SHORT COMMUNICATIONS 
793 
The Wilson Journal of Ornithology 124(4):793—797. 2012 
Growth Rate and Relocation Movements of Common 
Nighthawk (Chordeiles minor) Nestlings in 
Relation to Age 
Gunnar R. Kramer 1 * - 3 and Anna D. Chalfoun 12 
ABSTRACT.—Relocation by dependent young ts a 
survival strategy that occurs among a wide range of 
laxa. The Common Nighthaw k (Chordeiles minor) lays 
its eggs on bare substrate and. once hatched, nestlings 
may relocate to new sites daily. We located and 
monitored eight Common Nighthawk nests in Grand 
Teton National Park. Wyoming, quantified intcr-use- 
site distances in relation to nestling age, and calculated 
a nestling growth rate curve. Common Nighthawk 
nestlings grow in a nearly linear fashion. Nestlings 
moved up to 48 m in a single day and larger, older 
nestlings tended to move greater distances between 
daily use-sites. Received 2 December 21)11. Accepted 25 
hme 2012. 
Life history traits, including successful predator 
avoidance behaviors by young, which promote 
juvenile survival, should increase an organism’s 
fitness and be favored by natural selection (Roff 
1992). Relocation of dependent offspring to 
increase the probability of survival is a tactic that 
occurs in a broad range of taxa. However, the 
ability of the non-precociul young of most avian 
species to change their location is limited, 
primarily due to construction of often elaborate, 
stationary nests where they are fed and brooded 
b\ adults (Collias and Collias 1984. Podulka et al. 
2004). Relocation of young birds to limit 
predation risk, while reasonable, is poorly docu¬ 
mented. Moreover, the details of this strategy in 
avian species rearing dependent young remain 
largely unknown. 
Many species of nightjars (Caprimulgidae) 
have semi-precocial nestlings hatched from eggs 
laid on bare ground (Holyoak 2001) without creat¬ 
ing any nest structure. Anecdotal observations 
suggest Common Nighthawks ( Chordeiles minor) 
1 Department of Zoology and Physiology. I niversity of 
Wyoming. Laramie. WY 82071, USA. 
3 U.S. Geological Survey. Wyoming Cooperative Fish 
and Wildlife Research Unit. Department 3166. 1000 East 
University Avenue. Laramie. WY 82071. USA. 
Corresponding author; e-mail: 
gunnarrkramer@gmail.com 
move their eggs and coax their pre-fledge. semi- 
precocial nestlings to move in response to 
disturbance both by potential predators and 
rnicrohabitat disturbances such as pooling water 
(Pickwell and Smith 1938; Fowle 1946: Rust 
1947; Sutton and Spencer 1949: Dexter 1952, 
1961; Weller 1958; Brigham et al. 2011). 
However, factors influencing the distance and 
frequency of pre-tledging chick movements are 
unclear. We tested the hypothesis that nighthawk 
nestlings' movements between daily use-sites 
increase with offspring age. We also calculated 
a Common Nighthawk nestling growth rate curve 
using, for the first time, measurements obtained 
from multiple chicks and broods. 
METHODS 
Study Area and Field Techniques.— Our study 
occurred during May-August 2010 within sage¬ 
brush (Artemisia spp.) Hats in Grand Teton 
National Park, northwestern Wyoming. Elevation 
ranged from ~ 1,950 to 2.012 m and sites were 
dominated by mountain big sagebrush (A. triden- 
tata vaseyana). Nighthawk nests were located by 
chance during systematic searches for nests ol 
shrub and ground-nesling passerines. 
Common Nighthawk nests and use-sites were 
cheeked daily between 1400 and 2000 hrs MST, 
barring inclement weather. We navigated to the 
most recent known daily use-site using u handheld 
global positioning system (GPS) and attempted to 
relocate nestlings by initially searching within a 
10-m radius from that point. We returned to the 
most recent known use-site if the nestlings were 
not relocated during the initial 10-m radius search 
and walked four 50 m by 50 m quadrants centered 
at the last known use-site, effectively searching an 
area of 1,000 nr. We repeated the quadrant search 
on each of the 2 days following the initial 
disappearance of the nestlings and assumed the 
nest was no longer active or had moved out ol our 
search radius if we were still unable to locate the 
brood. We Hushed the brooding female upon 
