Greater Sage-Grouses: Methods of Communication
This essay is going to evaluate methods of communication, explaining how optimal foraging and sexual selection behaviour is influenced in Greater Sage-Grouse (Centrocercus urophasianus) (IUCN Red List, 2016). Males have a grey crown and white around their neck whereas females have less white colouring and are much smaller in size. Greater Sage-Grouse are the largest Grouse of North America with a habitat of sagebrush-grasslands and a diet that consists of animals and plants (Storch, 2004).
Animals have a variety of communication methods to show how they are feeling in a certain situation. For example, to warn others of danger, inform others of a good food source, claim territory or to attract a mate (Gillam, 2011). This is done by either tactile, visual, sound or chemical communication. Ethology has shown the different ways in which animals behave and the possible reasons for each. Although some of this behaviour is passed on through genes others are learnt, and this is evolved over generations through natural selection. Each learned behaviour can change dramatically throughout the animal’s lifetime to help them survive (Hosey et al, 2013). In addition, each behaviour has costs and benefits as well as proximate (the immediate response) and ultimate causes (the reasons for the response) and different methods of communication aids in completing a specific end goal (Dickinson et al, 2018).
Animals are heterotrophs and require food for many reasons including fuel and essential nutrients. Greater Sage-Grouse are ground foragers that feed solitary. They are mainly herbivores with a diet consisting of sagebrush, leaves, buds and forbs but they do also feed on insects such as beetles, moths, grasshoppers and ants (Dahlgren et al, 2015). However, this changes depending on the season and the age of the animal. In winter sagebrush makes up all their diet whereas in spring and summer they will eat shrubs, forbs and insects (Dahlgren et al, 2011). When young they are insectivores, relying just on insects to survive, due to requiring the protein for development and growth. This means that when the female is picking a nesting site, it is important to make sure this food is highly available. If the correct place was not to be chosen then food could be limited which would lead to the female adult having to use up more energy looking for insects, which also exposes the offspring to predators for a longer period of time (Coates et al, 2008). Additionally, if the correct type of food is not provided for the young then this can result to mortality or reduced fitness in adulthood (Beck et al, 2019).
Behavioural responses are generated by natural selection in order to maximise fitness by balancing the benefits with the costs. Each animal is required to decide when and where to forage, the food to feed on, how long to spend foraging in an area and how to get to a new location (Pyke, 2019). When foraging, some of this behaviour is genetics whereas others is learnt by copying the behaviour seen in adults, so they know what to feed on and where to find these resources. The optimal foraging theory (OFT) is the prediction of when an individual would be more beneficial by staying in one area or moving to a new location to feed (Alcock, 2009). By identifying when to move to find food compared to staying in the same area looking then more energy will be gained with the correct choice, helping the individual to survive. The marginal value theorem is when the animal recognises that food is now limited in the area and they will benefit more by moving on (Daw et al, 2016).
The formula that is used as part of the OFT is Pi= Ei/hi Profitability of prey= (energy provided by prey)/(time (hours)required to catch and consume each prey type) (Gustafson, 2019). This calculation shows which prey provides the most energy per hour for the Greater-Sage Grouse. For example, comparing if the individual should eat grasshoppers or beetles. With the assumption that the grasshoppers provide 25kcal but take 30 minutes to catch and consume whereas beetles provide 10kcal but take 15 minutes to catch and consume, the equation can calculate which insect would be more beneficial to the Sage-Grouse. For grasshoppers Pi= 25/0.50 = 50kcal/h and for beetles Pi= 10/0.25 = 40kcal/h. Therefore, this calculation shows that for every grasshopper the Sage-Grouse finds and eats they gain more energy than they would by foraging for beetles.
Furthermore, the formula Pi= Ei/((hi+Si)) Profitability of prey= (energy provided by prey)/((time (hours) required to catch and consume each prey type+search time required to find prey)) is used to assess if an animal will gain more energy and be better off by moving to a new location or staying in the same place and look around for food (Gustafson, 2019). For example, if the grasshopper was to have a search time of 30 minutes and the beetle of 15 minutes the further calculation can be done to show which is the better option. For grasshoppers Pi= 25/((0.50+0.50))= 25 kcal/h and for beetles Pi= 10/((0.25+0.25)) = 20 kcal/h. So, the OFT for this example shows the Greater Sage-Grouse will receive more energy by moving on and looking for grasshoppers in another area than staying in the same location looking for beetles. When hunting, the animals will begin to recognise which food gives them the most energy so overtime they will learn the better option, not wasting time or energy looking for other alternatives.
One way in which Greater Sage-Grouse communicate whilst foraging is visually. Even though they are solitary animals and live alone, only coming together to mate, they will use the presence of each other to determine if an area is suitable to spend time feeding there or not. Many resources, such as food, are required by each individual to survive in the environment they are living in. If there are others of the same species, or those that share the same diet, in a specific area then this indicates a healthy, intact habitat that they will be likely to survive and easily find food (Beck et al, 2012). Therefore, foraging will be successful and no energy would be wasted. Compared to if there was an area with no Grouse then this shows food is scarce here and it would take longer to feed at that location, and they may not be successful with what they find. If they were not to use this method as one way of communicating, then a lot more time and energy would be spent hunting. This could lead to them becoming weak and potential threats, such as predators, would be more of a danger to them with having to spend more time in the open looking for food.
Costs and Benefits
A cost to this method of communication is predator presence. If there are many Grouse feeding in one area, due to there being enough resources, predators such as golden eagles are more likely to feed in that same area too. Therefore, since the Grouse will be distracted in feeding, they may not notice any of these predators around and get eaten themselves. The proximate cause, of them being hungry, can overtake and mean they are less concerned of what is around and are focused just on finding food. However, a benefit to this is a predator is more likely to get noticed when there are more prey in the same area which will warn the others when they attempt to get away. Another cost to this is competition between individuals. By using these methods of finding food, eventually resources will become scarce in the area meaning they will have to move. Even when there is enough food to feed many, they are still competing and some will get pushed out meaning they do not get as much nutrients or energy, making them weaker. Although, this means that with the weaker Grouse around, they are more likely to get into danger allowing the stronger individuals to survive.
Another communication method in which Greater Sage-Grouse use to aid with foraging is sound. Even though they do not vocalise to each other to acknowledge the presence of food, they can use the sound from their predators to stay protected (Burda et al, 2019). Grouse have nest predators, such as magpies and ravens, so they can listen for their callings and know not to forage at this time as if they leave their offspring to find food there will be a high chance of predators taking them. (Blickley et al, 2013).
These methods of communication influences foraging since it will affect the times when the Grouse go out to feed compared to when they remain at the nest and protect their young. If they were not to use the sounds around to help with this then they would not be aware of the potential threats close by, which would lead to the death of many young. Likewise, if they were not using the presence of others of the same species as an indication to food then more energy would be used. This means more time could be spent deviating away from their home range which can open them up to new threats in a new area they are not familiar to. Additionally, this can decrease the population of the species with them being open to the threat of predation for longer periods of time.
Costs and Benefits
A benefit to listening for predators is the distance a call can travel. This means the Grouse do not have to see them to know their presence and can take cover away from them when feeding. However, a cost to relying on hearing before seeing them is the predators may see the Grouse, and their nest site, before they make a sound (Blackwood et al, 2012). Therefore, they would keep quiet sneaking up on the Grouse unexpectedly before they are able to protect themselves or offspring, depending on the predator. Another benefit to this communication method is other sounds, for example additional animals in the area. This could deter the Grouse predators from the route they were going and go a different direction to find other prey they can hear. This would protect the Greater Sage-Grouse in that area and distract the predators from finding them when they are in the open finding food. However, a cost to the background noise is this could lead to the Grouse not hearing the predators. Other noises such as wind and other animals can deter the sound causing mix signals and the Grouse could miss identify a calling, so they would be unaware of the danger around them (Blickley et al, 2013).
All animals need to reproduce in order to pass on genes and to help the population of the species increase. Greater Sage-Grouse are polygyny since the males mate with many females (Koch et al, 2015). The reason for this is so the males pass on their genes to as many offspring as possible. If they were to only mate with one female then all of those young may not survive, whereas by mating with many females there is a higher chance of more individuals surviving therefore more young with the males genetics.
The method in which Greater Sage-Grouse use to find a mate is through lekking. A lek is when a group of males gather in early spring and the females will watch them perform courtship displays to pick a male to mate with (Mcfarland, 2006: page 120). The ‘courtship strut’, which is the display by the species, can be done for hours with a lot of time and energy going into them (Dawkins et al, 2012). Some females can take a long time to decide on a mate and come back for several days to watch the displays before deciding. At this lekking area only copulation occurs here, then the female leaves to nest and rear her offspring alone. The males only contribution during this is his genetics, no help with bringing up the young is provided (Alcock, 2009). The function of this strategy is to bring the same animal of both sexes together in the same area to reproduce and pass on genes. However, not all individuals will pass on their traits as only the ones that make the best impression, with the bigger feathers and larger air sacs as well as with the best displays, will be chosen as they are showing a more dominant presence. Therefore, the individuals with smaller features will not get picked over those leaving them with no or little offspring, so none of their genes will be passed on.
Grouse are oviparous animals meaning they produce offspring by laying eggs (Bentley et al, 2011). Despite many game birds being an r selected species, Greater Sage-Grouse have more of a k selected strategy. This is due to them having a relatively low clutch size of 4 – 9 eggs and a longer lifespan, compared to other birds, of 4 – 6 years (Connelly et al, 2011). This small amount of offspring is beneficial to the female Grouse since they have to rear them alone and have no help from the males. However, it does mean if some die then there are not many to rely on for survival.
The hot shot and hot spot hypothesis are two suggestions as to how the Grouse pick their lekking site. The hot shot suggests that the females prefer more attractive males. Therefore, the unattractive individuals will join those with better features in the hope that will attract more females, increasing their chances of getting noticed. This is an example of dishonest communication since they are trying to convince the females they have more desirable traits than they do. However, the hot spot hypothesis is that males gather where they are more likely to come across many females. This would increase their chances of getting noticed by the females and therefore mating, due to the amount present in the area that will see their display (Blake et al, 2007).
During the lek one way in which they communicate is visually. To get the attention of a female Greater Sage-Grouse the male will open its tail feathers, puff their chest, and strut around in the aim to get noticed (Dawkins et al, 2012). During this, the sender (the male Grouse) sends a signal (the courtship strut) that they are ready to mate to the receiver (the female Grouse) via the air in a courtship context. This is an example of honest behaviour as they do want to mate with the females (Bradbury et al, 2019). In order to achieve this the males will choose a site that is open, with very little vegetation, so there are no obstructions to stop the females from watching the display. Visual communication influences sexual selection because only the individuals that are seen as the strongest will get picked by the females. Therefore, little genes from weaker Grouse will get passed on, since they will not get picked for a mate as often, which will affect the population rate and help them with survival.
Costs and Benefits
A cost to this method of communication is a lot of time and energy is spent on the displays. However, the benefit to it is if they do get picked then their genes will be passed on to many offspring (Alcock, 2009). Also, this way of communicating can increase the predation rate. This is due to the amount of Greater Sage-Grouse present at one lekking site so it is easier to be spotted. In addition, each male will be more focused on the display and trying to get the attention of the females. This will distract them from the environment so any predators could go unmissed, until it is too late to take cover and escape from them (Nordell et al, 2017). Although, the benefit to having many individuals is if there are predators present the weaker Grouse are more likely to get caught, allowing the stronger and fitter ones to escape and survive. Even though this behaviour will cause competition for a mate and a lot of energy will be spent in the displays, weaker individuals will be driven away from exhaustion. This means that when the females are watching they will see which are the strongest. Therefore, due to natural selection the genes of the stronger Grouse will be passed on, helping future generations to survive.
There are vocal elements as part of the courtship strut too. The male inflates and then suddenly deflates two large air sacs on his chest, found under his neck and breast feathers, creating two sharp pops and swishing sounds which can be heard over a kilometre away (Goller et al, 2009).
This communication method is used by the males to enable the females to locate them at a lek. If the females did not react to the noises, then they would not be able to find the lekking site as easy as they do. They would have to use more energy in finding the males which would also open them up to predation whilst on the search for them. This could result in a decrease in the population as less mating would occur.
Costs and Benefits
A benefit to this way of communicating is the female can find the males quicker, assisting with the proximate cause of attracting the attention of the female. Since they can listen to where the sounds are coming from, they can use this to get their location instead of having to look around until the Grouse are seen. However, an issue with this is because of the distance the noises can travel this can attract predators in the area, putting the Greater Sage-Grouse in danger during this time. Similarly, this will give other males an identification on where a lekking site is so they will join. This will increase the competition between the males making it harder for them to attract a female meaning they have to use more energy to get noticed (Nordell et al, 2017). Another cost to this is the overlap from other Sage-Grouse at the same lekking site (Goller et al, 2009). This can cause confusion to the female as to which male is making the loudest noise. Likewise, other noises in the area can distract them from their displays leading to unsuccessful mating (Blackwood et al, 2012). Yet, noise abundance could distract potential predators and leave them confused as to where the lekking site is or for them to mishear and not be able to identify the species that is making the noises (Blickley et al, 2013).
In conclusion, Greater Sage-Grouse use a variety of methods to communicate to different individuals with each one transmitting a different message. This can either be interspecific or intraspecific communication depending on the reason for the message. The ways in which they communicate also has an influence on optimal foraging and sexual selection, affecting how successful they are with this. Not all these methods are beneficial and do have some problems, as information that is transmitted is not always exchanged accurately and this can cause confusion between individuals. However, they have adapted to communicate in the best way possible in order to survive and thrive (Udell et al, 2013: page 259).
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