The Wilson Journal of Ornithology 123(3):508-514, 2011 
NOCTURNAL PROVISIONING BY SWAINSON’S THRUSH 
JEFFREY R. BALL, 1 - 3 KATRINA C. LUKIANCHUK, 17 AND ERIN M. BAYNE 1 
ABSTRACT. We studied Swainson's Thrush ( Catharus ustulatus) at two study areas of different latitudes lo eumme 
if parents provisioned their nestlings beyond daylight hours. We viewed 591 hrs of video from 37 nests. All nests were 
provisioned outside the dawn to dusk period but provisioning also continued through the night at the northern site. Nieht 
E— “f" aVCrag h e ( - SE) of 155 ~ 01 « fewer provisioning ,rips/hr during die pre-dawn to late evenL 
E n SJTS fT, V, ^ nCrS - Nigh ‘ pr ° Visi0ners c <> m Pensatcd with two additional trips/hr during the post"- 
reDrod!crive d s w k ’ trips/hr durin £ ,he ni S hl P eriod - Night provis,oners did not experience improved 
NHt nmvT 8 ' which supports our conclusion that night provisioning was compensatory rather than W enen, 
oericSZ'r'h? r St eXpla,ned by increased di, y le "Sth. which corresponded to increased light levelsdunne At 
met E as • Pare0tS ,0 TT ^ ,OCate f00d - Swai "-"’ s Thntsh extend a given provisioning efforts 
en e v for ot t it " » Z ^ dcliv ^ ,0 lhdr nestlings which may provide time and 
energy for other activities. Received 27 August 2010. Accepted 18 January 2011. 
Foraging and acquisition of energy are impor¬ 
tant to animal survival. However, energy acqui¬ 
sition often conflicts with other activities that arc 
important components of fitness including avoid¬ 
ing predators (Lima and Dill 1990). provisioning 
dependent young (Ydcnberg 1994), and maintain¬ 
ing social bonds (Dunbar et al. 2009). Individuals 
are expected to tradeoff foraging with other 
fitness related activities subject to ensuring their 
energy needs are met (Houston and McNamara 
1985 1999; Dunbar et al. 2009). The decision to 
spend time on alternate activities depends, in part, 
on the individual’s current energy state and time 
available to acquire sufficient resources to survive 
^extended period of forced fasting (Stephens 
The active period of songbirds is assumed to be 
largely restricted to daytime hours (i.e., between 
dawn and dusk) when the available light affords 
the visual acuity necessary to perform complex 
tasks such as navigating and locating food 
Individuals able to extend the length of their 
active period would have an advantage in 
balancing energy acquisition with other activities. 
The intensity and duration of light available 
outside of daytime hours varies considerably over 
space and time depending on moon phase, cloud 
^QQm a v Py C ,° Ver ’ Und date and la,i,ude (Martin 
1990). Visual acuity increases with light avail¬ 
ability and individuals in open habitats at high 
Tiucgi-ated Landscape Management Group, CW -405 
u " ivcr '“ y of Alb ™- 
C *f mmen ' of Biological Sciences 
Corresponding author; e-mail; jball@ua!berta.ca 
latitudes during the summer solstice with a full 
moon under clear sky conditions have the greatest 
potential to extend the length of their active 
period. 
Additional active time allows parents with 
dependent young more opportunity to meet (heir 
energy needs and the energy needs of their brood 
(Ydenberg 1994). Parents may use additional 
foraging time to compensate for an energy shortfall 
due to poor food quality. low food abundance, 
inclement weather (McCarty and Winkler 1999), 
and/or to avoid predation risk (Eggers et al. 2005) 
during day-time hours. Extending the active period 
could also allow parents time to provide additional 
bonus energy to their nestlings, which could lead 
to larger broods (Drent and Daan 1980). increased 
growth rates, a shortened pre-fledging period 
(Searcy et al. 2004), and improved probability nl 
surviving post-fledging (Monros et a!. 2002) 
Wc studied nestling provisioning rates by 
parent Swainson’s Thrush (Catharus ustulatus ) 
at two study areas of different latitude to examine 
(I) if hourly provisioning rates during the day and 
night varied between study areas; (2) if nocturnal 
provisioned fed their nestlings at lower rates 
during the day; (3) what factors were associated 
with variation in nocturnal provisioning rate; and 
(4) if nocturnal provisioning improved reproduc¬ 
tive success. 
508 
METHODS 
Study Area. —We established 15 plots in mature 
mixedwood forest in two study sites in the boreal 
forest of western Canada. Six 42-ha plots were 
near Fort Simpson, Northwest Territories (61 52' 
N, 121 20' W) in 2005 and 2006, and nine 24-ha 
plots were in the Chinchaga forestry region 
