Demography and Populations

Based on estimates of 2.9 breeding pairs/ha in their study plot, 1-2 floaters per breeding pair, and an estimate of 790 ha of suitable breeding habitat, Oliveras de Ita and Gómez de Silva (2007) estimated a total population size of 5,380-6,150 adults (2,300 breeding pairs) for Sierra Madre Sparrow. Other studies estimate population sizes of at least 10,000 individuals, roughly equating to 6,700 mature individuals (Wege and Long 1995).

Sierra Madre Sparrow nest success at La Cima was relatively low although similar to that of other grassland sparrow species. Of nests monitored (n = 14), five (36%) were successful. Six failed due to chick predation and one due to egg predation; 2 failed due to death of or abandonment by the female. No predation events were directly observed but multiple potential mammal, reptile and avian predators were observed (Oliveras de Ita et al. 2001). In contrast, based on the return rate of territorial males, adult survival was higher than that reported for other migratory sparrow species (Oliveras de Ita and Gómez de Silva 2007).

Autopsies conducted on two Sierra Madre Sparrows that died in the hand while mist-netting revealed high degrees of mycotoxicosis and damage to heart, liver and other organs. This suggested that the sparrows had fed on contaminated grain (Oliveras de Ita et al. 2001).