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SummaryAnimal mass mortality events (MMEs) will increase with weather and climate extremes. MMEs can add significant stress to ecosystems through extraordinary nutrient pulses or contribute to potential disease transmission risks. Given their efficient removal of carrion biomass from landscapes, we argue here for the potential of scavenger guilds to be a key nature-based solution to mitigating MME effects. However, we caution that scavenger guilds alone will not be a silver bullet. It is critical for further research to identify how the composition of scavenger guilds and the magnitude of MMEs will determine when scavengers will buffer the impacts of such events on ecosystems and when intervention might be required. Some MMEs are too large for scavengers to remove efficiently, and there is a risk of MMEs subsidizing pest species, altering nutrient cycling or leading to disease spread. Prioritizing native scavenger taxa in conservation management policies may help to boost ecosystem resilience through preserving their key ecological services. This should be part of a multi-pronged approach to MME mitigation that combines scavenger conservation with practices such as carcass dispersal or removal when exceeding a threshold quantity. Policymakers are urged to identify such thresholds and to recognize both the insects and the vertebrate scavengers that could act as allies for mitigating the emerging problem of climate-driven MMEs.

Australia’s 2019–20 mega-fires burnt 79% of the Greater Blue Mountains World Heritage Area, prompting an urgent need for rapid on-ground post-fire assessments of flora and fauna to aid in post-fire recovery. This project aimed to determine spatial patterns in populations and assemblages of vertebrates, vertebrate temporal activity, and the diet of the invasive Red Fox Vulpes vulpes, across burnt and unburnt sites. Using remote camera traps we surveyed 12 unburnt and 10 burnt sites approximately 12 months after the fires. We detected 41 species (11 mammals, 28 birds and 2 reptiles), with different species composition, but similar vertebrate species richness across both unburnt and burnt sites. The relative abundance of the Eastern Grey Kangaroo Macropus giganteus, Common Wombat Vombatus ursinus and Australian Magpie Gymnorhina tibicen was higher in burnt sites, while small mammals (< 500 g) had higher relative abundance at unburnt sites. There was no difference in the relative abundance of the Superb Lyrebird Menura novaehollandiae across burnt and unburnt sites, and although 11 species of bird were only detected at unburnt sites, the numbers were too low for reliable estimates of differences. Red Fox scat analysis (n=23) revealed that invertebrates and plant material were the dominant prey items in both burnt and unburnt sites, but medium-sized mammals increased in Red Fox diets in burnt sites, and reptiles were consumed disproportionately more by Red Foxes in burnt compared to unburnt sites. Although the short-term nature of this study and low scat sample size limited detailed insights, our rapid survey was an effective tool to gain preliminary data on species responses to the 2019–20 megafires in the Blue Mountains and contribute to a baseline for understanding species recovery.

We present an in-depth study of the late-time near-infrared plateau in Type Ia supernovae (SNe Ia), which occurs between 70-500 d. We double the existing sample of SNe Ia observed during the late-time near-infrared plateau with new observations taken with the Hubble Space Telescope, Gemini, New Technology Telescope, the 3.5m Calar Alto Telescope, and the Nordic Optical Telescope. Our sample consists of 24 nearby SNe Ia at redshift < 0.025. We are able to confirm that no plateau exists in the Ks band for most normal SNe Ia. SNe Ia with broader optical light curves at peak tend to have a higher average brightness on the plateau in J and H, most likely due to a shallower decline in the preceding 100 d. SNe Ia that are more luminous at peak also show a steeper decline during the plateau phase in H. We compare our data to state-of-the-art radiative transfer models of nebular SNe Ia in the near-infrared. We find good agreement with the sub-Mch model that has reduced non-thermal ionisation rates, but no physical justification for reducing these rates has yet been proposed. An analysis of the spectral evolution during the plateau demonstrates that the ratio of [Fe II] to [Fe III] contribution in a near-infrared filter determines the light curve evolution in said filter. We find that overluminous SNe decline slower during the plateau than expected from the trend seen for normal SNe Ia, 17 pages, 8 figures, Accepted for publication in MNRAS

Climate change impacts are accelerating and there is an urgent need to address this global issue. Tackling climate change in an effective and socially just manner needs to involve mitigation strategies that address the underlying causes of climate change, but also adaptation strategies that help us prepare for current and future impacts. Historically, mitigation and adaptation strategies have been treated separately, but there is now growing awareness of important synergies between them. We highlight these synergies across six key areas where humans need to make transformative changes in order to reduce the impacts of climate change, including energy, pollutants, nature, food, population and the economy. In doing so, we show the enormous potential for civil society, government, world leaders and the private sector to take advantage of the fact that mitigation strategies can also provide adaptation opportunities to lessen humanity’s suffering as we navigate the uncertainties of the climate crisis.

Context. Carrion is a high-energy and nutrient-rich resource that attracts a diverse group of vertebrate scavengers. However, despite the carrion pool being highly seasonal in its availability, there is little understanding of how scavengers utilise carcasses across all four seasons. Aim. To assess how season influences carcass-detection times by vertebrate scavengers and their rates of scavenging. Methods. We used remote cameras to monitor vertebrate scavenging at 15 eastern grey kangaroo (Macropus giganteus) carcasses in four consecutive seasons (summer, autumn, winter, and spring; total 58 carcasses) in the Australian Alps. Key results. In total, 745 599 remote-camera images were captured, within which 34 vertebrate species were identified, nine of which were recorded to actively scavenge. Time to first detection of carcasses by vertebrate scavengers was 5.3 and 9.6 times longer during summer (average 144 h) than during spring (average 34 h) and winter (average 24 h) respectively. Rates of vertebrate scavenging were highest in winter and spring, with brushtail possums (Trichosurus vulpecula) accounting for 78% of all scavenging events during winter, and ravens (Corvus spp.) accounting for 73% during spring. High rates of carcass use by these mesoscavengers may reflect a scarcity of other food sources, the demands of their breeding season, or a relative absence of scavenging by larger dominant species such as dingoes (Canis dingo) and wedge-tailed eagles (Aquila audax). Conclusions. These findings demonstrate the highly seasonal nature of vertebrate scavenging dynamics in an alpine ecosystem, and that mesoscavengers, not apex scavengers, can dominate the use of carcasses. Implications. Accounting for the effects of season is integral to understanding the way animals utilise carcasses in alpine and other strongly seasonal environments; and for developing further our knowledge of ecosystem processes linked to decomposition.

We present an analysis of the optical and UV properties of AT 2020wey, a faint and fast tidal disruption event (TDE) at 124.3 Mpc. The light curve of the object peaked at an absolute magnitude of $M_{g} = -17.45$ mag and a maximum bolometric luminosity of $L_{\rm peak}=(8.74\pm0.69)\times10^{42}$ erg s$^{-1}$, making it comparably faint with iPTF16fnl, the faintest TDE to date. The time from the last non-detection to the $g$-band peak is 22.94 $\pm$ 2.03 days and the rise is well described by $L\propto t^{1.8}$. The decline of the bolometric light curve is described by a sharp exponential decay steeper than the canonical $t^{-5/3}$ power law, making AT 2020wey the fastest declining TDE to date. Multi-wavelength fits to the light curve indicate a complete disruption of a star of $M_*=0.11M_{\odot}$ by a black hole of $M_{\rm BH}=10^{6.46}M_{\odot}$. Our spectroscopic dataset reveals broad ($\sim10^{4}$ km s$^{-1}$) Balmer and He II $\lambda$4686 lines, with H$\alpha$ reaching its peak with a lag of $\sim8.2$ days compared to the continuum. In contrast to previous faint and fast TDEs, there are no obvious Bowen fluorescence lines in the spectra of AT 2020wey. There is a strong correlation between the MOSFIT-derived black hole masses of TDEs and their decline rate. However, AT 2020wey is an outlier in this correlation, which could indicate that its fast early decline may be dictated by a different physical mechanism than fallback. After performing a volumetric correction to a sample of 30 TDEs observed between 2018 and 2020, we conclude that faint TDEs are not rare by nature and that they should constitute up to $\sim$ 50 - 60 % of the entire population and their numbers could alleviate some of the tension between the observed and theoretical TDE rate estimates. We calculate the optical TDE luminosity function and we find a steep power-law relation $dN/dL_{g} \propto {L_{g}}^{-2.36}$., Comment: Accepted for publication to A&A (21/02/2023)

Two introduced carnivores, the European red fox Vulpes vulpes and domestic cat Felis catus, have had extensive impacts on Australian biodiversity. In this study, we collate information on consumption of Australian birds by the fox, paralleling a recent study reporting on birds consumed by cats. We found records of consumption by foxes on 128 native bird species (18% of the non-vagrant bird fauna and 25% of those species within the fox’s range), a smaller tally than for cats (343 species, including 297 within the fox’s Australian range, a subset of that of the cat). Most (81%) bird species eaten by foxes are also eaten by cats, suggesting that predation impacts are compounded. As with consumption by cats, birds that nest or forage on the ground are most likely to be consumed by foxes. However, there is also some partitioning, with records of consumption by foxes but not cats for 25 bird species, indicating that impacts of the two predators may also be complementary. Bird species ≥3.4 kg were more likely to be eaten by foxes, and those

Few animals in Australia evoke as much controversy as the dingo. There are debates about its cultural significance, what to call it, and its ecological and economic impacts. Resolving these debates requires consensus and agreement among researchers, land managers and other stakeholders. To aid this, I briefly summarise how far we have come in terms of increasing our knowledge of the ecology and behaviour of dingoes since the Royal Zoological Society of New South Wales held its first symposium on the dingo in 1999. I summarise the key debates that have arisen during this period, and then summarise some of the key recommendations made in papers that were written following the 2019 symposium. I finish with some suggestions for future dingo research, focusing on (1) how we can better understand and appropriately acknowledge the cultural significance of the dingo through research, broader consultations and appropriate representations on national, state and local pest planning committees, (2) produce taxonomic consensus through the appointment of an independent panel and future research using genome-wide DNA technology, and (3) resolving ecological and economic debates via reintroduction experiments in both conservation and managed agricultural landscapes. Without such efforts, I see a future for the dingo that continues to be steeped in controversy and debate.

We propose a relational graph to incorporate clinical similarity between patients while building personalized clinical event predictors with a focus on hospitalized COVID-19 patients. Our graph formation process fuses heterogeneous data, i.e., chest X-rays as node features and non-imaging EHR for edge formation. While node represents a snap-shot in time for a single patient, weighted edge structure encodes complex clinical patterns among patients. While age and gender have been used in the past for patient graph formation, our method incorporates complex clinical history while avoiding manual feature selection. The model learns from the patient’s own data as well as patterns among clinically-similar patients. Our visualization study investigates the effects of ‘neighborhood’ of a node on its predictiveness and showcases the model’s tendency to focus on edge-connected patients with highly suggestive clinical features common with the node. The proposed model generalizes well by allowing edge formation process to adapt to an external cohort.

Context Invasive species are a major cause of biodiversity loss across much of the world, and a key threat to Australia’s diverse reptile fauna. There has been no previous comprehensive analysis of the potential impact of the introduced European red fox, Vulpes vulpes, on Australian reptiles. Aims We seek to provide an inventory of all Australian reptile species known to be consumed by the fox, and identify characteristics of squamate species associated with such predation. We also compare these tallies and characteristics with reptile species known to be consumed by the domestic cat, Felis catus, to examine whether predation by these two introduced species is compounded (i.e. affecting much the same set of species) or complementary (affecting different groups of species). Methods We collated records of Australian reptiles consumed by foxes in Australia, with most records deriving from fox dietary studies (tallying >35 000 samples). We modelled presence or absence of fox predation records against a set of biological and other traits, and population trends, for squamate species. Key results In total, 108 reptile species (~11% of Australia’s terrestrial reptile fauna) have been recorded as consumed by foxes, fewer than that reported for cats (263 species). Eighty-six species have been reported to be eaten by both predators. More Australian turtle species have been reported as consumed by foxes than by cats, including many that suffer high levels of predation on egg clutches. Twenty threatened reptile species have been reported as consumed by foxes, and 15 by cats. Squamate species consumed by foxes are more likely to be undergoing population decline than those not known to be consumed by foxes. The likelihood of predation by foxes increased with squamate species’ adult body mass, in contrast to the relationship for predation by cats, which peaked at ~217 g. Foxes, but not cats, were also less likely to consume venomous snakes. Conclusions The two introduced, and now widespread, predators have both compounding and complementary impacts on the Australian reptile fauna. Implications Enhanced and integrated management of the two introduced predators is likely to provide substantial conservation benefits to much of the Australian reptile fauna.

Species traits have much to offer conservation science. However, the selection and application of trait data in conservation requires rigor to avoid perverse or unexpected outcomes. To guide trait use, we review how traits are applied along the conservation continuum: the progression of conservation actions from assessing risk, to designing and prioritizing actions, to implementation and evaluation. We then provide a framework for their use as proxies for more nuanced empirical data on species and ecosystems. Framework steps include (1) identifying information needs relative to conservation goals, (2) choosing relevant traits using theory and expanding via expert elicitation, and (3) defining and addressing the limits of trait information. Worked examples for contemporary plant and amphibian conservation show how traits should be selected and applied based on theory and/or evidence (rather than data availability or untested assumptions). Finally, we forecast the use of trait data in several conservation applications globally.

Dead animal biomass (carrion) is present in all terrestrial ecosystems, and its consumption, decomposition, and dispersal can have measurable effects on vertebrates, invertebrates, microbes, parasites, plants, and soil. But despite the number of studies examining the influence of carrion on food webs, there has been no attempt to identify how general ecological processes around carrion might be used as an ecosystem indicator. We suggest that knowledge of scavenging and decomposition rates, scavenger diversity, abundance, and behavior around carrion, along with assessments of vegetation, soil, microbe, and parasite presence, can be used individually or in combination to understand food web dynamics. Monitoring carrion could also assist comparisons of ecosystem processes among terrestrial landscapes and biomes. Although there is outstanding research needed to fully integrate carrion ecology and monitoring into ecosystem management, we see great potential in using carrion as an ecosystem indicator of an intact and functional food web., We argue that information about the processes and organisms involved with the consumption and decomposition of dead animal matter (carrion) can provide insights into the broader health and integrity of ecosystems.

Introduction of the domestic cat and red fox has devastated Australian native fauna. We synthesized Australian diet analyses to identify traits of prey species in cat, fox and dingo diets, which prey were more frequent or distinctive to the diet of each predator, and quantified dietary overlap. Nearly half (45%) of all Australian terrestrial mammal, bird and reptile species occurred in the diets of one or more predators. Cat and dingo diets overlapped least (0.64 ± 0.27, n = 24 location/time points) and cat diet changed little over 55 years of study. Cats were more likely to have eaten birds, reptiles and small mammals than foxes or dingoes. Dingo diet remained constant over 53 years and constituted the largest mammal, bird and reptile prey species, including more macropods/potoroids, wombats, monotremes and bandicoots/bilbies than cats or foxes. Fox diet had greater overlap with both cats (0.79 ± 0.20, n = 37) and dingoes (0.73 ± 0.21, n = 42), fewer distinctive items (plant material, possums/gliders) and significant spatial and temporal heterogeneity over 69 years, suggesting the opportunity for prey switching (especially of mammal prey) to mitigate competition. Our study reinforced concerns about mesopredator impacts upon scarce/threatened species and the need to control foxes and cats for fauna conservation. However, extensive dietary overlap and opportunism, as well as low incidence of mesopredators in dingo diets, precluded resolution of the debate about possible dingo suppression of foxes and cats.

The response of beta cells to inflammatory cytokines contributes to type 1 diabetes (T1D) risk, but the specific genes that underlie this response and mediate beta cell survival remain largely unknown. In this study we used a suite of functional genomics assays combined with human genetics, to map cis-regulatory programs in beta cells and to identify T1D genes that affect beta cell survival upon exposure to the pro-inflammatory cytokines IL1β, IFNγ and TNFα. We mapped 38,931 cytokine-responsive candidate cis­­ -regulatory elements (cCREs) active in beta cells using ATAC-seq and single nuclear ATAC-seq (snATAC-seq) , and linked cytokine-responsive beta cell cCREs to putative target genes using single cell co-accessibility and HiChIP. We performed a genome-wide pooled CRISPR loss-of-function screen in EndoC-βH1 cells, which identified 867 genes affecting cytokine-induced beta cell loss. Genes that promoted beta cell survival and had up-regulated expression in cytokine exposure were specifically enriched at T1D loci, and these genes were preferentially involved in inhibiting inflammatory response, ubiquitin-mediated proteolysis, mitophagy and autophagy. We identified 2,229 variants in cytokine-responsive beta cell cCREs altering transcription factor (TF) binding using high-throughput SNP-SELEX, and variants altering binding of TF families regulating stress, inflammation and apoptosis were broadly enriched for T1D association. Finally, through integration with genetic fine mapping, we identified T1D risk variants regulating beta cell survival in cytokine exposure. At the 16p13 locus, a T1D variant affected TF binding in a cytokine-induced beta cell cCRE that physically interacted with the SOCS1 promoter, and increased SOCS1 activity promoted beta cell survival in cytokine exposure. Together our findings reveal processes and genes acting in beta cells during cytokine exposure that intrinsically modulate risk of T1D. Disclosure P.Benaglio: None. M.Donovan: None. J.Chiou: Employee; Pfizer Inc. J.M.Newsome ashmus: None. J.Kaur: None. S.Corban: None. B.Ren: Stock/Shareholder; Arima Genomics, Epigenome Technologies. K.Frazer: n/a. M.Sander: None. K.J.Gaulton: Consultant; Genentech, Inc., Stock/Shareholder; Neurocrine Biosciences, Inc., Vertex Pharmaceuticals Incorporated. H.Zhu: None. M.Okino: None. J.Yan: None. R.Elgamal: None. N.Nariai: None. E.Beebe: None. K.Korgaonkar: None. Y.Qiu: None. Funding NIH DK122607

The red fox Vulpes vulpes is one of the world’s most widespread carnivores. A key to its success has been its broad, opportunistic diet. The fox was introduced to Australia about 150 years ago, and within 30 years of its introduction was already recognised as a threat to livestock and native wildlife. We reviewed 85 fox diet studies (totalling 31693 samples) from throughout the species’ geographic range within Australia. Mammals were a major component of fox diet, being present in 70 ± 19% of samples across n = 160 locations. Invertebrates (38 ± 26% n = 130) and plant material (26 ± 25% n = 123) were also both staple foods and often the dominant food category recorded. Birds (13 ± 11% n = 137) and reptiles (10 ± 15% n = 132) were also commonly reported, while frogs were scarcely represented (1.6 ± 3.6% n = 111) in fox diet studies. Biogeographical differences reveal factors that likely determine prey availability. Diet composition varied with ecosystem, level of vegetation clearing and condition, and climate zone. Sample type (i.e. stomach versus scat samples) also significantly influenced reporting of diet composition. Livestock and frogs were underrepresented in records based on analysis of scats, whereas small mammals (native rodents, dasyurid marsupials, and bats) were more likely to be recorded in studies of scats than in studies of stomach contents. Diet varied seasonally, reflecting activity patterns of prey species and food availability. This synthesis also captures temporal shifts in fox diet over 70 years (1951–2020), as foxes have switched to consuming more native species in the wake of successful broadscale biological control of the invasive European rabbit Oryctolagus cuniculus. Diet analyses, such as those summarised in this review, capture the evidence required to motivate for greater control of foxes in Australia. This synthesis also highlights the importance of integrated pest species management to meet biodiversity conservation outcomes.

Dingoes (Canis dingo) are known for hunting and killing animals to meet their energetic requirements, but like almost all predators they also scavenge animal remains. To improve our understanding of dingo scavenging ecology, we investigated the role of abiotic and biotic factors in shaping carcass utilisation by dingoes and further determined whether dingo scavenging influenced carcass persistence in the landscape. To do so, we monitored visitation and scavenging by dingoes using remote cameras positioned on 119 kangaroo carcasses in open and closed canopy habitats and in warm and cool seasons. The carcasses were monitored across multiple study sites, which incorporated forest, alpine and desert ecoregions in Australia. We found that season played an important role in shaping carcass utilisation by dingoes, as well as carcass persistence. Warmer seasons increased the rate of carcass discovery 6.3-fold in the Forest study site and 4.8-fold in the Alpine study site, and also increased the time dingoes spent feeding on carcasses in the Alpine study site. Further, across all study sites, carcasses persisted at least 4.7 times longer in cool compared with warm seasons. On the other hand, carcass utilisation by dingoes was not influenced by habitat, although carcasses were more likely to persist in open compared with closed canopy habitats in the Alpine study site. Finally, our study showed that dingo scavenging may contribute to substantial carcass removal in certain contexts. Indeed, decreased carcass persistence in the Forest study site was evident in the cool season, when dingo scavenging occurred during the first two weeks of monitoring. The variability in results highlights the complexity of patterns in dingo scavenging and, more broadly, of vertebrate scavenging. It emphasises the need to consider multiple abiotic and biotic factors to properly understand the functional roles of different scavenger species. Longer-term studies with additional seasonal replicates may also yield a more detailed picture of the role of dingoes as apex scavengers.

Context It is widely recognised that red foxes (Vulpes vulpes) are abundant within urban areas; however, it is difficult to apply lethal control measures using poison baits in cities because of concerns about the safety of domestic pets, particularly dogs (Canis familiaris). Aims We tested canid pest ejectors (CPEs) as a potential method of fox control by measuring visitation and activation behaviour of foxes and other wildlife while assessing non-target risk to domestic dogs. Methods We compared eight urban and eight peri-urban sites in Sydney, with half of the sites having restricted access for domestic dogs. We allocated five camera traps and ejectors per site. Through generalised linear mixed models, we compared the probability of ejector activation between foxes and dogs. We also assessed the relationship between dog visitation and distance to habitation and dog restrictions as measures of dog safety. Key results Both species of canids were equally likely to pull the ejector (P = 0.26). As expected, dog visitation was significantly lower in sites with dog restrictions (P

Synopsis Many large predators are also facultative scavengers that may compete with and depredate other species at carcasses. Yet, the ecological impacts of facultative scavenging by large predators, or their “scavenging effects,” still receive relatively little attention in comparison to their predation effects. To address this knowledge gap, we comprehensively examine the roles played by, and impacts of, facultative scavengers, with a focus on large canids: the African wild dog (Lycaon pictus), dhole (Cuon alpinus), dingo (Canis dingo), Ethiopian wolf (Canis simensis), gray wolf (Canis lupus), maned wolf (Chrysocyon brachyurus), and red wolf (Canis rufus). Specifically, after defining facultative scavenging as use or usurpation of a carcass that a consumer has not killed, we (1) provide a conceptual overview of the community interactions around carcasses that can be initiated by facultative scavengers, (2) review the extent of scavenging by and the evidence for scavenging effects of large canids, (3) discuss external factors that may diminish or enhance the effects of large canids as scavengers, and (4) identify aspects of this phenomenon that require additional research attention as a guide for future work.

We present photometric and spectroscopic data on three extragalactic luminous red novae (LRNe): AT 2018bwo, AT 2021afy, and AT 2021blu. AT 2018bwo was discovered in NGC 45 (at about 6.8 Mpc) a few weeks after the outburst onset. During the monitoring period, the transient reached a peak luminosity of 1040 erg s−1. AT 2021afy, hosted by UGC 10043 (∼49.2 Mpc), showed a double-peaked light curve, with the two peaks reaching a similar luminosity of 2.1(±0.6)×1041 erg s−1. Finally, for AT 2021blu in UGC 5829 (∼8.6 Mpc), the pre-outburst phase was well-monitored by several photometric surveys, and the object showed a slow luminosity rise before the outburst. The light curve of AT 2021blu was sampled with an unprecedented cadence until the object disappeared behind the Sun, and it was then recovered at late phases. The light curve of LRN AT 2021blu shows a double peak, with a prominent early maximum reaching a luminosity of 6.5 × 1040 erg s−1, which is half of that of AT 2021afy. The spectra of AT 2021afy and AT 2021blu display the expected evolution for LRNe: a blue continuum dominated by prominent Balmer lines in emission during the first peak, and a redder continuum consistent with that of a K-type star with narrow absorption metal lines during the second, broad maximum. The spectra of AT 2018bwo are markedly different, with a very red continuum dominated by broad molecular features in absorption. As these spectra closely resemble those of LRNe after the second peak, AT 2018bwo was probably discovered at the very late evolutionary stages. This would explain its fast evolution and the spectral properties compatible with that of an M-type star. From the analysis of deep frames of the LRN sites years before the outburst, and considerations of the light curves, the quiescent progenitor systems of the three LRNe were likely massive, with primaries ranging from about 13 M⊙ for AT 2018bwo, to 14−1+4 M⊙ for AT 2021blu, and over 40 M⊙ for AT 2021afy.

We present a sample of Type Icn supernovae (SNe Icn), a newly-discovered class of transients characterized by their interaction with H- and He-poor circumstellar material (CSM). This sample is the largest collection of SNe Icn to date and includes observations of two published objects (SN 2019hgp and SN 2021csp) as well as two objects (SN 2019jc and SN 2021ckj) not yet published in the literature. The SNe Icn display a range of peak luminosities, rise times, and decline rates, as well as diverse late-time spectral features. To investigate their explosion and progenitor properties we fit their bolometric light curves to a semi-analytical model consisting of luminosity inputs from circumstellar interaction and radioactive decay of $^{56}$Ni. We infer low ejecta masses ($\lesssim$ 2 M$_\odot$) and $^{56}$Ni masses ($\lesssim$ 0.04 M$_\odot$) from the light curves, suggesting that normal stripped-envelope supernova (SESN) explosions within a dense CSM cannot be the underlying mechanism powering SNe Icn. Additionally, we find that an upper limit on the star formation rate density at the location of SN 2019jc lies at the lower end of a distribution of SESNe, in conflict with a massive star progenitor of this object. Based on the estimated ejecta masses, $^{56}$Ni masses, and explosion site properties, we favor a low-mass, ultra-stripped star as the progenitor of some SNe Icn. For others, we suggest that a Wolf-Rayet star progenitor may better explain their observed properties. This study demonstrates that multiple progenitor channels may produce SNe Icn and other interaction-powered transients., 25 pages, 11 figures, published in ApJ