Modeling Captive Rearing

photo of a piping plover with a chickAbstract

Doolittle, A. 2000. Modeling Captive Rearing. Ph.D. Dissertation, Univ. of Minnesota, Minneapolis.

The endangered Great Lakes Piping Plover population remains small, with < 35 pairs since federal listing in 1986. Captive rearing and reintroduction currently are conducted opportunistically on a small scale (0-9 fledglings released per year) using eggs abandoned in the breeding range. To examine potential usefulness of proactive captive-rearing and reintroduction strategies in recovery of the population, I developed a computer program to stochastically model the population over time using data collected from the actual population. I tested the effects of five different strategies on the model population and examined population change over 20 model-years. The control strategy (no model eggs removed) simulates current management of the actual population. In two captive-rearing strategies, the program simulated removal of entire clutches from 10% or 25% of nests; I assumed renesting by pairs from which clutches were removed. In the other two captive-rearing strategies, single eggs were removed from 50% or 100% of nests; I assumed model pairs continued to incubate remaining eggs and did not lay replacement eggs.

Captive rearing significantly increased population levels under my initial set of assumptions. The effectiveness of captive-rearing strategies was reduced when the survival of captive-reared fledglings was lowered by 50%; strategies were detrimental to the population when survival of captive-reared birds was zero. Although captive-reared birds have been recruited into the Great Lakes and Great Plains Piping Plover populations, more information is needed about their rate of return to better assess the effectiveness of captive-rearing strategies.

I used a variety of criteria to assess the relative benefits and risks of different captive-rearing strategies, including mean population size after 20 years and probability that the population would double or decline in 20 years. For most criteria, the performance of each strategy relative to the other strategies varied considerably when assumptions were changed. For one criterion, population increase per egg taken into captivity, the performance of each strategy relative to the others remained fairly consistent under the range of assumptions tested. Population increase per egg may also be a useful means of assessing the cost-effectiveness of captive-rearing strategies. In general, double-clutching strategies outperformed single-egg removal strategies in population augmentation, but behavioral and genetic consequences of double clutching need to be considered before it is adopted as a management strategy.