Avian Projects

Owl Irruption Patterns

Several species of northern owls are known to irrupt in winter far south of their normal winter ranges.  These include Snowy Owl (Bubo scandiacus), Great Gray Owl (Strix nebulosa), and Northern Hawk-Owl (Surnia ulula).  This research is focused on describing the patterns of irruptions and how they might have changed in recent decades, then evaluating whether climate change might be responsible, at least partially, for those changes.  Sources of data are Christmas Bird Counts and seasonal reports in Audubon Field Notes (and all its various name changes through the years).

Preliminary results for the Snowy Owl were presented at the 2020 North American Ornithological Congress:

Coldren, C. L. Snowy Owl irruption patterns and the potential impact of climate change. North American Ornithological Congress, 11 August 2020, San Juan, Puerto Rico, given virtually.

Historical Changes in Avian Demography

Human development in North America has brought a multitude of changes in the landscape, and with it a variety of threats to avian populations across the continent.  Changes in land use, habitat fragmentation, and urbanization are among the landscape-level alterations that birds must cope with for survival.  Additionally, widespread changes in automobile use and chemical contaminants may impact bird populations as well.  Some basic ecological processes, such as predation, competition, and resource availability, may have been altered as a result of these changes.  If so, these impacts should be reflected in basic demographic parameters, such as clutch size, hatching success, fledging success, survivorship, age and sex structure of populations, territory size, and dispersal.  This research attempts to document changes in these patterns over the course of the last 100+ years.  The primary source of data for the first portion of this period is the early peer-reviewed literature.  In the latter part, some citizen science efforts, such as Project NestWatch, Christmas Bird Counts, and Breeding Bird Surveys, are providing valuable data.

This research effort has been ongoing for a number of years, primarily due to the vastness of the early literature, as well as the lack of search tools we have come to rely on heavily in recent years.  Keywords were unheard of a hundred years ago, and papers often did not restrict themselves to the topic hinted at in the title.  A paper ostensibly addressing reproductive success of one species may contain data on a dozen more species…

My current focus is on a handful of species often found nesting in proximity to humans, primarily Northern Mockingbirds (Mimus polyglottos) and Northern Cardinals (Cardinalis cardinalis), but others as well, including Barn Swallows (Hirundo rustica), Brown Thrashers (Toxostoma rufum), and American Robins (Turdus migratorius). 

Urban Birds

With the increasing impacts of human development on the natural world, urban wildlife communities are becoming more important, for a variety of reasons.  As such, our understanding of the ecological processes acting on urban species is critical to our knowledge of these communities.  Lubbock, Texas, finds itself in a unique situation to address some of these questions.  To the south and the west lie extensive cotton fields, and any trees found in the south and west parts of town are not native, and can be used as a gauge to the age of development.  The avian community in town is somewhat simple, with 8 species dominating, but that mix is unique.  One of the most common species is the invasive and introduced Eurasian Collared-Dove (Streptopelia decaocto).  White-winged Doves (Zenaida asiatica) are also common, and while this species is native to Texas, it's occurrence in Lubbock is fairly recent due to a major range expansion.  In parts of town, another introduced columbiform, the Rock Pigeon (Columba livia), can be common.  And of course, the House Sparrow (Passer domesticus), another introduced species, is ubiquitous.  Other major species are Mourning Dove (Zenaida macroura), Blue Jay (Cyanocitta cristata), Northern Mockingbird (Mimus polyglottos), and Great-tailed Grackle (Quiscalus mexicanus).  My research is focused on the interactions of this narrow suite of species (some native, some introduced, and some out of their historic range).  Issues being considered are distribution relative to habitat age and development, resource use (primarily food and water), and social interactions.