Wild reindeer calf recruitment variations; biology or methodology?
The two field methods, ground counts and aerial photography, currently used for calculating population estimates and calf recruitment for Norwegian wild reindeer (Rangifer tarandus) produce different results. Using population count data by both methods from the same years in various areas, I systema...
| Published in: | Rangifer |
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| Main Author: | |
| Format: | Article in Journal/Newspaper |
| Language: | English |
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Septentrio Academic Publishing
2009
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| Subjects: | |
| Online Access: | https://doi.org/10.7557/2.26.1.183 https://doaj.org/article/71886510d94a4f109013d8da84ab39c0 |
| Summary: | The two field methods, ground counts and aerial photography, currently used for calculating population estimates and calf recruitment for Norwegian wild reindeer (Rangifer tarandus) produce different results. Using population count data by both methods from the same years in various areas, I systematically compare estimates of sex and age components and decipher reasons for the discrepancies found in previous estimates made by each method. Data for aerial photography counts were found in the literature, while original data is presented for ground counts. Calf recruitment (calves/100 females) and the proportion of adult males (males 1+ years/100 animals 1+ years) in herds of reindeer in Norefjell-Reinsjøfjell (1993-98), Rondane North (1995-97) and Setesdal-Ryfylke (1995, 1998) were recorded from ground counts of post calving groups in June-July. The estimates for number of calves per 100 females 1+ years were lower and more variable than number of calves per 100 females 2+ years. A variable number of yearling females in the groups and difficulties in correctly sexing yearlings are contributing factors. The estimates for number of calves/100 females 1+ years were higher than calves/100 animals 1+ years due to the inclusion of young males in the latter. Among animals 1+ years in the post-calving groups, males (mostly yearling males) composed from 4.7 to 27.9 %. Nevertheless, both calculation methods for calf recruitment were consistently higher for ground count data than when using counts from air photographs, confirming that the two methods do not produce comparable results. Explanations for this discrepancy are (1) that calves may be easier to overlook on air photographs than in ground composition counts and (2) that the yearling male components in the post calving groups are unaccounted for when using air photographs. June recruitment rates (calves/100 females 1+ years) in Rondane North were also estimated from composition counts recorded from ground counts in October and from air photographs of post calving ... |
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