Dry Ponds, Wet Years: Arguing About a Prairie Refuge

Use refuge surveys to argue how drought and fish changed animal populations.

Answer Key

Seven years of surveys

Read the passage and study Table 1. Then answer the questions.

Counting at Sandhill Lakes

1Sandhill Lakes Wildlife Refuge protects a rolling grassland dotted with 40 small ponds called prairie potholes. Snowmelt and spring rain fill the ponds, and many of the shallow ones dry up by late summer. In a dry year, some never fill at all. Every year, refuge biologist Dr. Thaddeus Kowalczyk leads volunteers from Prairie View Middle School on wildlife surveys. This year, seventh grader Marisol Etsitty helped him look back over the records from 2019 to 2025 to see how the refuge's animals had changed.

2Ducks such as mallards and blue-winged teal fly north in spring. A pair settles where it finds ponds with water, nests in the tall grass nearby, and leads its ducklings to the water to feed on insects. Each May, volunteers count the ponds holding water and the duck pairs on the refuge. Muskrats are a different story. These large rodents live in the same deeper ponds all year, eat mostly cattails and other water plants, and build dome-shaped lodges out of cattail stems. A muskrat family usually raises its young in summer. Each October, volunteers count the lodges (Table 1).

3In 2024, Marisol joined a frog survey. Chorus frogs lay their eggs in the ponds in early spring, and the tadpoles take about 6 to 8 weeks to change into young frogs that can live on land. Her class picked eight ponds where eggs had been laid in April. They recorded how many weeks each pond held water after the eggs were laid, and in early summer they searched each pond's edge for 10 minutes and counted the young frogs (Graph 1). The survey season lasted 20 weeks, and Ponds G and H held water the whole time.

4Pond H is the only pond in the study with fish. Someone released fathead minnows there several years ago. These small fish eat insects, frog eggs and tadpoles. The other seven ponds have no fish, because ponds that dry out every few years cannot keep fish alive.

Table 1. Refuge Surveys, 2019–2025 (the refuge has 40 ponds)
Year	Rain, last 12 mo. (cm)	Ponds with water, May	Duck pairs	Muskrat lodges
2019	46	33	300	21
2020	44	31	280	22
2021	27	15	130	12
2022	22	8	60	4
2023	49	30	270	3
2024	52	34	310	7
2025	47	32	290	13

How many fewer duck pairs were counted in 2022 than in 2020? 220 pairs

In 2024, about how many duck pairs were there for each pond holding water? Round to the nearest whole number. 9 pairs per pond

Which argument about the duck pairs do the passage and Table 1 support best?

A. Duck pairs rose and fell with the number of ponds that held water in May.
B. Duck pairs went down steadily from 2019 to 2025 as the ponds slowly filled in.
C. Duck pairs fell in 2021 and 2022 because the muskrats ate many of the ducks’ eggs.
D. Duck pairs stayed near 300 each year, so the drought did not change the refuge’s ducks.

By 2023, the rain, the ponds and the duck pairs were back near their 2019 levels. Yet only 3 muskrat lodges were counted. Which explanation fits the passage and Table 1 best?

A. Muskrats feed mostly on duck eggs, so they could not grow until the ducks came back.
B. Muskrats build more lodges in dry years, when the cattails are easiest to reach on foot.
C. Ducks fly in from elsewhere, but muskrats stay all year and needed years to rebuild.
D. Muskrats compete with ducks for cattails, so they left once the ducks came back.

Frogs, drying ponds and fish

Use paragraphs 3 and 4 and Graph 1. Each point is one pond, labeled with its letter.

Graph 1. Chorus frog survey, 2024. Across: weeks the pond held water after the eggs were laid. Up: young frogs found in a 10-minute search. Pond H is the only pond with fish.

Which pattern does Graph 1 show for the seven ponds without fish?

A. Ponds that held water for 2 to 4 weeks had the most young frogs.
B. Young frogs rose from 0 at 2 weeks of water to 18 at 20 weeks.
C. Each pond had about 10 young frogs, whatever its weeks of water.
D. Young frogs rose to a peak at 8 weeks of water and then fell to 2.

No young frogs were found at Ponds A and B. Which explanation fits paragraph 3 and Graph 1 best?

A. The ponds dried up before the tadpoles had time to change into frogs.
B. Fathead minnows in Ponds A and B ate the frog eggs before they hatched.
C. The ponds held water so long that the tadpoles stayed in the water.
D. Young frogs had already left those ponds, since they changed faster there.

Ponds G and H both held water for 20 weeks. How many more young frogs were found at Pond G than at Pond H? 16 frogs

Which argument about Pond H do paragraph 4 and Graph 1 support best?

A. Pond H had the most young frogs, because fish keep the water clean for tadpoles.
B. Pond H dried out in early summer, so its tadpoles had too little time to change.
C. Young frogs in Pond H hid from the minnows in the grass, so the class could not see them.
D. Minnows likely ate many eggs and tadpoles, since Pond G held water as long.

Suppose a dry spring leaves most refuge ponds holding water for only 4 to 6 weeks after the eggs are laid. Which prediction about the chorus frogs does the evidence support best?

A. About the same number of young frogs as in 2024, since the frogs lay the same number of eggs.
B. Far fewer young frogs than in 2024, since most ponds would dry before the tadpoles change.
C. More young frogs in Pond H than in any other pond, since its minnows would leave in a drought.
D. Many more young frogs than in 2024, since a short pond season leaves no time for predators.

Build the argument

Use Table 1, Graph 1 and the passage.

10.

Sort each statement about the refuge.

Fewer ponds held water in May in the years with less rain.Duck pairs fell in 2021 and 2022 because hunters took more ducks.Muskrat lodges were still below their 2020 count two years after the rain returned.Fish in a long-lasting pond can keep most tadpoles from becoming frogs.Ponds that dried within 4 weeks produced the most young frogs.Muskrats moved into Pond H during the drought to eat its minnows.

Supported by the refuge data	Not supported by the refuge data
Fewer ponds held water in May in the years with less rain. Muskrat lodges were still below their 2020 count two years after the rain returned. Fish in a long-lasting pond can keep most tadpoles from becoming frogs.	Duck pairs fell in 2021 and 2022 because hunters took more ducks. Ponds that dried within 4 weeks produced the most young frogs. Muskrats moved into Pond H during the drought to eat its minnows.

11.

A refuge visitor says, “Once the rain came back in 2023, every animal population at Sandhill Lakes was back to normal.” Write an argument for or against this claim. Make a claim, use evidence from Table 1 and Graph 1, and explain how a change to a physical or living part of the ecosystem affected at least two populations.

Claim: The visitor is wrong; not every population was back to normal in 2023. Evidence: the drought was a change to a physical part of the ecosystem. Rain fell from 44 cm in 2020 to 22 cm in 2022, and ponds with water dropped from 31 to 8. Duck pairs fell from 280 to 60, but they rose to 270 in 2023 when 30 ponds held water again, so the ducks did recover quickly. Muskrat lodges fell from 22 to 4 and were only 3 in 2023, 7 in 2024 and 13 in 2025, still below the 21 to 22 of 2019 and 2020. Graph 1 also shows that frogs depend on how long ponds hold water: ponds that held water 2 or 4 weeks had no young frogs, while ponds that held water 16 or 20 weeks had 16 or 18, and the pond with fish had only 2. Reasoning: ducks fly in each spring and settle wherever there is water, so their numbers follow the ponds right away. Muskrats live in the ponds all year, so when many died in the drought, the few left needed years to raise enough young to rebuild. A physical change can affect populations for years after it ends, and a living change like fish in a pond can cut a population even when water is plentiful.