Forsman et al. Appendix A
Appendix A. Explanation of annual variation in experimental setup and testing its
effect on response variables.
There was some minor variation in experimental details between years due to other
concurring studies, in the number of available boxes per site and occurrence of novel
nest-site preferences (abstract symbols) on boxes [see 1]. However, the main element and
assumption of the design was the same in both years: simulated low and high tit clutch
size reflect poor and high quality territory, respectively, and seek to answer the question
whether flycatchers use tit clutch size as a cue about the territory quality and in offspring
investment decisions.
In 2009, each site included two pairs of boxes with geometric symbols attached, and sites
were at least one kilometer apart (symbols and the site separation distance were not
related to hypothesis addressed here, for details of the concurring other study see [1]).
Boxes within a pair were in the immediate vicinity (3-5 m), while the distance between
box pairs was about 30 m. One of the four boxes included a simulated tit nest, while other
boxes were clean.
In 2010, experiment focused solely on the investment hypothesis, and sites were at
minimum 400 m apart, each site including just two nest boxes 30 m apart. One of the
boxes included a simulated great tit nest, and the other box had no material. The 2009
experiment had shown that flycatchers settling at the experimental sites usually nest on
Forsman et al. Appendix A
top of simulated (and hence unguarded) tit nests, but an empty nest box was retained in
the experiment design to provide similar opportunity to choose an empty box.
The effect of year and variation in experimental set-up on response variables, and
whether pooling data across years was justified, was tested by a t-test.
There were no statistically significant differences between years in clutch size (mean =
6.31, t = 1.75, df = 78, P = 0.084), average mass of the egg (mean = 1.33, t = 0.01, df =
74, P = 0.991) and mass of the clutch (mean = 6.32, t = 1.12, df = 74, P = 0.246). In 2009,
68.9% of the flycatchers bred on top of the simulated tit nest, and 29.4% in one of two
empty boxes 30m away from the tit nest, and only 1.7% (one pair) in the box adjacent to
the simulated tit nest [1]. In 2010, only two females (5.3%) chose to nest in the empty
box. This result is similar to the findings of Forsman & Seppänen [1] and we conclude
that all else being equal (i.e., without additional information to base decisions on),
flycatchers prefer to nest on top of tit nests.
Breeding either on the simulated tit nest or in an empty nest box did not affect the clutch
size (t = 1.19, df = 41, P = 0.237), egg mass (t = 0.25, df = 41, P = 0.804) or clutch
biomass (t = 1.01, df = 41, P = 0.319). These results show that the slight variation in the
experimental details between years did not affect the main response variables of the
present study and pooling data across years is therefore justified.
REFERENCES
Forsman et al. Appendix A
1 Forsman, J. T. & Seppänen, J.-T. 2011 Learning what (not) to do: testing rejection and
copying of heterospecific behavioural trait. An. Behav. 81, 879-883.