Background Information:

Most predatory birds live and hunt alone. Harris' hawks are unusual because they live and hunt in groups. In Arizona, nesting groups generally consist of two to seven adult hawks. Biologists are interested in why Harris' hawks form groups when other large predatory birds do not. Do nests represent a shared / community parentage or is only one pair of adults reproducing? What advantage does nesting together provide for an individual bird? Is grouping a result of environmental factors (not enough suitable habitat)? behavioral factors (group activities contribute to individual fitness)? or genetic factors (kin selection/indirect fitness)?

Most of what is known about Harris' hawks results from behavioral studies during which biologists spent hours watching several nests and their inhabitants. Each nesting group has a social hierarchy; individual birds have defined roles. Two dominant hawks (one male and one female), called "Alpha birds", are present in each group. Alpha birds have the greatest access to the nest. They gather building materials, construct the nest, incubate the eggs and care for the young. Additionally they participate in group hunting, the delivery of prey and scaring off predators. Beta birds are also adult birds,but are subordinate to the alpha birds. Beta birds provide a large amount of prey to the nest and contribute to the breeding effort by supplying food for the fledglings. Rarely are Beta birds allowed within 50 meters of the nest. Gamma birds are juveniles. They are subordinate to all other birds. They participate in group hunting and in predator detection, but rarely are they allowed within 150 meters of the nest. Within any level (alpha, beta or gamma), the females are dominant to males.

Behavioral observations by themselves are not enough to explain grouping behavior among Harris' hawks. Parentage cannot be determined solely by observation because defined social roles limit access to the nests by most group members. Furthermore, matings occur away from the nest and are often not witnessed by field biologists. Insights into the nesting behavior of the Harris' hawk must be sought through other fields of biology. The application of DNA profiling and molecular biology techniques can provide insights into the parentage and genetic relatedness of the group members.

Form A Hypothesis

1. What do biologists' hope to learn about Harris' hawks by determining who the parents of the baby birds are?

2. Based upon their behavioral roles, which birds do you believe are reproducing in each nesting group? Why?

Genetic Information about Nesting Groups

Biologists trapped and collected blood samples from all of the birds at each nest. This did not harm the Harris' hawks. They extracted DNA from the blood cells and created a DNA profile for each bird. By comparing the DNA profiles of the juvenile birds with all of the adult birds' DNA profiles, they determined which birds were reproducing at each nest.

You will be given DNA profiles and behavioral data from several nests to analyze. Click on the name of the nest to access its behavioral and genetic data. For each nest, you will need to determine the behavioral roles of the hawks, which birds you believe are reproducing (based upon behavioral data), the parents of all nestlings, and which birds are actually reproducing. You will also need to turn in copies of the DNA profiles you analyze with the informative bands colored to match the source parent. Record your data in the table below:

(SEE How to Interpret DNA Profiles)

Nest	Parents	Number of Adults at Nest	Number of Adults Reproducing	Does the genetic data support the behavioral data?
Double Arrow	n1 - n2 -	______________	_____________	______________
Pancho Villa	n1- n2 - n3 -	______________	______________	______________
Ranch 1988	n1- n2 - n3 - n4 -	______________	______________	______________
Ranch 1989	n1- n2 - n3 -	______________	______________	______________
Milepost 246	n1- n2 -	______________	______________	______________

DNA Profiles and Mendelian Genetics

Study the DNA profile obtained at the Double Arrow Nest. Answer questions #3-8.

3. How many bands does n1 have?

4. How many of these bands could have only been inherited from the mother?

5. How many of these bands could have only been inherited from the father?

6. Are there any bands which are shared by both parents?

7. Are there any bands which are present in the offspring which are not present in the parents?

8. Think of each band as a phenotype, explain why unrelated individuals may share some bands.

Using All of the Data to Revise a Hypothesis.

9. Overall, does the genetic evidence support the behavioral evidence? Explain your answer.

10. When biologists' form hypotheses about why Harris' hawks nest together, they must consider both the advantages and disadvantages of group living. Make a list of three animals you know which live in groups. List some of the advantages and disadvantages they face because they live in a group.

Animal	Advantages	Disadvantages
1.	a) b)	a) b)
2.	a) b)	a) b)
3.	a) b)	a) b)

Group living is not common within the animal kingdom. When animals live in groups, they do so for many reasons.

• Habitat saturation - The area that they live in has limited resources and suitable habitat. Individuals may leave and try to establish territories in less desirable areas or they may join a group as a subordinate. By joining an established group, there is the possibility of mating opportunities, inheriting the territory, or surviving until a suitable territory can be obtained.SEE Hunting Success and Group Size Chart
• Kin selection - Our relatives share some of our genes. Helping a sibling reproduce and raise their young is almost like reproducing yourself.
• Living with Parents until Older - Juveniles may stay with the group while they gain life skills necessary for survival on their own. Eventually, when they are older and more likely to survive on their own, they will leave the nest and establish their own territory. SEE Status of Hawks Which Left Their Natal Nest and Joined Unrelated Groups

11. Based upon your knowledge about the behavior and genetic structure of Harris' hawk groups, why do you think s Harris' hawks from the Southwest United States live in groups while Harris' hawks from South and Central America do not?

12. Does your conclusion support your initial hypothesis?

13. Why is it important to use many types of data (ex. molecular, behavioral, etc.) when forming a hypothesis?

Science Education Connection Department of Biochemistry The University of Arizona Tuesday, January 14, 1997 warder@u.arizona.edu http://biology.arizona.edu/sciconn/lessons/vuturo/ All contents copyright © 1997. All rights reserved.