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Six Cold Days at the Swallow Bridge

Grade 8 natural selection practice: use a wildlife refuge's cliff swallow banding and foster-nest data to explain why some birds survived a cold snap and reproduced.

Grade 8ScienceInteractive · Printable

Aligned toMS-LS4-4

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What’s included

Single worksheet
Auto-graded online
1 NGSS standard
Printable answer key
10 questions
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Details

Format: Interactive · Printable
Grade: Grade 8
Subject: Science
Question types: Fill in the blank, Multiple choice, Circle the answer, Short answer

About this worksheet

What students practice

Students use survival data to explain how a variation in body size affected which birds survived.
Students use foster-nest data to show that body size is inherited and passed to offspring.

How to use

Read paragraphs 1 to 3 together and make sure students know what banding is, then let them work through the histogram and tables before the written explanation.

Curriculum

NGSS standard covered

MS-LS4-4

Explain how genetic variation in traits makes some individuals more likely to survive and reproduce.

Preview

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Name Date

Six Cold Days at the Swallow Bridge

Use a refuge's banding data to explain how inherited body size affected which swallows survived and reproduced.

Part 1: Who survived the cold snap?

Read the passage, the histogram and Table 1, then answer questions 1 to 5.

Banding Day at Sandhill Bridge

1Sandhill Bridge carries a gravel road over a river inside a national wildlife refuge on the Great Plains. Every spring, hundreds of cliff swallows return to build mud nests under the bridge. Desmond Achterberg, an eighth grader who lives near the refuge, helps refuge biologist Noor Halvorsen with the spring animal surveys. In early May they catch adult swallows in soft mist nets, weigh each bird and put a tiny numbered band on its leg before letting it go. Like people, swallows in one colony vary in body size, even when they eat the same food.

2One year, three weeks after banding, a cold, rainy spell settled over the refuge for six days. Cliff swallows feed almost entirely on insects they catch in the air, and in cold rain few insects fly. With little to eat, a swallow must burn the fat stored in its body to stay warm. A larger bird usually carries more stored fat, and it loses heat more slowly for its size than a smaller bird. Many swallows in the colony died.

3When the weather warmed, Desmond and Ms. Halvorsen checked the colony for banded birds that were still alive. Over the next week they read the leg bands with binoculars and a long camera lens as the birds sat at their nests. They grouped the birds by the mass each one had in early May, before the cold spell (Table 1). They found no banded birds that had joined other colonies, so they treated a missing bird as one that had died.

4Ms. Halvorsen also had data from an earlier study at the bridge. Biologists had swapped some eggs between nests, so that chicks were raised by foster parents. When those chicks grew up, the team weighed them as adults and compared them with both their genetic parents, who laid the eggs, and their foster parents, who fed them (Table 2). Swapping eggs is a common way to sort out which traits come from the parents' genes and which come from how chicks are fed.

5The surviving swallows raised their chicks under the bridge that summer. In the two years after the cold spell, the young adults returning to the colony had an average mass of 23.4 g. In the years before it, the average had been 22.9 g.