Duck Breeding Success Factors

Lesser Scaup 4 713

Biologists study various factors that might influence ducks (Lesser Scaup) on the refuge to be more or less successful at breeding. Factors such as age, previous year breeding success, body health, environmental conditions and random influences are examined.


 Short Title: Duck Breeding Success Factors

 

 Longer Title: Factors important in decision to breed in Lesser Scaup.

 

 Original Title: Previous success and current body condition determine breeding propensity in Lesser Scaup: evidence for the individual heterogeneity hypothesis.

 

Authors: Jeffrey M. Warren, Kyle A. Cutting. John Y. Takekawa, Susan E. De La Cruz,Tony D. Williams, and David N. Koons

 

Short Description of Science Project:

 

It is important to understand the factors that are important in breeding success for ducks. This study looks at the factors of age, previous success at the same location, and body condition to understand which factors are more important for breeding success for the Lesser Scaup, a small diving duck found at the refuge during spring and summer.

 

 Where was it done?

 

The study was done on the Lower Red Rock Lake at the refuge (at 6600 feet). This wetlands area consists of a  shallow lake (5 feet) interspersed with hardstem bulrush islands. Much of the area consists of extensive stands of seasonally flooded Northwest Territory sedge that contain small areas of open water. This is a harsh breeding area due to the variable environments year to year and cold weather at the beginning of the breeding season.

 

How was it done?

 

Female Lesser Scaup (213) were captured at night from boats using spotlights. These birds were leg-banded and age estimated on the basis of eye-color. Each bird was weighed, and measured. The oviduct of the female was palpated to see if an egg was present. If not, blood was extracted for later analysis of blood proteins to indicate if breeding had occurred. A feather sample was cut from the first primary feather for later analysis of breeding location.

 

Blood collected was analyzed to determine zinc levels which are predictors of breeding activity due to depletion of a lipoprotein used in egg production.

 

Feathers collected were analyzed using carbon and nitrogen isotope analysis to determine if the ducks had bred in the refuge the previous breeding season. Feathers collected in the previous year were used as controls to compare.

 

In population biology, various software models and statistical procedures have been developed to help analyze the data and make meaningful predictions. This project used several such models to investigate trends in the data collected.

 

Results of the Science Project.

 

The study determined that of the 213 captured females, 57% had bred that season. Of the feather analysis, there were 145 females sampled and only 32 of them (22%) were determined to be present on the refuge in the year prior to capture.  There was a strong relationship between duck health and breeding success. Those ducks with good body condition were more likely to breed in the study year than those with a lesser health status.

 

The study did not find an expected correlation between age and breeding success. The study expected to find that older ducks were more successful in breeding than younger ones based on prior studies in other species.

 

The study also found that previous success in breeding at the refuge predicted a favorable breeding probability for the future.

 

Drought was a negative factor in breeding success, but the study's prediction that it would affect younger ducks more than older was not substantiated.

 

It is difficult to understand from this study the cause and effect of drought. Did drought cause the ducks to refrain from breeding because they had an understanding of the outcome in such conditions or did the drought affect the environmental conditions (such as water levels and lesser food sources) such that ducks could not be as successful in breeding?  

 

This study concludes by stating that individual heterogeneity or variations from one duck to the other caused by many factors probably affected the breeding success more than anything. 

 

Link to the Original Paper: PDF