Assessing migration of Ruby-throated Hummingbirds (Archilochus colubris) at broad spatial and temporal scales
Jason R. Courter, Ron J. Johnson, William C. Bridges, and Kenneth G. Hubbard
The signs of global climate change are ever clearer such that even conservative politicians are grudgingly acknowledging its existence. Not surprisingly, therefore, organisms are responding, and as Courter et al. show, change can be extensive with potential implications for the bird’s biology. Courter et al. utilize resurrected citizen science data from the North American Bird Phenology Program that date back to the late 19th century, and combine them with recent citizen science data, to document advancement of up to 18 days in spring arrival dates of migrant Ruby-throated Hummingbirds in North America. Indications are that migrants delay departure from more southerly locations in North America in warmer winters and springs, and that migration speed has slowed in recent times so that arrival at more northern locations is possibly delayed in relation to local phenology, creating potential mismatches between arrival and availability of early spring food. Finally, the study carries an important message for us all: the ability of these authors to conduct a temporal analysis of arrival date of this extent speaks to the foresight of our predecessors and obligates us to continue for those that will follow us.
Life-history tradeoffs in Spotted Owls (Strix occidentalis): Implications for assessment of territory quality
M. Zachariah Peery and R. J. Gutiérrez
Demographic studies of California Spotted Owls (Strix occidentalis occidentalis) driven by threats of extinction from loss of critical old growth forest habitat, and more recently, invasion of said habitats by congeneric Barred Owls (Strix varia), have set the standard for comprehensive population studies of long-lived vertebrates. The detailed long-term data sets and thorough statistical analyses have provided a sound foundation for the development of management plans that will hopefully prevent the extinction of this deep forest icon. A possibly unintended benefit is that the available data can also be used to test life history theory in ways that are rarely possible. Peery and Gutiérrez took advantage of this opportunity to test for trade-offs between number of offspring fledged and their survival. Interestingly, young fledged as pairs had higher survival as fledglings, subadults, and adults than young fledged as either singletons or triplets. The poor success of singletons possibly reflects either low parental or territory quality, while the reduced success of triplets no doubt represents a classic true intergenerational cost of reproduction. Still, the cost of fledging three young was not great enough to offset the gain in fitness from producing a third fledgling. Although “costs” exist, they do not appear to be great enough to compromise the use of offspring production to help managers evaluate territory/habitat quality for the purposes of planning and managing forests.