How Having a Family Improves Digestion in Social Geese

As a human being, having family and friends helps us in many ways. Animal societies are not much different: a stable social environment is essential for the health of the body. Among birds, graylag geese are highly social. Therefore, they are a very good example for studying the benefits of living in groups. In this study, we looked at the quality of the digestion and the breeding success of 38 free-living graylag geese. The birds were individually tagged and belonged to different social categories. The categories were pairs with offspring, pairs without offspring, and unpaired birds. We found that individuals that have stable social relationships with their family members have better digestion and are more likely to breed successfully in the following breeding season. These are new insights into the benefits of social life in birds.

If so, then your health has probably benefited from being in a family. You and the rest of your family benefit nutritionally from the care you give each other. It turns out that the same thing happens in animal families and/or societies, where the social position of an individual animal a ects its life in many ways. For instance, whether an animal has a mate or not may influence how much power it has within the group. Additionally, the social position of an individual within the group a ects its behavior when feeding and therefore how much and what kind of food it gets to eat [ ]. Generally, the dominant individuals in a group are faster at getting access to food and more motivated to defend food resources as compared to low-ranking individuals. This means that high-ranking individuals in the group have access to larger quantities of food, which is often of high quality, too. In addition, a high rank is often linked to better reproduction, lower stress [ ], and good digestion [ ].
Among birds, graylag geese (Anser anser) are highly social. These geese have been extensively studied and are an ideal species to use for research about social interactions in animals. They live in big flocks for most of the year and pair-partners (male and female) usually stay together for several years, similar to the way humans form couples. Paired birds often stay close to each other during the day no matter what they are doing, for example feeding or resting. After short separations, or simply when they get excited (when other geese are fighting, for example) they greet each other to show that they belong together. Furthermore, graylag geese have strong family ties. Goslings, which are young geese, stay close to their parents from hatching until the next breeding season, which means at least year.
As in human society, disputes between pairs, families, and clans are common within flocks. Conflicts produce social instability and stress. However, a so-called social partner, which could be a mate, one of the parents, or a sibling, can reduce the stress caused by disputes in the social environment and improve the well-being of an individual. To investigate the relationship between the social environment and an individual's well-being, we looked at digestive e ciency. This

DIGESTIVE EFFICIENCY
The proportion of eaten food that gets broken down for use by the body. measurement tells us how much of the food that was eaten was broken down for use by the body. We expected social relationships to a ect digestive e ciency in graylag geese.

WHAT DID WE INVESTIGATE?
We studied a group of graylag geese to find out if and how digestive e ciency and social environment, such as being paired or not, or having o spring or not, are related to each other. The study was conducted in February, when the ground was fully covered with snow and the geese were only able to feed on the food we provided. In this way, we regulated the quantity and quality of the food available.

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October | Volume | Article | First, we hypothesized that paired birds with o spring would have a better digestive e ciency than unpaired individuals. We considered the digestive e ciency to be an indicator of nutrition and therefore also of the overall body condition of an individual. At the end of winter, when these data were collected and the breeding season starts, an individual's body condition will play a major role with respect to reproduction. Animals with healthy bodies will be more likely to have o spring. Therefore, as a second hypothesis, we expected digestive e ciency to be related to breeding success.

BREEDING SUCCESS
The number of hatched eggs.

WHERE ARE THE BIRDS WE STUDIED?
The study was conducted at the Konrad Lorenz Research Center in https://klf.univie.ac.at/ the valley of the river Alm in the northern part of the Austrian Alps, which are located in central Europe. A non-migratory flock of graylag geese was introduced there by Konrad Lorenz in . The birds are free to move and fly around and generally spend their time close to the research center, where they are provided with food twice a day, all year round. All geese are tagged with colored rings on their legs and are used to the close presence of humans. Data about every individual goose has been collected since , and therefore we know the friends and relatives of each bird in the flock.

HOW DID WE STUDY DIGESTIVE EFFICIENCY IN GEESE?
During the period of data collection, the flock consisted of individuals. Droppings from individuals ( males and females)

DROPPINGS
The equivalent of feces and urine in mammals.
In birds, they are eliminated together in the droppings.
belonging to di erent social categories within the flock (paired with and without o spring, unpaired individuals, and juveniles) were collected during consecutive days in winter . During this period, the snowpack forced the birds to feed exclusively on the pellets we provided, which were made out of a mix of cereals, dried herbs, and grasses. In sum, droppings were collected immediately after defecation (pooping) and were frozen at − • C within h, until DEFECATION A nice way of saying "going poop." further analysis.
To find out how e ciently the geese digested their food, both the food pellets and the droppings were analyzed by drying them in ovens and a test was performed to determine how much lignin was in them. Lignin is an indigestible plant component. Since lignin cannot be digested, it can be used as a natural marker providing information about the quantity of food ingested, assimilated and ejected (Figure ). We then calculated the digestive e ciency of the geese using this equation

MEAN?
As expected, our results showed that social environment fine-tunes digestive e ciency. Paired individuals with o spring showed better digestive e ciency than paired individuals without o spring or unpaired birds (Figure ). Additionally, the results suggest that individuals with stable social relationships had better digestive e ciency. We think that pairs with o spring benefit because the juveniles also help to look out for potential challenges, allowing the parents (or the entire family) to spend more time feeding. It is known from other goose species that long-lasting family ties are beneficial for both o spring and parents. For instance, young barnacle geese living in family units were less disturbed during feeding than those who had left the family unit [ ]. The juveniles considered in our study were already years of age and were no longer spending time with their parents. Nevertheless, they had a high digestive e ciency, which suggests that other factors are involved in the relationship between social environment and digestive e ciency. For instance, juvenile graylag geese may be comparable to adolescent humans, who are hungry all the time and do not really get fat, because they e ciently direct their food resources into growth.
Our study also showed that geese that hatched o spring in the breeding season following the data collection period showed higher digestive e ciency than those failing to hatch goslings (Figure ). The egg-laying period, which starts at the end of winter, is energetically very demanding. Just consider that a female goose weighs ∼ kg, one goose egg weighs ∼ g and a female lays on average six eggs, which means about kg of her body mass. Therefore, it might be essential for a goose, at the beginning of the breeding season, to be e cient in digesting food, to provide enough energy to lay eggs. However, we are still not sure if there is a direct cause/e ect relationship between kids.frontiersin.org October | Volume | Article |

Figure Figure
Di erences in percentages of digestive e ciency between geese from di erent social categories. You can see that paired individuals with o spring showed better digestive e ciency than paired individuals without o spring or unpaired birds. The results suggest that individuals with stable social relationships had better digestive e ciency.

Figure
Di erences in percentages of digestive e ciency between individuals with hatchlings and those without in the season following the study. You can see that geese that individual with hatched o spring in the breeding season following the period of data collection showed higher digestive e ciency than those failing to hatch goslings. This suggests that it might be important for a goose to be able to digest food e ciently at the beginning of the breeding season in order to store su cient energy for egg laying.
digestive e ciency and reproductive success. To find this out, further experimental studies would be needed. So now you know that digestive e ciency is considered to be an indicator of the overall body condition of an individual. Furthermore, you know that the physical constitution and possibly also the reproductive success of an individual are supported by stable social relationships. This is important for all social animal species because it shows that the social environment may influence an animal's well-being in both the short-and long-term, by a ecting breeding success.  . How having a partner and a family influences the stress response of graylag geese. Front. Young Minds : . doi: . /frym. . . Lima-Ojeda, J, Rupprecht, R., and Baghai, T.
. Wild Goose Dilemmas: Population Consequences of Individual Decisions in Barnacle Geese. Groningen: Branta Press.