Problem ER14

The bearded vulture (Gypaetus barbatus, Fig. 5) is a bird of prey that eats mainly carrion and lives and breeds on crags in high mountains. Recently, it has been introduced again in the Alps (in particular in the Stelvio National Park, Italy). Shaub et al. (2009) report data on the numbers of vultures in the Alps between 1996 and 2006 (see table here below) and estimate that the birth rate (number of juveniles produced by a pair of vultures that will survive up to the reproductive age) is 0.6 year$^{-1}$.

Year	1996	1997	1998	1999	2000	2001	2002	2003	2004	2005	2006
Number of pairs	1	1	2	4	4	5	6	6	8	9	9

The reintroduction has been luckily successful because, given an initial population of two birds only in 1996, the vultures have now established in the Alps and the most recent estimate evaluates their population to have reached about one hundred individuals.

However, owing to demographic stochasticity, the reintroduction might have been less successful. Estimate how many vultures (males + females) should have been introduced into the Alps in order to have a long-term probability of success equal to 95%.

Figure 5: The bearded vulture.