Scientists use forensic technology to genetically document infanticide in brown bears

Modern open-source software helped the researchers identify the male that killed a female and her two cubs

Scientists used a technology designed for the purposes of human forensics, to provide the first genetically documented case of infanticide in brown bears, following the murder of a female and her two cubs in Trentino, the Italian Alps, where a small re-introduced population has been genetically monitored for already 20 years.

The study, conducted and authored by Francesca Davoli, The Italian Institute for Environmental Protection and Research (ISPRA), Bologna, and her team, is published in the open access journal Nature Conservation.

To secure their own reproduction, males of some social mammalian species, such as lions and bears, exhibit infanticidal behaviour where they kill the offspring of their competitors, so that they can mate with the females which become fertile again soon after they lose their cubs. However, sometimes females are also killed while trying to protect their young, resulting in a survival threat to small populations and endangered species.

“In isolated populations with a small number of reproductive adults, sexually selected infanticide can negatively impact the long-term conservation of the species, especially in the case where the female is killed while protecting her cubs,” point out the researchers.

“Taking this into account, the genetic identification of the perpetrators could give concrete indications for the management of small populations, for example, placing radio-collars on infanticidal males to track them,” they add. “Nevertheless, genetic studies for identifying infanticidal males have received little attention.”

Thanks to a database containing the genotypes of all bears known to inhabit the study site and an open-source software used to analyse human forensic genetic profiles, the scientists were able to solve the case much like in a television crime series.

orsa occultata - leggeraUpon finding the three corpses, the researchers were certain that the animals had not been killed by a human. In the beginning, the suspects were all male brown bears reported from the area in 2015.

Hoping to isolate the DNA of the perpetrator, the researchers collected three samples of hairs and swabbed the female’s wounds in search for saliva. Dealing with a relatively small population, the scientists expected that the animals would share a genotype to an extent, meaning they needed plenty of samples.

However, while the DNA retrieved from the saliva swabs did point to an adult male, at first glance it seemed that it belonged to the cubs’ father. Later, the scientists puzzled out that the attacker must have injured the cubs and the mother alternately, thus spreading blood containing the inherited genetic material from the father bear. Previous knowledge also excluded the father, since there are no known cases of male bears killing their offspring. In fact, they seem to distinguish their own younglings, even though they most likely recognise the mother.

To successfully determine the attacker, the scientists had to use the very small amount of genetic material from the saliva swabs they managed to collect and conduct a highly sophisticated analysis, in order to obtain four genetic profiles largely overlapping with each other. Then, they compared them against each of the males reported from the area that year. Eventually, they narrowed down the options to an individual listed as M7.

“The monitoring of litters is a fundamental tool for the management of bear populations: it has allowed the authors to genetically confirm the existence of cases of infanticide and in the future may facilitate the retrieval of information necessary to assess the impact of SSI on demographic trends,” conclude the researchers.

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Original source:

Davoli F, Cozzo M, Angeli F, Groff C, Randi E (2018) Infanticide in brown bear: a case-study in the Italian Alps – Genetic identification of perpetrator and implications in small populations. Nature Conservation 25: 55-75. https://doi.org/10.3897/natureconservation.25.23776

Do squirrels teach bears to cross the railroad? Grizzlies dig squirrel middens for grains

Grains have been reported to regularly trickle from hopper cars travelling via the railway located within the Canadian Banff and Yoho National Parks, attracting the local red squirrels.

As a result, the rodents have grown used to foraging on the spilled seeds, which they collect in underground storage areas where they can be discovered and dug up by grizzly bears. Grain-conditioned bears may frequent the railway more often than usual, resulting in increased mortality by trains strikes.

Furthermore, the dispersal, following caching and digestion of such seeds by both squirrels and bears, could lead to the spread and establishment of those agricultural plants in the area.

Figure1B

The case is investigated and discussed by members of the University of Alberta‘s research team of Julia Elizabeth Put, Laurens Put and Dr. Colleen Cassady St. Clair. Their study is published in the open access journal Nature Conservation.

It all began when members of the team found a grain-filled midden that was visited by a bear near where the same bear had bluff-charged Parks Canada employees. At the time, the researchers were investigating possible explanations for causes of grizzly bear mortality on the adjacent railway. Thus, an unexpected opportunity to document interactions between species and how those can lead to human-wildlife conflicts presented itself to the scientists.

The three basic questions brought up by Julia and her team were whether spilled grain could increase the number of squirrels near the rail; if other middens contained grain; and if other bears accessed grain in middens. Eventually, their data provided a resounding ‘yes’ to all of them.

In some mountain parks in North America, including Banff, grizzly bears are known to excavate squirrel middens to access whitebark pine seeds. The tree, however, is only found at high elevations far from the valley bottom where the railway is located. Nevertheless, this behaviour may easily translate to targeting other food items in middens, such as grain, speculate the researchers.

Once a bear consumes grain from a squirrel midden, it could initiate or reinforce a tendency to seek grain on the rail, where it is generally less concentrated. Such conditioning of food rewards could lead to grizzly bears spending more time in the area around or on the rails, where they would be at risk of being struck by trains.

“The only feasible mitigation for these effects is to reduce spillage from hopper cars via careful attention to loading and gate maintenance,” conclude the authors.

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Original source:

Put JE, Put L, St. Clair CC (2017) Caching behaviour by red squirrels may contribute to food conditioning of grizzly bears. Nature Conservation 21: 1-14. https://doi.org/10.3897/natureconservation.21.12429

How bears bulk up ahead of the summer: A study into the Asiatic black bear’s spring diet

Much like gym enthusiasts, every year Asiatic black bears seem to be on the lookout for protein-rich food ahead of the summer, so that they can bulk up on lean muscle mass in place of the fat tissue formed last year prior to hibernation. This was concluded in a study by Dr. Shino Furusaka, Tokyo University of Agriculture and Technology and his team, based on direct observations on bears living across an area of about 60 km2 in Japan. The study is published in the open access journal ZooKeys.

In order to determine the bears’ food preferences and habits, the scientists followed a large number of animals in the Ashio area of the Ashio-Nikko Mountains in Japan from April to July in both 2013 and 2014. To avoid unnecessary intrusion, they stayed at a distance of at least 200 metres using video cameras with telescopic lenses to document the sightings. Having documented the plant species the bears consumed, the researchers studied their nutritional content and made conclusions about the nutrients needed for the species after hibernation.

While heavily dependent on food availability, generally the bears were noted to prefer food which is high in protein, but poor in fibre — likely because their stomachs and intestines were unable to efficiently digest the latter. Furthermore, the protein-rich diet ensures that the muscle mass is rebuilt to replace the lost winter fat.

Interestingly, the bears were observed to change their food preferences as spring progressed and that seemed to be linked to the shifts in the nutritional value of the available food.

Starting with their observations at the beginning of April, the scientists did not record any feeding behaviour until the end of the month. As leaf flush was yet to occur, the animals were active and feeding on overwintered grass. However, in early May, the bears began consuming newly emerged leaves, grass and, later in the month, they added flowers to their menu.

A shift in behaviour occurred in the following months. In June and July, the bears were seen to feed mainly on ants, with a small portion of their food intake consisting of grasses, sika deer carcasses and bees. Curiously, when the scientists looked into the nutritional content of the same plants which the animals sought only a few weeks ago, they found out that now they were significantly poorer in protein and richer in fibre.

Another finding showed that the calories in the different items were not related to the choice of food which likely proves that the key factor is none other than the amount of protein, provided that the fibre value is low enough for good digestibility.

Understanding the food preferences and habits of animals, as well as the reasons behind them, is essential for the development and revision of habitat management plans. However, previous knowledge of the feeding behaviour of Asiatic black bears has been based solely on faecal analyses which has not provided sufficient details on which nutritional factors influence the use of particular foods.

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Original source:

Furusaka S, Kozakai C, Nemoto Y, Umemura Y, Naganuma T, Yamazaki K, Koike S (2017) The selection by the Asiatic black bear (Ursus thibetanus) of spring plant food items according to their nutritional values. ZooKeys 672: 121-133. https://doi.org/10.3897/zookeys.672.10078