Some bird species do not build nests and do not raise their own young.  Instead, they lay their eggs in the nests of other "host" birds. In this country, the cowbird is the most common bird that will do this.  In general, these  types of birds are known as brood parasites.  Due to the size differences and early hatching ability of the parasitic bird, the hosts raise only the young of the parasitic bird, thereby loosing their own clutch.  It is somewhat comical to see a small bird such as a sparrow or a finch feeding its much larger "adopted" baby.   To see a picture of a large cowbird egg in a nest of other smaller birds click here.  To see a small host bird feeding a cowbird click here.

Cuckoos are another species of brood parasites.  The data set that can be found here contains the length of cuckoo eggs that were found in nests of various other host birds. (Reference: L.H.C. Tippett, The Methods of Statistics, 4th Edition, John Wiley and Sons, Inc., 1952, p. 176.) The host birds represented are the Tree Pipit, Hedge Sparrow, Robin, Pied Wagtail, and Wren. All data are lengths in millimeters.

Copy the data into Minitab and do the following.

1. Make side-by-side boxplots of the lengths. (Graph > Boxplots > Multiple Y's Simple.)  By looking at the boxplots, does it appear that the mean lengths of the cuckoo's eggs vary depending on the host bird?

2. Let's look at the assumptions for completing and ANOVA.
1. The populations must be normal. To check this, complete a normal probability plot for each host bird type. (Graph > Probability Plot > Single) Are there any plots that indicate that we may not have a normal population? Include only those plots in your report that indicate the population may not be normal.  (Remember that the distribution could be considered normal if most of the points lie within the confidence bands on the probability plot.)
2. Find the sample standard deviations for each host bird type. Are these sample standard deviations within the limits of completing an ANOVA? Explain.

3. Complete an ANOVA for the mean lengths for the five different host birds. (Stat > ANOVA > One way (Unstacked)) then put all five species into the Responses window.) Make sure you write out your hypotheses, give your test statistic and P-value, and write out your conclusion.

4. Eliminate the sample that has lengths most different from the others and run another ANOVA. What is your conclusion this time?