Population census of Thornicroft's giraffeGiraffa camelopardalis thornicroftiin Zambia, 1973−2003: conservation reassessment required

A drying river let young giraffes cross where only big males had managed. In Zambia's Luangwa Valley, falling water levels changed which giraffes could move between riverbanks. That movement matters when interpreting a local count: more giraffes in one place can mean arrivals, not extra births.

Philip Berry and Fred Bercovitch examined observations collected on foot and by vehicle from 1973 to 2003, with a further survey in 2013. They recognised many Thornicroft's giraffes individually and corrected counts of unfamiliar animals for repeated sightings. To compare years, they concentrated on the western bank and calculated the number encountered per kilometre travelled, rather than treating uneven search effort as a population change.

The long series suggested broadly stable abundance, including a 2013 encounter rate similar to that recorded four decades earlier. An increase around 1994–1995 coincided with low river levels allowing giraffes of different ages and sexes to cross from the eastern bank; previously, crossings had largely involved mature males. The authors estimated about 500–600 giraffes across their range, but this extrapolation was not a complete census. Stability did not remove the vulnerability of a small, isolated population. The study shows why counting animals and understanding their movements belong together.