That Remarkable Peterson Entrance
Wayne H. Davis
When given a choice, Eastern Bluebirds (Sialia sialis) have a strong
preference for the Peterson box over various other styles (Berner, 1995;
Davis and Kalisz, 1995; Palahniuk and Bakko, 1995). 1 have shown that an
important component of this preference is the unique Peterson entrance 2
1/2 inches (55 mm) high and 1 3/8 inches (35 mm) wide, made by drilling
two overlapping holes with a 1 3/8 inch bit. I alternated boxes with
slot entrances and Peterson entrances and found a tendency of bluebirds
to choose the Peterson entrances and House Sparrows (Passer domesticus)
to take the boxes with the slot entrances (Davis, 1995).
To improve the experimental design 48 and give the birds a sharper
choice, I modified this experiment for the 1996 season. In October 1995,
1 cleaned out all the boxes and moved boxes so as to have one of each
style, facing opposite directions mounted on a conduit. Thus, instead of
100 stations, I now had 50, each with two boxes. To avoid bias from the
previous usage, I alternated which style of box was to be moved.
I checked the boxes in March and began monitoring at two week
intervals in April. A box was recorded as used when it contained a nest
and one or more eggs. Bluebirds used eight of the Peterson entrance
boxes and four of the slot, a ratio similar to that of the previous
year. House Sparrows used 27 slot boxes and only two with the Peterson
entrance, a sharper difference than the previous year.
Table 1. Choice of entrance style.
| |
used by
bluebirds |
used by
sparrows |
used by
swallows |
| Peterson |
8 |
2 |
0 |
| slot |
4 |
27 |
1 |
House Sparrows and Eastern Bluebirds show a striking difference in
preference of entrance style. Sparrows prefer a round hole to a slot
(Davis, 1989), and the slot to the Peterson entrance, whereas bluebirds
prefer the Peterson entrance to the slot, and the slot to the round hole
(McComb, eta/., 1987). These differences are so striking that anyone
building new boxes should consider making the Peterson entrance.
A potential problem with the Peterson entrance is that it is readily
accessible to European Starlings (Sturnis vulgaris). Starlings explored
my boxes but did not use any of them, probably because they are rather
shallow (5 inches; 12.5 cm) with a small floor (4 x 3 1/2 inches; 10 x
8.8 cm). With a deep, roomy box you can expect problems with starlings.
Kridler (1990) built six deep, roomy boxes with Peterson entrances and
had all of them used by starlings. To make a Peterson type of entrance
that is not accessible to starlings you would need to use a 1 1/8 inch
(30 mm) bit.
Literature Cites
