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THE WILSON JOURNAL OF ORNITHOLOGY • Vo I. 124. No. 4. December 2012 
The Wilson Journal of Ornithology 124(4):808-81 I, 2012 
Effects of Conspecifics on Feeder Choice by Northern Cardinals 
David M. Millican,' Patrick G. McGovern,' and Mark T. Stanback 1 - 2 
ABSTRACT.—Inter- and intra-specific competition 
are known to influence feeding decisions, but relatively 
little research has investigated how inter- and intra- 
sexual interactions can impact foraging. We studied 
foraging preferences of male and female Northern 
Cardinals (Cardinalis cardinalis) during winter and 
found they preferred sunflower seed to safflower seed 
when presented with paired feeders in the absence of 
conspecifics. Male Cardinals avoided feeders occupied 
by other males and approached feeders occupied by 
females, regardless of feeder contents. Female cardinals 
avoided other females and especially males when 
choosing feeders. These changes in foraging behavior 
by male and female cardinals as a result of conspecific 
presence indicate inter- and intra-sexual interactions 
alter the attractiveness of a high or low energy food 
source. Received 27 December 2011. Accepted 7 June 
conspecifics altered the foraging behavior of male 
and female Northern Cardinals (Cardinalis car¬ 
dinalis) using feeders during winter. For example, 
males ot this species are known to be dominant to 
females during winter (Nice 1927. Laskey 1944, 
Rite hi son and Omer 1990,); thus we might expect 
males to monopolize preferred foods—if nutrition 
was their only consideration. We provided 
Northern Cardinals with paired feeders containing 
different foods (sunflower vs. safflower seed) to 
lest the extent to which their foraging decisions 
were influenced by the gender of other conspe¬ 
cifics present. 
METHODS 
Organisms must be discerning when presented 
with conflicting options regarding foraging (Sih 
1980. Lima and Dill 1990. Krebs and Kaeclink 
1991, Cuthill and Houston 1997). Individuals 
must optimize energy intake by trade-offs in 
both food quality and vulnerability to predation 
(Stanback and Powell 2010). Competition (both 
inter- and intra-specific) can also have a substan¬ 
tial impact on tbe ability of individuals to access 
food sources (Nice 1927. Lima and Dill 1990. 
Shedd 1990. Belthoff and Gauthreaux 1991 
Tarvin and Woolfenden 1997. Lima 1998. Rands 
et al. 2006). Finally, inter- and intra-sexual 
interactions, while often considered only in the 
context of breeding, can have dramatic effects on 
foraging in birds (Selander 1966. Schneider 
1984). Inter-sexual niche separation, for species 
that lack substantial morphological differences in 
trophic structures, often results from social 
dominance of one sex over the other (Desrochers 
1989, Hogstad 1991). It j s unclear, however, 
whether males and females can cleanly separate 
their foraging and sexual interactions, even durins 
winter. We investigated how the presence of 
NC 28036° USA f Bl ° IOgy ' Davidson Collc S e - Davidson, 
2 Corresponding author; 
e-mail: mastanback@davidson.edu 
l iehl Procedures .—Northern Cardinals are 
year-round residents in the southeastern United 
States and common visitors to feeders (Halkin and 
LinviHe 1999). Pair bonds typically dissolve 
dining the non-breeding season and cardinals in 
an area form loose flocks (Halkin and Linville 
1999). We observed Northern Cardinals between 
15 and 21 January 2010 at five locations on the 
Davidson College campus in Davidson. North 
Carolina, USA (35 30' N, 80 50' W). The five 
feeding sites were no closer than 500 tn from one 
another. We set up two pole-mounted Absolute 
hopper-style squirrel-proof bird feeders (1.5 m 
apart) at each site, labeled A and B. Feeders were 
kept filled lor 5 weeks prior to data collection. We 
filled one feeder with unshelled safflower seeds 
and the other with unshelled black-oil sunflower 
seeds, buth from Wild Birds Unlimited. The 
I ceding perch on each feeder was 29 cm long. 
Wc adjusted the feeders to accommodate the mass 
ol two cardinals, but cardinals rarely fed side by 
side. We used 7 x 35 Nikon binoculars to observe 
cardinals at feeders at each site for 1 hr twice a 
day. once before and once after 1200 hrs. fora total 
of 68 observation hours. We observed feeders 
Irom a distance of 30 m to avoid disturbing feeding 
individuals. We switched the position of the 
feeders at each site alter 3 days of observations to 
eliminate biases due to possible site preferences. 
