant effects. Rats showed little response to d-pulegone, but developed a marked aversion to prefeed baits containing anthraquinone at both 0.1 and 0.25%, such that almost no exposed rats ate poison baits and mortality was reduced significantly. The aversion induced by anthraquinone was generalised to the bait, as anthraquinone-exposed rats did not eat bait with only d-pulegone.

CONCLUSION

Anthraquinone is not suitable for inclusion in bait for rat control at the concentrations tested, and also presents some risk to efficacy for possum control. D-pulegone would be suitable for inclusion in bait for possums and rats, but problems related to its volatility in bait manufacture and storage would need to be overcome. Further studies should focus on an alternative secondary repellent, or on establishing the maximum anthraquinone concentration that does not reduce efficacy for rats and testing whether or not that concentration is sufficient to repel native birds from baits reliably.