Problem Set 5
The following data and questions relate to a study clapper rails in two salt marshes on the Atlantic
coast of Connecticut. Birds were counted between sunrise and 2 hours after sunrise in July 2006 at 10
randomly located points in each of two marshes. A different point was sampled each day until all were
sampled once. All birds seen or heard within 50 m of the point were recorded, with the total number of
birds reported used as an estimate of rail abundance for that point. After completing bird counts, the
dominant habitat type (i.e., cordgrass, meadow, or mudflat) was visually determined at each point.
Then, invertebrates and small fish (i.e., potential rail foods) were sampled in a 1 m2 plot centered on
the point using a suction sampler, and water depth was recorded at the point location using a depth
gauge. The remainder of the day after the counts and other measurements was spent searching for rail
nests. When a nest was found, it was marked with flagging and the major habitat type and stage of
incubation (i.e., how many days until hatch) was determined. Nests were subsequently revisited 21
day after hatching to determine if nests were successful (i.e., hatched at least 1 egg) or not. The data
follows the questions.
1. Discuss any problems with the sampling described above.
2. Determine rail, invertebrate, and fish abundance ( ±SE) by habitat and marsh.
3. Determine if rail abundance varies by habitat type (do not be concerned with which marsh
points are in). If so, which habitat type has the highest and lowest abundances?
4. Determine if rail abundance differs between the 2 marshes using a parametric and a nonparametric test. Discuss differences in results.
5. Assume that different marshes will affect rail abundance, but you are not interested in this
marsh effect. Determine if rail abundance varies by habitat type. If so, which habitat type has
the highest and lowest abundances? Do these results differ from those in #3? Why?
6. Determine the effects of marsh and habitat type and the interaction of the two on rail
abundance. In which marsh, habitat, or marsh*habitat type are rails most and least abundant?
Why not? How do these results differ from #3 and #5?
7. Determine if invertebrate abundance effects rail abundance.
8. Determine which combination of variables (i.e., water depth, and invertebrate and fish
abundance) best predicts rail abundance. How did this differ from #7?
9. Determine if and how invertebrate abundance is correlated with fish abundance.
10. Determine if rail nest success depends on which habitat type the nest is in (use chi-square and
likelihood ratio statistics). Which habitat has the highest and lowest nest success?
Answers to questions should always include both results and discussion. Results should include that
test used, ±SE or % for groups being compared, units, p-values, regression equations, r, and r2, etc.
Unless it is otherwise specified, always use default computer settings, parametric tests, equal
variances, forward procedures, least squares procedures, fixed factors, P ≤ 0.05, and Fishers LSD
procedures.
Point
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Nest
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
Marsh
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
Habitat
cordgrass
cordgrass
cordgrass
cordgrass
cordgrass
cordgrass
cordgrass
cordgrass
cordgrass
cordgrass
cordgrass
mudflat
mudflat
mudflat
mudflat
mudflat
mudflat
mudflat
mudflat
mudflat
mudflat
mudflat
mudflat
mudflat
mudflat
mudflat
Habitat
cordgrass
meadow
mudflat
cordgrass
meadow
mudflat
cordgrass
meadow
mudflat
cordgrass
meadow
mudflat
cordgrass
meadow
mudflat
cordgrass
meadow
mudflat
cordgrass
meadow
Successful
y
y
y
y
y
y
y
y
n
n
n
n
n
n
n
n
n
n
n
n
y
y
y
y
y
y
Rail
Abundance
(#)
12
5
1
8
6
1
9
8
1
7
8
4
9
5
2
8
6
3
7
2
Invert.
Abundance
(#/m2)
10
5
2
10
5
3
8
7
2
8
6
2
10
6
3
9
6
3
7
3
Fish
Abundance
(#/m2)
3
5
9
3
6
9
1
2
8
2
5
9
1
6
10
2
5
8
1
4
Water
depth
(cm)
2
6
8
3
6
4
7
9
2
5
9
4
6
9
1
3
6
4
8
3