Male-mating strategies in elephant bulls


Save the Elephants

Date Published

His work combines behavioral observations together with faecal sample collection for hormone and DNA analyses, and detailed monitoring of elephant movements using Global Positioning System collars and radio tracking. The radio-tracking work is part of a larger study by Dr. Iain Douglas-Hamilton examining the movements, hotspots and corridors of elephants throughout the Samburu/Laikipia ecosystem.

Henrik’s work is currently funded by Save the Elephants, The International Elephant Foundation and the Dawkins Prize for Animal Conservation and Welfare (awarded to Iain Douglas-Hamilton in 2001). Summary of behavioral observations and movements of collared Samburu bulls June 2002Henrik Barner RasmussenPh.D. Researcher, Save the ElephantsEsidai B1027: Collared with GPS1000 collar, beginning of February 2002. Unfortunately, the collar malfunctioned and went into emergency after 2 days.

The 37 year old bull Esidai is a medium ranking bull in the Samburu population and has been followed closely for the last 2 years. He has previously been collared and an almost complete record exists on his movements for the whole of year 2000 as well as more than 50 hours of detailed observations on his behavior.Two main areas are used by the bulls when they are not sexually active and searching for receptive females. One area to the west of Save the Elephants camp and one area approximately 50 km east of our camp. The two areas are used by two different groupings of bulls. Esidai is a typical “Western bull” spending most of his time together with other bulls along the Ewaso Ngiro River between 10 and 40 km west of our camp.

However, twice a year, during the two rainy seasons, he leaves his friends in order to search for estrus females. During these periods he sometimes come in musth, hereby signaling his focus on reproduction and warning other bulls of his aggressive state of mind.He was collared in the beginning of February less than 500 meters away from our research camp in Samburu. Already the following day he was calmly browsing from the trees next to our tents indicating no hard feelings towards the two-legged creatures who had given him an 8000$ necklace the previous day!

The following two months he mainly stayed alone or together with some of the other western bulls like Abe, Mungu, Kenyatta, Matt and Picasso. During April he slowly started to drift in towards the central part of the reserve and soon he was seen cruising around searching for receptive females. During the two months he spent searching for receptive females he was only seen in musth the last 2 weeks before he left back east to meet up with his bull friends. He was seen following estrus females several times and was also seen successfully mating a young female from the family group “Biblical books” although he on most occasions had to accept the role as second or third ranking bull.

The lack of musth signaling was probably due to the presence of three other large musth bulls in the area, forcing him to keep a low profile. However, he had a constant standoff going on with another medium ranking bull, Apollo (also collared, see below) from the eastern group of bulls and after this season, it was pretty clear that they would probably never be close friends.Since he was collared, we have collected faecal samples from him every 10th day as we do with all our collared bulls.

This will, in a years time, for the first time ever reveal a complete hormone profile on androgens and cortisol (stress hormones) in free ranging elephants and will, combined with our GPS tracking and behavioral observations, give us the most complete picture of a year in the life of a fully grown bull elephant to date. Apollo B1033:Collared with a GPS1000 collar at the beginning of February 2002. With his approximately 38 years, Apollo is only slightly older than Esidai. He is coming from the grouping of bulls we call “eastern bulls” and is normally not associating with any bulls from the western area unless competing over estrus females.

His close match with Esidai in age and rank combined with a different home area was the main reason to collar Apollo in order to see how and if these two bulls interacted. After a short one-month period of musth, during March, mainly spent south and east of Shaba National Reserve, Apollo shifted into Samburu and Buffalo Springs National Reserve during April, May and June. Here he not only found high numbers of females, many coming into estrus due to the above average rainfall this season, but also three to four large bulls in musth, namely Mungu, Abe and Kenyatta (see below) and the now infamous, highly aggressive Rommel who during a fight with Abe attacked and annihilated one of our research cars. Faced with this level of competition Apollo apparently decided to drop out of musth but continued to search for females.

During this period Apollo had an almost continuous conflict with Esidai over the right to be the highest ranking, non-musth bull in the area. In May, Apollo was clearly number one of the two and chased Esidai away on several occasions. However, During June Esidai began to stand up to Apollo and in mid June it came to a full contact struggle when they met and fought over Matisse a female from the family unit ‘Artists’. Again Esidai had to back out but only 5 days later they met again, this time Esidai had started on his short 2 week period of musth and apparently Apollo knew that Esidai was now serious.

After a four hour standoff, including parallel walks and the destruction of several trees, both bulls decided not to engage in full scale fighting and they went in different directions with no clear winner. It will be interesting to see how this conflict develops in the future. In two years time, when the calves conceived during this season are born we will make paternity analysis and then see which of the bulls has fathered the calves. This, combined with the knowledge on the different strategies and ranks among the bulls, will give us information of the payoff from the different reproductive strategies.Mungu B1001: Collared with a GPS2000 collar in mid March 2002.

Mungu, meaning “God” in Kiswahili, is one of the largest of the western bulls and has without doubt the largest tusks in the whole area. Shortly after he was collared in March he came into musth and shifted range into the core area of the reserve. Here he spent the last 2-3 months within a relatively small area overlapping with the area used by most females. During this period he has been observed for many hours in order to get information on bull behavior both during musth and during periods of non-musth. Mungu dropped out of musth by the end June and immediately made a large trip west. Within three days he covered more than 80 km, in a straight line ending up around Tale hill.

The following day he decided to return and did most of the journey back within one night.Lewis B1013:Collared with a GPS2000 collar at the beginning of February 2002. Lewis is one of our largest bulls and around 43 years old. He is seldom seen in the area around our camp except when in musth, normally between January to March. He is seldom associating with any of the other known bulls. After he was collared in February (this year he did not come into musth during his normal period) he completely vanished for almost 3 months. After hundreds of kilometers of driving and hours of scanning from the airplane we almost gave up on him and believed the collar had failed since we had covered all the areas our elephants normally frequent.

However, suddenly one day in April we picked up his signal and found him just south of the reserve. Where he had been during the previous 3 months we still don’t know, but as soon as we recover his collar in January next year thousands of GPS positions taken every hour during his absence will hopefully reveal his secret hiding place and most likely surprise us in terms of a new area currently not known to be used by the Samburu elephants. After his re-emergence he has spent all his time south of the reserve mainly alone and not taking part in the competition for females.

It will be interesting to see how he is related to the other groupings of males, this we will know when we get the results from the DNA analysis of bull relatedness by the end of this year. Telonics collarsApart from the four GPS collared bulls, five bulls are currently collared with standard radio collars. Although these collars do not provide the same detailed hourly positions as the GPS collars, they can be used for locating the individual bulls on a regular basis, essential for some of the ongoing research on bull mating strategies and social organization. The advantage of the Telonics collars is that they have an 8 year lifespan and relatively low cost compared to GPS-collars.Ansel B1039:Collared with a Telonics radio collar in mid March 2002.

After 2 years of detailed recordings with GPS collars, Ansel, an approximately 28 year old bull, had his collar replaced in March 2002 with a traditional radio collar. GPS collars can at present only record positions for one year before the battery needs replacement. Therefore continued monitoring of individuals requires immobilizing them once a year. At Save the Elephants we have developed a minimum impact procedure for collaring. However, from a precautionary principle we do not want to continue immobilizing the same individual more than a few times. Since Ansel has shown interesting behavior over the last 2 years we wanted to continue to track him and therefore replaced the GPS collar with a radio collar capable of transmitting for more than 8 years.

Ansel has to date not been seen in musth but has prolonged periods of sexually active non-musth. Very little attention has presently been placed on the behavior of these low to medium ranking bulls. However, results from Henrik’s Masters thesis, carried out between 2000 and 2001 indicated clearly that alternating periods of sexual activity and inactivity were combined with large investments in searches for receptive females among this group of bulls. Therefore more focus has and will be placed on these younger bulls during the next two years. Since Ansel was re-collared in March he has mainly been seen within the reserve boundaries often associating with females.

However, previously he has made large trips both east and west, covering an area more than 130 x 80 km. He has probably not settled down within any of the bull groupings yet and spends time with both the eastern and western bulls.Picasso B1041: Collared with Telonics radio collar at the beginning of June 2002. With his 30 years of age, Picasso is in a transition period between playing a clear subordinate role to becoming a bull occasionally able to dominate his competitors. Picasso has occasional, short periods of musth although mainly occurring in less attractive periods of the year. Detailed GPS recordings could be interesting, however he was collared with a telonics radio collar due to financial constraints.

In the period from April to May, immediately before he was collared he was seen in the central part of Samburu National Reserve. Here he was clearly subordinate to all the musth bulls as well as the larger non-musth bulls such as Apollo and Esidai. However, he was still observed mating. On one occasion he was seen mating an estrus female at her peak while the musth bull guarding her was locked in a major conflict with another musth bull. Approximately one month after he was collared he returned to the western bull area and has for the last 4 weeks not been seen outside a small 300 x 300 meter area. Abe B1005: Collared with Telonics radio collar in mid March 2002.

Estimated at 38 years, he is younger than Mungu, However, during this season he has been higher ranking than Mungu, possible due to his higher level of aggression.He has been one of the three “resident” musth bulls for the last 3 months and has guarded and mated several females during that period. Despite musth bulls being more aggressive than other bulls, relatively little conflict has taken place between the three larger musth bulls (Mungu, Abe and Kenyatta). This is probably due to the three bulls all coming from the western area, having a close knowledge of each other’s strength and therefore choosing not to engage in a conflict with a stronger bull.

By comparison, a new unknown bull Rommel who came into the reserve in May was seen fighting with both Abe (to whom he lost) and Mungu (who he chased away) within a period of 5 days although he is both younger and smaller than these two resident bulls. One of the underlying factors behind bull-bull associations is probably assessment of the strength of would-be competitors in order to avoid potentially lethal conflicts when competing for females.

Pretibambam B1009 and Matt B1158: Collared with Telonics radio collars at the beginning of June 2002. Pretibambam and Matt are often seen in the same grouping of bulls in the western area. Both bulls were collared for the first time in June and relatively little is known about them when they are away from our core study area. We know Pretibambam comes into musth every year, around December-February, and spends most of his time in the west. However, detailed recordings over the next two years will hopefully show the social network and ranging patterns of these two bulls.