Bio Magnification

Nature Games and Activities for Church Camps

Chemicals that humans release into the environment quickly make their way into the bodies of various animals. Many of these chemicals lodge in the fat tissue of the animals and are not excreted from the body. The chemicals have a relatively low concentration in zooplankton and other low-level consumers, but the chemicals quickly accumulate in top predators in the ecosystem. For instance, various raptors suffered the effects of DDT during the 1960's. DDT caused various problems for the birds especially by causing thin egg shells, which lead to a reproductive decline of the species.

Chemicals accumulate in top predators as a result of biomagnification. Put simply, if I eat a chicken, I also eat all of the chemicals that the chicken ate. So if my diet is entirely chickens, I eat seven times as many chemicals in a week than a chicken would have eaten up to that point in their life. Similarly, if an osprey relies on fish as a major part of its diet, than it consumes all of the chemicals stored in the bodies of those fish after they have spent a lifetime building up chemical residue.

Demonstrate biomagnification by spreading a variety of milk jug lids around a grassy area. Pick six participants to serve as predators. The rest of the group represents zooplankton and must gather the milk jug lids as their food. After all of the campers have gathered some lids, send three campers into the field as small fish. Instruct small fish to capture two or three zooplankton, and take their milk caps. Then, send two campers, representing large fish, into the field to catch the small fish. Finally, the last camper represents the osprey and eats both of the large fish, inheriting their store of milk caps.

After the demonstration, enter the situation and look at the hawk's store of lids. Inform the campers that all of the green lids represent DDT, a harmful chemical that causes thin egg shells and thus poor reproduction rates because of diminished chances that newly-laid eggs will survive the mother's weight. Walk through each stage of the food pyramid, asking the campers how many green caps they had at each level. Help the campers to see that gradually, lots of DDT becomes embedded in the hawk from throughout the entire ecosystem. Discuss the problems of DDT and what was done to solve that problem. Also mention the current problem with PCBs and the problem they lead to in killing fish and causing reproductive problems in birds. The chemical's effect is so potent that even a small amount is detectable, such as through nest building irregularities among Tree Swallows. In this game, campers explore the difficulties that birds (and animals overall) face when trying to pass on genes. Explanation is a little bit long for this game, so use it with groups that can concentrate to hear how the game is played.

Set up for the game in a large area with multiple habitats. Lay out nests for the birds in this area, perhaps using old grain sacks or carpet squares. Place some in the open and some in more sheltered areas. Also spread copious amounts of bottle caps of different colors to represent food resources in the game.

Explain that the campers form family groups for this game and try to collect enough food to fledge a baby and return it successfully to home base, all the while avoiding predators. Families consist of one baby, a mom and dad. A baby is safe when on the nest with one parent in contact with the nest. The parents are safe whenever touching the nest. The baby is a sitting duck if alone and can be "eaten" unless another family or parent comes and saves it. Families may move to a different nest if it is open or only has a chick on it.

Parents must bring food back to the nest one peice at a time as birds in the wild can only carry so much in their beak or crop. When all the food is brought back, the baby then is a flighted immature bird and can fly. Whatever family remains must then migrate down to the given site of saftey. Those birds are done and have SURVIVED.

Predators must use associated predator noise and facial expressions and try to tag parents or newly grown birds trying to collect food or "survive." If a bird is tagged, it then becomes a predator and must act like one. A bird is not allowed to become a predator in disguise and trick other birds into being tagged. Predators can't harrass one nest unduly or play unfairly.

Parents, new adults, or groups of roaming birds may mob the predators by holding hands in groups of 3 or more. If a predator is tagged by the mob, the predator must sit down and count slowly out loud to 20. If a predator is tagged a second time by a mob it then becomes a bird again and must go to a nest, either empty, or substituting for another deceased parent.

Allow the game to continue until all of the birds have either become predators or returned successfully to the home base. Discuss the different complexities of the game, including th location of the nests, the availability of food, and the use of mobbing. Ask the campers if it is easy to survive and raise young in the wild. Ask if any families used other nests to survive or adopt other birds. Explain that adoption is rare but not unknown in the wild as birds try to raise young in the nest. In conclusion, mention Christ's words that God provides for all of the little birds (Matthew 6.25), but yet the birds must still go out and collect the food which God has given to them. In the same way God provides for all of our needs but we still work in participation with God.