Releasing giraffes is an event. Establishing a population is a process, and its early years can be difficult to interpret.
In three Ugandan areas where Nubian giraffes were introduced, the first documented calves arrived roughly three years after the initial releases. A brief follow-up could have ended before reproduction began. A 2025 study led by Michael Butler Brown stayed with the populations long enough to record subsequent growth and, in one park, a second locally born generation.
The work provides evidence that these translocations progressed through the establishment phase. It also shows why the date of release, the first birth and the eventual persistence of a population should be treated as different milestones.
Following the animals after the trucks left
Uganda's translocation programme drew founders from northern Murchison Falls National Park. It established giraffes at Lake Mburo, in Murchison Falls south of the Nile and at Pian Upe, while also reinforcing the existing small population in Kidepo Valley.
The programme was intended to reduce dependence on the large northern Murchison Falls population. A 2019 national assessment had shown that more than 90% of Uganda's estimated adult and subadult giraffes were concentrated there. Distributing giraffes among more sites could spread that risk, but only if the recipients supported animals over time.
Brown and colleagues followed both sides of the transfer. They assembled individual photographic encounter histories for the recipient populations and continued monitoring the donor population.
Coat patterns allowed an animal seen in one year to be recognised in another. Repeated sightings could then establish known births, documented deaths and the probability of detecting a giraffe during a survey. Where the data were sufficient, statistical models adjusted abundance estimates for animals likely to be alive but missed.
The monitoring was not identical everywhere. Some populations had repeated structured surveys; others also relied on opportunistic observations. Southern Murchison Falls was particularly difficult to survey from vehicles. These differences affected which demographic quantities the researchers could estimate reliably.
A delay before the first calves
Lake Mburo received 15 giraffes in 2015: 11 females and four males. Its first documented birth came in May 2018, 35 months after release.
At Pian Upe, releases in 2019 and 2020 established the founder group. The first recorded calf appeared in September 2022, around 34 months after the initial release. Southern Murchison Falls recorded its first calf in April 2019, 39 months after the first introduction.
These intervals are times to the first documented birth, not a guarantee that every earlier birth would have been detected. They nevertheless show a consistent feature of the records: reproduction became evident after a substantial waiting period.
The researchers suggested that founder age helped explain this delay. Animals selected for transfer were mainly subadults or young adults. Females still approaching reproductive maturity would require time before producing calves, even in a suitable environment.
That interpretation is plausible, but the study did not experimentally separate maturation from adjustment to a new site or other influences. A three-year gap cannot by itself be diagnosed as translocation stress. Nor should it be treated as a universal waiting period for every future introduction.
Founder composition changes what an observer should expect. A group containing younger females has a different short-term reproductive timetable from one composed of established breeding adults.
Evidence that establishment continued
The subsequent records supplied more than a first calf.
By March 2024, Lake Mburo's estimated population was about 52 giraffes, with a 95% confidence interval of roughly 39–68. The study recorded 39 reported births since the founders arrived. In February 2023, researchers first documented offspring from the generation born within the park.
That second generation is a consequential milestone. It shows that at least one locally born female survived to reproduce. The population was beginning to replace its founding animals through its own reproductive history.
Pian Upe also grew after births began. Its April 2024 abundance estimate was about 40 giraffes, with a confidence interval of roughly 34–49. Kidepo's reinforced population increased as well.
The histories included deaths. The paper documented mortality among some translocated adults, and Lake Mburo had two known calf deaths. Recognising these losses is part of judging the programme, rather than an exception to reporting its growth.
Southern Murchison Falls illustrates a separate limit. Researchers recorded many giraffe encounters and births, but the available sampling did not support a formal survival estimate. Its catalogue of individuals encountered over several years should not be presented as a precise count of animals alive at one moment.
What high survival estimates leave out
In the recipient sites with sufficient data, the models generally estimated high annual survival. That result supports the establishment assessment, but its observation process needs to remain visible.
A photographic survival model starts with animals that enter the encounter record. A calf born and dying between surveys may never enter that record. At Lake Mburo, the two documented calf deaths occurred outside the regular survey encounters used in the model.
Consequently, a very high modelled survival rate does not establish that almost every calf survived from birth. It describes survival conditional on the animals and occasions represented in the analysed histories.
There is another distinction between sites. The donor population's analysis used survival over seasonal intervals of approximately three months. Recipient estimates were expressed annually. Both may be high, but the numbers cannot be compared as if they covered the same length of time.
These qualifications do not erase the observed births or growth. They identify what the monitoring can establish and where more continuous observation would improve the assessment.
Checking the population that supplied the founders
A translocation can benefit a recipient while imposing a cost on its source. Evaluating only the release site would miss that possibility.
The northern Murchison Falls study recorded repeated encounters from 2014 to 2023 and explicitly accounted for animals removed through translocation. Its final estimated abundance was 1,736 giraffes across all age classes, with a 95% confidence interval of approximately 1,576–1,809. The population continued to increase across the monitoring period.
That finding is reassuring within the programme studied. It does not establish the abundance the donor population would have reached without removals, because the study had no otherwise identical population assigned to a no-removal treatment.
It also does not identify an unlimited sustainable supply of founders. Future removals would need to be evaluated against the donor population's condition, composition and trajectory at the time.
The older national assessment counted adults and subadults in its principal abundance estimate, whereas this later analysis included all age classes. Those headline totals cannot be used alone to calculate an exact percentage recovery between studies.
A longer definition of success
By the period covered in the paper, Uganda had increased the number of its Nubian giraffe populations from two in early 2015 to five in 2024. Monitoring showed reproduction and growth after the initial introductions, with donor population growth continuing alongside the programme.
Those are substantive establishment outcomes. Long-term persistence remains a further question, especially for small populations exposed to changing habitats, demographic chance and future threats. The study did not measure every component of genetic or ecological viability.
Its practical contribution is the timetable and the evidence behind it. Release numbers describe a management action. Survival records show whether founders remain. Births reveal reproduction, and locally born animals reproducing themselves show another stage of replacement.
In Uganda, the first conspicuous sign of that replacement took years to appear. The monitoring programme lasted long enough to recognise it.
Sources
Michael Butler Brown, Herbert Kasozi, Robert Aruho, Stephanie Fennessy, Sara Ferguson, Arthur Muneza and Julian Fennessy (2025). Assessing the success of conservation translocation establishment: Post-translocation demography of Nubian giraffe (Giraffa camelopardalis camelopardalis) in Uganda. Conservation Science and Practice, 7, e70127.
Michael B. Brown, Douglas T. Bolger and Julian Fennessy (2019). All the eggs in one basket: A countrywide assessment of current and historical giraffe population distribution in Uganda. Global Ecology and Conservation, 19, e00612.
