Allen and Peters • COMMON NIGHTHAWK NESTING BIOLOGY 
117 
(i.e„ >20 nests; Hensler and Nichols 1981), which 
is reflected by the wide confidence intervals around 
these estimates (48-93% incubation .survival for 
nur study, and 11-68% in Perkins and Vickery 
2007). We found apparent nest survival (i.e., % 
successful nests) of 81% (13 of 16 nests) in 
comparison to 93% in grasslands of the northern 
Great Plains (13 of 14 nests [excluding 1 human- 
induced failure): Kantrud and Higgins 1992). and 
43% in Florida dry prairie (6 of 14; Perkins and 
Vickery 2007). Neither Kantrud and Higgins 
1 1992) nor Perkins and Vickery (2007) reported 
nest abandonment and both concluded that preda¬ 
tion was the main cause of nest failure. 
Published studies of Common Nighthawks have 
considered only nest survival through hatching. A 
complete picture of nest survival requires data for 
the period of young development. Including this 
■uage would necessarily result in lower estimates 
of overall success, If we assumed, for example, 
the same daily survival rate for the period of 
young development as we found for incubation, 
the expected probability of survival to fledging at 
our site would be 62% (assuming 18 days front 
hatching until Hedging; Brigham et al. 2011). The 
question of whether survival differs substantially 
between eggs and pre-fledged young in Ibis 
species will likely require telemetry data due to 
ihe uncertainties associated with monitoring semi- 
precocial young (e.g., Fowle 1946, Rust 1947. 
Perkins and Vickery 2007). 
Clutch size of Common Nighthawks is similar 
across a broad geographic area with two-egg 
clutches dominant in Idaho (24 of 27 clutches; 
Rust 1947), the northern Great Plains (18 of 21; 
Kantrud and Higgins 1992). New Jersey (16 of 17; 
ihis study), and Florida (13 of 14; Perkins and 
Vickery 2007). All other clutches consisted of one 
e t'g- Perkins and Vickery (2007) argued that some 
one-egg clutches could be the result of partial 
depredation, and both Rust (1947 ) and Sutton and 
Spencer (1949) observed eggs rolling from nests 
w hen ihe female flushed, which could be another 
source of clutch reduction. We observed one nest 
la 2-egg clutch) at which the second egg was not 
incubated, but was found •— 1 m distant. 
The movements of young we recorded were 
similar to previous reports for both rooftop and 
non-rooftop sites (Fowle 1946. Rust 1947, Dexter 
1952). Fowle (1946) reported single-day move- 
ments as far as 15-27 m in a burned clear-cut on 
Vancouver Island. British Columbia, compared to 
'he maximum of 6 m in 2 days in our study. It is 
possible that Fowle’s handling of young for 
weighing (not done in our study) contributed to 
the farther single-day movements he observed. 
Few data exist on the habitat preferences of 
Common Nighthawks. However, our finding that 
open ground was preferred is not surprising based 
on several qualitative accounts (e.g., Fowle 1946, 
Rust 1947. Brigham et al. 2011) and two 
quantitative studies (Kantrud and Higgins 1992, 
Lohnes 2010). Typical nesi sites in our study were 
in patches of ‘open’ ground (e.g., sand, lichens, 
litter), between warm-season grasses or erica- 
ceous shrubs that often provided partial shade. 
Lohnes (2010) compared nest sites with random 
areas in the Konza Prairie in Kansas and also 
found a preference for open ground. Kantrud 
and Higgins (1992) noted that over half of 21 
Common Nighthawk nests in the northern Great 
Plains had 'no vegetation' and they report an 
average vegetation height ot 6 cm, considerably 
lower than that of other ground-nesting birds in 
the area (mean = 33 cm). We found mean 
vegetation height at nest sites to be about half that 
of random areas (10 vs. 22 cm), a discrepancy at 
least partly driven by the higher number of zero 
height values at nest sites in open areas. 
The pattern of nest-initiation dates observed 
in our study appeared to be unimodal (Fig. 2), 
although it is possible that increased sample sizes 
would reveal a different pattern. Some nests also 
may have been initiated before or after nest 
searches (15-28 Apr to 15 Jul). This is not likely 
to be a significant proportion of nests, however, as 
nighthawks do not typically arrive on the study 
site until early to mid-May (MCA, pers. obs.) and 
fall migration in this species begins in mid-August 
(Walsh et al. 1999). The median initiation date we 
observed (31 May) was earlier than observed in 
the northern Great Plains (24 Jun, n = 8 nests, 
Kantrud and Higgins 1992) and northern Idaho 
(30 Jun, n = 27; Rust 1947), hut our range (18 
May-28 Jun) was within the range observed in 
these studies (7 May-15 Jul). 
ACKNOWLEDGMENTS 
This study w as funded by the Department of Defense 
Legacy Resource Management Program and ihe U.S. Navy 
Agricultural Outlease Program. Field work was performed 
by Mike Allen. Ron Hutchison. Tamarra Mart/, Kim Peters, 
Ben Sandstrom. Katie Schill. I.ena Usyk, and Rachel 
Villani. We thank John Joyce of Joint Base McGuire- 
Dix-Lakehurst for helpful logistical support. 
