Rodent control and food supplementation increase productivity of endangered San Clemente loggerhead shrikes (Lanius ludovicianus mearnsi)

Published source details Heath S.R., Kershner E.L., Cooper D.M., Lynn S., Turner J.M., Warnock N., Farabaugh S., Brock K. & Gracelon D.K. (2008) Rodent control and food supplementation increase productivity of endangered San Clemente loggerhead shrikes (Lanius ludovicianus mearnsi). Biological Conservation, 141, 2506-2515.
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This study is summarised as evidence for the following.

	Action	Category
	Release captive-bred individuals into the wild to restore or augment wild populations of songbirds Action Link
	Control mammalian predators on islands for songbirds Action Link
	Provide supplementary food for songbirds to increase reproductive success Action Link

Release captive-bred individuals into the wild to restore or augment wild populations of songbirds

A controlled, replicated study on San Clemente Island, California, USA, between 2000 and 2006 (Heath et al. 2008) found that pairs of San Clemente loggerhead shrikes Lanius ludovicianus mearnsi with captive-bred females produced fewer fledglings and reared fewer chicks to independence than pairs with wild-bred females (2.6 fledglings/pair and 1.9 independent young/pair for 65 breeding attempts with captive-bred females vs. 3.5 fledglings/pair and 2.6 independent young/pair for 107 attempts with wild-bred females). The same pattern was seen with the origin of the male in a pair, but this was not a significant effect (2.6 fledglings/pair and 1.9 independent young/pair for 54 breeding attempts with captive-bred males vs. 3.6 fledglings/pair and 2.6 independent young/pair for 118 attempts with wild-bred females). Other interventions used are discussed in ‘Control predators on islands’ and ‘Provide supplementary food to increase reproductive success’.
Control mammalian predators on islands for songbirds

A controlled, replicated study on San Clemente Island, California, USA, between 2000 and 2006 (Heath et al. 2008) found that 172 pairs of San Clemente loggerhead shrikes Lanius ludovicianus mearnsi produced 1.1 more fledglings when rodents were controlled in their territories during April-July, compared to control pairs. In drier-than-average years, experimental pairs also raised 1.1 extra fledglings to independence (40 days old). However, there was no effect of rodent control on fledgling success in wetter-than-average years. Management in December-March did not increase either measure of productivity. Rodents were controlled with cholecalciferol rodenticide. This study also investigated the impact of supplementary feeding in addition to rodent control, which is discussed in ‘Provide supplementary food to increase reproductive success’ and the success of captive-bred individuals, in ‘Release captive-bred individuals’.
Provide supplementary food for songbirds to increase reproductive success

A controlled, replicated study on San Clemente Island, California, USA, between 2000 and 2006 (Heath et al. 2008) found that pairs of San Clemente loggerhead shrikes Lanius ludovicianus mearnsi in territories provided with supplementary food and with rodent control during April-July produced, on average, 2.5 more fledglings each year (55 breeding attempts), compared to control pairs (62 attempts), and 1.4 more fledglings each year compared to territories with rodent control but no feeding (55 attempts). In drier-than-average years, fed pairs also raised more fledglings to independence (40 days old) than other pairs (1.8 more fledglings than control pairs, 0.7 more than rodent control only pairs). There was no effect in wetter-than-average years. Management in December-March did not increase either measure of productivity. This study also investigated the impact of just rodent control, which is discussed in ‘Control predators on islands’ and the success of captive-bred individuals, in ‘Release captive-bred individuals’.