Cryptolestes dissimulatus

Social power among animal species has usually been characterized as being either male or female dominated. However, a new study published in the journal <a href="http://dx.doi.org/10.1016/j.tree.2022.04.004">Trends in Ecology &amp; Evolution</a> argues that such a binary understanding of <a href="https://www.earth.com/news/inequality-among-animals-can-shed-light-on-social-evolution/">inequality</a> in the degree of control or power that members of one sex exert over members of the other sex is too simplistic, failing to properly characterize the complex distribution of power between sexes.&nbsp;



The experts propose a new framework for assessing dominance, which places each species on a continuum, ranging from strict male to strict female dominance.&nbsp;



“Progress in this area has long been hampered by a binary vision of power asymmetries between the sexes, where most species were dominated by males and female dominance was anecdotal. This simplistic view has been reinforced by stereotypes that researchers carry because of the society in which they live and then unconsciously project onto the animals they're studying," explained study senior author Elise Huchard, a behavioral ecologist at the <a href="https://isem-evolution.fr/en/">Institute of Evolutionary Science of Montpellier</a> (ISEM).



According to Dr. Huchard, the distribution of power between the sexes has not been properly quantified in previous studies. By providing a comprehensive definition of intersexual power, together with a framework to measure it across various animal species, the researchers argued that each species could be placed on a continuum from strict male dominance to strict female dominance, so that hypotheses regarding how females or males can empower themselves can be better assessed.



While for males, the path to power seems rather simple and straightforward, involving physical dominance and coercion, for females the methods of establishing social power are more diverse, involving physiological, morphological, behavioral, and socio-ecological routes.&nbsp;



In the case of species where females are dominant, such as bonobos, hyenas, or lemurs, reproductive control (control over when and with which partners to mate) appears to be the main strategy for securing power. This comes in the form of resistance to mating, promiscuity, or even, in the case of hyenas, the evolution of genitals designed specifically for females to control fertilization.



“We hope that this framework will be used to quantify intersexual power in reproductive and social contexts and to facilitate the study and comparison of intersexual power relationships across mammalian societies, perhaps even including humans,” the authors concluded.



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By <a href="mailto:andrei.ionescu5891@gmail.com">Andrei Ionescu</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer

Power between the sexes has not been properly quantified

Social power among animal species has usually been characterized as...

Strong friendships between males aren’t very common in the animal kingdom. Instead, males typically compete among themselves for access to females. In some special circumstances though, male friendships can help with <a href="https://www.earth.com/news/gut-molecule-makes-animals-switch-from-eating-to-mating/">mating</a> success. In fact, some manakins depend on males working together to attract females with elaborate cooperative mating displays.&nbsp;



Among other animals, such as baboons, male friends can help each other rise in social status or defend females from another male, which promotes mating success.&nbsp;



Now, researchers from the <a href="https://www.dpz.eu/en/home.html">German Primate Center (DPZ) Leibniz Institute for Primate Research</a> looked into the benefits of male friendships among wild Guinea baboons in Senegal. These baboons are known for strong male social bonds but lack of a clear male hierarchy.



Among these baboons, the core social groups are made of one male with one to six females and their offspring, with the male typically fathering all of the offspring. The females choose a male freely and stay with him for a few weeks to several years. There are also bachelor males who are not usually sexually active. Several of these core groups along with bachelor males make up a “gang” of baboons.&nbsp;&nbsp;



The scientists wanted to know if male baboons with more friends attracted more females due to the possibility of greater levels of protection for the females and their offspring. Contrary to the hypothesis, males with more friends were not more attractive.&nbsp;



The study revealed that males also spent less time with their male friends once they started spending time with a female and especially when they fathered offspring. Males still maintained some friendships, but just adjusted the amount of time they spent with those friends.&nbsp;



To carry out the research, Federica Dal Pesco and her colleagues collected four years of field data. The experts observed the behavior of 30 males and determined paternity of 50 young.&nbsp;



"Contrary to our predictions, we found no evidence that male-male sociality was linked to higher reproductive success. Instead, we observed a strong negative relationship between bond strength and male reproductive success (i.e. number of associated females and paternities)," explained the study authors. "Guinea baboon males that were associated with a higher number of females spent less time affiliating with other males.&nbsp;



"While a number of now classic studies reported a positive relationship between sociality and reproductive success in both males and females across several mammalian and bird species, our results indicate that male-male sociality need not directly translate into increased short-term reproductive success. Instead, males that invest time and energy in relationships with females, at the expense of relationships with males, have the highest reproductive success."



The study is published in the journal <a href="https://royalsocietypublishing.org/journal/rspb">Proceedings of the Royal Society B</a>.&nbsp;&nbsp;



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By <a href="mailto:zachfitzner@yahoo.com">Zach Fitzner</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer

Male baboons invest more time in relationships with females

Strong friendships between males aren’t very common in the animal...

<a href="https://www.earth.com/news/hummingbirds-cannot-maintain-an-energetic-lifestyle-at-high-altitudes/">Birds</a> that hunt their prey during the night need special adaptations in order to allow them to see in low light conditions and to judge the distance to obstacles in their flight path as well as the distance to their prey. Although these adaptations have been relatively well studied in nocturnal birds such as owls and nightjars, they have not been investigated in the world’s only nocturnal hawk, the letter-winged kite (Elanus scriptus).



Although some species of hawks (Accipitriformes) and falcons (Falconiformes) can hunt at dusk, the letter-winged kite is the only species that is primarily active at dusk and at night. It inhabits the arid central regions of Australia, avoiding settled areas and towns. This habitat preference, along with the species’ nocturnal activity pattern and nomadic movements, makes&nbsp;E. scriptus&nbsp;rather difficult to observe in the wild.



In the past, there has been speculation that the species is more like an owl than a hawk because it appears to have unusually large eyes that face forwards. Some have suggested that the soft tissues of the eyes resemble those of nocturnal birds more than diurnal species, including the other Australian Elanus species, the black-shouldered kite (Elanus axillaris).&nbsp;



Birds that hunt their prey during the night often show specialized adaptations to their visual systems and skeletons. These anatomical changes include large orbits to accommodate eyes with large retinas that contain many photoreceptors. The eye of a nocturnal raptor also usually has a relatively small optic foramen, the hole in the skull through which the optic nerve travels to the brain. Certain areas of the brain of a nocturnal raptor may also be enlarged to facilitate detailed processing and interpretation of the images received by the eyes.



An international study led by <a href="https://www.flinders.edu.au/">Flinders University</a> has now tested the speculation about the letter-winged kite’s adaptations using computed tomography (CT) scanning techniques to obtain high-resolution images from three specimens, along with 27 other raptor skulls. The skulls, all of which were sourced from museums within Australia, came from 16 raptor species in total, 12 of which belong to the Accipitriformes (hawks, eagles and kites) and the remaining three to the Falconiformes (falcons). The images were used to measure and compare eye socket characteristics, such as the orbit diameter and the optic foramen diameter.&nbsp;



“Letter-winged kites hunt at night and must be able to navigate obstacles in the dark while tracking down their favorite prey, the long-tailed rat,” said Professor Vera Weisbecker. “It has therefore long been speculated that their visual system shows adaptations for seeing in the dark, and particularly that they are similar to owls in having larger eyes than other hawks, and larger image processing centers in the brain.”



Dr. Karine Mardon is an experts in The National Imaging Facility at the University of Queensland Centre for Advanced Imaging. Dr. Mardon scanned the skulls of the birds of prey included in the study, and the researchers then compared 3D reconstructions of the letter-winged kite skulls and brains with those of the other birds of prey.



The results of the analysis revealed that things are not as clear as night and day. There was no difference in the relationship between the orbit and optic foramen diameters for the nocturnal&nbsp;letter-winged kite and its diurnal congeners, the black-winged kite (Elanus caeruleus) and the black-shouldered kite (Elanus axillaris). Elanine kites, as a whole, seem to have relatively large orbit diameters, but relatively small optic foramina compared to other species.



“Contrary to many anecdotal reports, the dimensions of the eye of letter-winged kites were no different to two closely related kites from the same genus – the black-shouldered and the black-winged kites,” said study lead author Aubrey Keirnan, a PhD student in Dr. Weisbecker's lab.



“But there was a twist in the story: we realized that all three kite species had larger orbits relative to their optic foramen, the hole in the back of orbit that the optic nerve passes through. This is often seen in nocturnal birds, where a small number of nerves relay a lot of input from the eye into a high-contrast, low-resolution image.”



“This suggests all&nbsp;Elanus&nbsp;kites may be pretty good at seeing in the dark and not too good at seeing in daylight – but for some reason, only the letter-winged kite has made the move into a nocturnal lifestyle."



According to Dr Weisbecker, this might also explain many reports that the letter-winged kite is particularly active during moonlit nights: “It might not actually be very good at flying in the total dark, unlike many owls.”



The study was co-led by Dr. Andrew Iwaniuk from the University of Lethbridge in Canada. He noted that the use of anatomical observations to infer the species’ behavior was an innovative approach to understanding a bird that is notoriously difficult to observe in the wild.



“The species lives in remote, arid Australia, avoids human settlements and is highly elusive. Population estimates vary between 670 and 6,700 individuals according to the IUCN, and it is currently listed as near-threatened. To conserve the species, it is critical that we understand its behavioral needs and capabilities, but they are extremely difficult to observe," said Dr. Iwaniuk.



“We are extremely lucky to have Australia’s amazing museum collections at our disposal to help us understand this bird without the need to find and disturb the species. For example, the letter-winged kite, and its relatives, might be impacted differently by artificial light sources than other hawks."



Dr. Jeroen Smaers of Stony Brook University said the research perfectly exemplifies how studying variation across many species enlightens our understanding of individual species - an approach that is starting to show its contributions to animal conservation.



“Our work on the letter-winged kite is really just the beginning," said Keirnan. "Our measurements showed that many other birds of prey are quite unique in one aspect or other of their visual system. I am excited to spend my PhD on delving further into how measurement of the visual system can help in the understanding and management of other birds.”



The study is published in the journal <a href="https://royalsocietypublishing.org/doi/10.1098/rsos.220135">Royal Society Open Science</a>.



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By <a href="mailto:bosman@truewan.co.za">Alison Bosman</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer

The world’s only nocturnal hawk may not see well in the dark

Birds that hunt their prey during the night need special...

Tree hyraxes are non-descript, mid-sized <a href="https://www.earth.com/news/mammals-change-their-schedules-to-adapt-to-city-life/">mammals</a> that wake after dark in the canopies of Tropical African forests. Because they’re a shy nocturnal mammal living high in trees, little has been discovered about their behavior.&nbsp;



Now, experts at the <a href="https://www.helsinki.fi/en">University of Helsinki</a> are using new techniques to try and understand tree hyrax behavior in the Taita Hills of Kenya.&nbsp;



"Many aspects of tree hyrax ecology remain very poorly known. They are known to mainly feed on leaves of woody plants," wrote the study authors.&nbsp; "Tree hyraxes thus depend on trees for food, but they also utilize den trees for shelter, and dense canopy also allows easy movement between trees."&nbsp;



"Tree hyraxes are thought to be mainly solitary animals that maintain social relationships by calling and scent-marking signals. They are highly vocal and calling seems to be their primary means of communication."



Using thermal imaging cameras, the researchers were able to observe hyrax social behavior - something never before seen. The study also revealed what plants they especially enjoyed eating and where they hid for shelter.



In addition to thermal imaging cameras, automated acoustic recorders captured hyrax vocalizations. Besides being able to record data on interactions between the animals, these recordings allowed scientists to estimate a population for the first time.&nbsp;&nbsp;&nbsp;



“In small forest patches, the calls of tree hyraxes were rarely heard, and only in the early hours of the morning. These few surviving animals are making every effort to avoid detection and the attention of potential poachers,” said Hanna Rosti, who has long studied tree hyraxes.



Armed with their new data, the scientists estimate that there are only 2,000 to 4,000 hyraxes in the Taita Hills area where they conducted their research. This information is important for conservation of the hyrax. The scientists hope that the study will also have positive implications for tree hyraxes throughout Africa.&nbsp;&nbsp;&nbsp;



“The results acquired through this research will move tree hyrax conservation significantly forward, not only in Taita Hills but also in other parts of Africa," said Professor Jouko Rikkinen.



"The methods used can also be applied to other nocturnal animals that are difficult to get close to."



The study is published in the journal <a href="https://www.nature.com/srep/">Scientific Reports</a>.



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By <a href="mailto:zachfitzner@yahoo.com">Zach Fitzner</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer

New clues about the secretive lives of tree hyraxes

Tree hyraxes are non-descript, mid-sized mammals that wake after dark...

While millions of years ago, all mammals lived on land, at one point, some species such as seals and whales left land and evolved to live in the sea. Since underwater, <a href="https://www.earth.com/news/new-device-identifies-mosquitoes-using-only-sound/">sound</a> is a more reliable sensory cue than vision, it is not surprising that aquatic species have developed auditory organs that are more efficient in processing underwater sounds than the hearing apparatuses of terrestrial mammals, including humans.&nbsp;Surprisingly though, a new study led by the <a href="https://www.sdu.dk/en">University of Southern Denmark</a> has found that, in some cases, humans can hear as well as seals underwater.&nbsp;



Since the 1950s, scientists have made various attempts to measure human hearing underwater. The U.S. Military, for instance, had an interest in understanding how divers are affected by underwater explosions, so they directed a significant amount of funding to clarify this issue. However, subjects were generally tested with diving equipment on, including neoprene caps or air-filled diving masks, which can affect their hearing.&nbsp;



“Common to all these scientific studies is that they all find hearing thresholds [the sound levels below which the auditory system is unable to detect any sound] that are higher than the thresholds we have found in our new study,” said study co-author Jakob Christensen-Dalsgaard, an expert in animal hearing at SDU.



By measuring the underwater hearing thresholds of seven participants, the experts found that the average threshold was 71 dB at a frequency of 500 Hz.&nbsp;



“It is 26 dB lower than hypothesized in previous studies, so we must conclude that humans hear significantly better underwater than previously reported by science. In fact, the threshold at 500 Hz is in line with how well animals such as cormorants and seals hear underwater,” said&nbsp; Dr. Christensen-Dalsgaard.



While previous studies hypothesized that human hearing underwater is mediated by bone conduction, with sound waves causing vibrations in the skull, this new study argues that resonance in the enclosed air in the middle ear actually amplifies the sound and makes the ear more sensitive – a phenomenon common to cormorants, turtles, and frogs too.



However, the sense of hearing is not only about being able to pick up sounds, but also about determining the direction of the sound – which, for humans, remains very difficult underwater.&nbsp;



“In air we can determine the sound direction within a few degrees, but in water there is an up to 90 degrees error margin. This is not so strange, because we are trained to react to the small time differences between the ears, which are due to the speed of sound in air. In water, the speed of sound is four times greater, and the time differences are much smaller,” explained Dr. Christensen-Dalsgaard.&nbsp;



“The results tell us that humans have a reduced ability to determine the direction of sounds underwater, thus confirming that human hearing is not adapted to work well underwater,” he concluded.



The study is published in the journal <a href="http://dx.doi.org/10.1016/j.heares.2022.108484">Hearing Research</a>.&nbsp; &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;



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By <a href="mailto:andrei.ionescu5891@gmail.com">Andrei Ionescu</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer

Can humans hear as well as seals underwater?

While millions of years ago, all mammals lived on land,...

As global warming brings higher temperatures to <a href="https://www.earth.com/news/how-does-extreme-weather-impact-marine-ecosystems/">ecosystems</a> around the world, it is likely that some animal species will need to move to cooler areas in order to remain functional. This could mean moving towards higher latitudes or towards higher altitudes. The problem with moving up a mountain side, however, is that it brings a decrease in oxygen availability along with the cooler temperatures. For animals with high metabolic rates, such as hummingbirds, this combination of factors may make life at high altitudes impossible.



To find out what the impact of higher altitude living is on Anna’s hummingbirds (Calypte anna), Austin Spence from the University of Connecticut, USA, and Morgan Tingley from the University of California, Los Angeles, USA, transported some of these birds to sites at various heights up mountainsides. The birds occur naturally over a range of altitudes, from sea level to around 2,800 meters, so the researchers predicted that the birds would show a range of adaptations to living at altitude, and that those already comfortable at 2,400 meters would cope better when transported to 3,800 meters.



Using net traps, the researchers trapped hummingbirds from sites of different altitudes ranging from 10 metersabove sea level (Sacramento, CA) up to 2,400 meters (Mammoth Lakes, CA).&nbsp; Spence and team member Hannah LeWinter of Humboldt State University then transported the birds to an aviary in western California at an altitude of 1,215 meters. The birds were given a few days to acclimatize in these new conditions.



The scientists then measured their oxygen consumption by enticing each bird to insert its head into a tiny funnel to sip a sugary solution. The consumption of O2 indicates metabolic rate since oxygen is used to produce the energy that is used during metabolism. Spence and LeWinter also measured each hummingbird’s carbon dioxide (CO2)&nbsp;production overnight, which is also a measure of metabolic rate.&nbsp;



After collecting this data, the birds were moved again, this time to aviaries at a nearby research station close to the peak of Mount Barcroft, CA, which is at an altitude of 3,800 meters. At this site there is around 39 percent less oxygen in the air and the ambient temperatures are around 5°C lower. After acclimatizing for four days, the birds’ metabolic rates were again measured while they hovered and while they slept.&nbsp;



Their results, published today in the <a href="https://journals.biologists.com/jeb/article/225/10/jeb243294/275376/Anna-s-hummingbird-Calypte-anna-physiological">Journal of Experimental Biology</a>, show that the hummingbirds exhibit a 37 percent decrease in metabolic rate at an altitude of 3,800 meters. Instead of working harder to hover in the thin air, 1,000 meters above their natural range, the birds suffered a large drop in their metabolic rates. And the energy used by birds that had originated at higher altitudes was no different from the energy used by those that had lived close to sea level – they all struggled equally on the mountain top.&nbsp;



“Overall, these results suggest low air pressure and oxygen availability may reduce hovering performance in hummingbirds, when exposed to the acute challenge of high-elevation conditions,” explained Spence.&nbsp;&nbsp;



In addition, the birds fell into a state of deep torpor each night, when they slept. This is a form of overnight hibernation, where the metabolic rate is lowered significantly in order to conserve energy. Although the birds showed this behavior at the lower experimental altitude (1,215 meters), it was more extreme in the colder conditions at 3,800 meters. Here they were torpid for more than 87.5 percent of the chilly, high-altitude night.



“It means that even if they’re from a warm or cool spot, they use torpor when its super-cold, which is cool,” said Spence.&nbsp;



The researchers hypothesized that hummingbirds originally from higher altitude habitats may have larger lungs to compensate for the lower oxygen availability in the air at those sites, but this was not so. However, these birds did have larger hearts, which would help to circulate oxygen more rapidly around their bodies.&nbsp;



Unfortunately, the results from this experimental research indicate that hummingbirds will probably not be able to relocate up mountainsides to find more suitable environments as climate change makes conditions uncomfortable for them.&nbsp;



“Our results suggest lower oxygen availability and low air pressure may be difficult challenges to overcome for hummingbirds,” said Spence, meaning that the birds will instead have to shift northward or southward in search of cooler climes.



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By <a href="mailto:bosman@truewan.co.za">Alison Bosman</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer

Hummingbirds cannot maintain an energetic lifestyle at high altitudes

As global warming brings higher temperatures to ecosystems around the...

Offshore wind farms generate much-needed renewable energy that is environmentally friendly and cost-efficient. In the early stages of construction, there is usually noise and disturbance as the turbines are erected, but this is well regulated and of short duration. After completion, the only disturbance that remains is due to the low-level sound emissions of the turbines. But this constant noise pollution may have an impact on marine <a href="https://www.earth.com/news/greater-risk-of-extinction-for-large-bodied-mammals-in-the-past/">mammals</a> that produce their own sounds in order to communicate with one another.



At the 182nd Meeting of the <a href="https://acousticalsociety.org/">Acoustical Society of America</a>, to be held at the Sheraton Denver Downtown Hotel this week, Frank Thomsen of DHI will discuss how this constant noise may impact marine wildlife. His presentation is titled “Operational underwater sound from future offshore wind turbines can affect the behavior of marine mammals,” and it will take place on May 26.



He will report on research that he and his colleagues did by reviewing published studies on the sound levels emanating from operational wind farms. They were interested in the effects of turbine size on noise emissions and found that, in general, larger turbines produced higher levels of noise. The long-term consequences of this noise on marine wildlife are largely unknown, but it is hypothesized that constant background noise can interfere with the communication patterns and behavior of mammals at sea.&nbsp;



However, turbine size is not the only important factor to consider. The disruptive impact may also be influenced by the number of turbines and the ways in which their sound patterns overlap. In addition, the gearbox technology used in older turbines produces disruptive nose for a distance of up to 6.3 kilometers while newer, direct-drive turbines may only affect animal behavior within a 1.4-kilometer radius.&nbsp;



“It is very unlikely that operational noise will lead to any injury or even hearing impairment, but behavioral changes could be a concern, as our study shows,” Thomsen said. “It's possible that impact zones of individual turbines overlap, but that still does not mean that the wind farm is a no-go area for marine life. We see harbor porpoises frequently swimming in the vicinity of turbines.”



In theory, the underwater sound could lead to behavior changes in marine mammals and mask calls from whales, but harbor porpoises are frequently seen swimming in the vicinity of wind farms in Europe, so it may not be as simple as it seems.



“Since offshore wind farms have a relatively long lifespan, and there will be many of them, the potential impacts should not be overlooked,” said Thomsen. “The point of our work is to raise awareness.”



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By <a href="mailto:bosman@truewan.co.za">Alison Bosman</a>, <a href="https://www.earth.com/staff/">Earth.com</a> Staff Writer

Noise from wind farms could affect marine mammal behavior

Offshore wind farms generate much-needed renewable energy that is environmentally...

Cryptolestes dissimulatus

Taxonomic tree: