| Demographic Modeling of Migratory Bird
Populations: The Importance of Parameter Estimation Using Marked Individuals Thomas W. Sherry1and Richard T.
Holmes2
| ABSTRACT— We argue that
monitoring of population abundance, or even of general demographic features such as
nesting success, is not sufficient to understand what factors cause migratory bird
population declines or changes in abundance. Instead, a demographic approach is needed,
based on data from marked individuals and coupled with population modeling. The dynamics
of a population can be modeled most simply using only one parameter, the population growth
rate, which is given by the per capita birth rate minus the per capita death rate. Simple
model refinements, including habitat- and season-specific vital rates, can add
considerable realism and model utility. Empirical estimation of vital parameters requires
monitoring the activities and fates of uniquely marked individuals. With such models and
parameter estimates one can (1) assess whether particular populations have sufficient
production of offspring (e.g., by habitat) to offset annual mortality; (2) investigate
ecological influences on population dynamics, including effects of winter versus summer
circumstances, population size, and actual or hypothetical environmental changes; and (3)
identify where new empirical data are most critical (e.g., dispersal, age effects.We
illustrate these points with emphasis on long-term data on color-banded Black-throated
Blue Warblers (Dendroica caerulescens) and American Redstarts (Setophaga
ruticilla) in the Hubbard Brook Experimental Forest, NH, and in Jamaica, and we
discuss practical aspects of parameter estimation and demographic modeling for migratory
species. |
1Department of Ecology
Evolution and Organismal Biology
Tulane University
New Orleans, LA 70118
2Department of Biological Sciences
Dartmouth College
Hanover, NH 03755 |