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THE WILSON JOURNAL OF ORNITHOLOGY . Vol. 123. No. 3. September 2011 
monogamous and males likely can be certain of 
their paternity and may not seek exlrapair 
copulations. Thus, providing parental care may 
be a better strategy for males to maximize 
reproductive success than seeking additional 
mating opportunities. 
Several factors may influence provisioning 
behavior of male Grasshopper Sparrows. For 
example, nest predation rates for this species are 
typically high (50-75%) (Vickery 1996) and. as 
suggested for Willow Warblers (Bjornstad and 
Lifjeld 1996). provisioning by males may help 
insure rapid growth of nestlings, earlier fledging, 
and reduced risk of nest predation. In addition. 
Grasshopper Sparrows are typically multi-brooded 
and. as suggested for Black-throated Blue Warblers 
(Dendroica cuerulescens) (Stodola et al. 2009), 
males may improve their reproductive success by 
provisioning nestlings in first broods to increase the 
likelihood ol mates subsequently re-nesting. 
Provisioning rates and amount of biomass 
delivered to nestlings by Grasshopper Sparrows 
in our study increased until day 6 and decreased 
prior to fledging (days 7-10 post-hatching). 
Similar variation in provisioning behavior has 
been reported in other songbirds, including 
European Robins (Erithacus rubecula) (East 
1981) and Savannah Sparrows (Passerculus 
sanwichensis ) (Bedard and Meunier 1983). Adult 
provisioning rates of other songbirds continue to 
increase with nestling age and are highest just 
before fledging (e.g., Grundel 1987, Goodhred 
and Holmes 1996. Yezerinae et al. 1996, Filliater 
and Breitwisch 1997). Goodbred and Holmes 
(1996) suggested a positive relationship between 
nestling age and provisioning rate was due to 
increasing energy demands of the young, either 
for growth or thermoregulation. 
The decline in provisioning rates of adult 
Grasshopper Sparrows near the end of the nestling 
period may be influenced by the risk of nest 
predation with adults encouraging or inducing 
fledging by reducing provisioning rates. Nestling 
Grasshopper Sparrows may leave nests to obtain 
food from adults approaching the nest (Young 
1987), suggesting that inducing older nestlings to 
fledge may not be difficult. Young Grasshopper 
Sparrows are generally unable to fly when they 
first leave nests but are able to run (Smith 1963); 
mobile young able to run and hide in vegetation 
may be less susceptible to predation. The chances 
o an entire brood being lost to predation would 
likely be reduced once young have fledged. 
Provisioning rates and amount of biomass 
delivered by adult Grasshopper Sparrows in¬ 
creased with increasing brood size. Thus, individ¬ 
ual nestlings in broods of different size were 
provisioned at similar rates and received similar 
amounts of prey biomass. Kaspari (1991) studied 
a population of Grasshopper Sparrows in Ne¬ 
braska and reported similar results. Provisioning 
ol individual nestlings at similar rates, regardless 
of brood size, may enhance the reproductive 
success of adult Grasshopper Sparrows because 
mass at fledging is an important predictor of 
survival for young (Magrath 1991, Ringsbyetal. 
1998, Schwagmeyer and Mock 2008). 
Our sample size for second nests was small In 
= 4) and we found no effect of nest number (first 
vs. second) on the provisioning behavior of 
Grasshopper Sparrows. Similar results have been 
reported for other species of .songbirds (e.g.. 
MacColl and Hatchwell 2003, Nordlund and 
Barber 2005). Other investigators have reported 
lower provisioning rates for later broods (Royama 
1966. Barba et al. 2009), although Stodola et al. 
(2009) reported provisioning rates for second 
broods may be higher than for first broods. 
Grasshoppers were the most common prey 
delivered to nestlings with Lepidopteran larvae 
being the second most common. Kaspari and 
Joern (1993) reported similar results for Grass¬ 
hopper Sparrows in Nebraska. They also exam¬ 
ined the food habits of adult Grasshopper 
Sparrows and found that adults fed more on seeds 
and beetles than nestlings. Adults were also 
selective in the size of grasshoppers fed to 
nestlings with most being 15-35 mm in length 
(Kaspari and Joern 1993). 
About 90% of the identified prey items fed to 
nestling Grasshopper Sparrows in our study were 
grasshoppers (68.1%) and insect larvae (22.6% i- 
The energetic value of different arthropods is 
largely affected by their chitin content because 
chitin is largely indigestible (Karasov 1990. 
Klasing 1998 ). Larvae have a relatively low chitin 
content, while grasshoppers and other orthoptcr 
ans have a much higher percentage of chitin 
(Kaspari 1991). and tend to have lower energetic 
value. Adult Grasshopper Sparrows minimize the 
chitin content of orthopteran prey delivered to 
nestlings by: (1) usually removing parts that 
contain the most chitin, such as legs (Kaspan 
1990), and (2) usually feeding nestlings grass¬ 
hoppers between 15 and 35 mm in length (Kaspari 
and Joern 1993, our study). This is likely 
