The Wilson Journal of Ornithology 123(4):779-787, 2011 
INNATE IMMUNE RESPONSE DEVELOPMENT IN NESTLING 
TREE SWALLOWS 
TAMMY STAMBAUGH, 1 BRADLEY J. HOUDEK, 1 MICHAEL P. LOMBARDO, 13 
PATRICK A. THORPE, 1 AND D. CALDWELL HAHN 2 
ABSTRACT.—We tracked the development of innate immunity in nestling Tree Swallows {.Tachycineta bicolor) and 
compared it to that of adults using blood drawn from nestlings during days 6, 12, and 18 of the ~20-day nestling period and 
from adults. Innate immunity was characterized using an in vitro assay of the ability of whole blood to kill Escherichia coli. 
The ability of whole blood to kill E. coli increased as nestlings matured. Neither this component of innate immunity nor 
nght wing chord length on day 18 were as developed as in adults indicating that development of the innate immune system 
and growth both continued after fledging. Narrow sense herilability analyses suggest that females with strong immune 
responses produced nestlings with strong immune responses. These data suggest nestling Tree Swallows allocated sufficient 
energy to support rapid growth to enable fledging by day 18, but that further development of innate immunity occurred 
post-fledging. Received 22 December 2010. Accepted 21 May 2011. 
Ecoimmunology seeks to understand immune 
defense strategies observed among and within 
species in their natural environments (Martin et al. 
2011). One area of interest is developmental 
ecoimmunology (Apanius 1998). which investi¬ 
gates how a species' niche and life history 
strategy influence the rate and pattern of matura¬ 
tion of immune defenses (Sheldon and Verhulst 
1996. Norris and Evans 2000). The strength of 
immune responses is generally positively corre¬ 
lated with yearly survival for birds (Horuk et al. 
'"y. Christie et al. 2001, Ardia et al. 2003, 
Moller and Saino 2004), but the energetic costs of 
activating and maintaining the immune system 
may negatively affect growth (e.g., Mauck et al. 
2005, van der Most et al. 2011). 
Young birds, after hatching, primarily use 
innate immune defenses if infected by a pathogen 
'Apanius 1998, Bar-Shira and Friedman 2006), 
because adaptive immune responses do not 
develop until exposure to foreign antigens (Roitt 
et al. 1998). Innate immunity, the first-line of 
Jelense. is a fast-acting nonspecific response to 
Pathogens (Roitt et al. 1998). Young birds also 
depend on maternally-transferred antibodies 
'Hdleret al. 1990, Hahn et al. 2006. Hasselquisl 
“ttd Nilsson 2009) produced by their mothers in 
tevponse to exposure to foreign antigens, as well 
a v antimicrobial peptides (Ardia et al. 2011), 
another immune element provided in eggs. 
Resiling altricial birds, while confined to the nest 
Apartment of Biology. Grand Valley State University, 
Allendale. Ml 49401, USA. 
d.S. Geological Survey, Patuxent Wildlife Research 
te nter, 12100 Beech Forest Road, Laurel, MD 20708, USA. 
’Corresponding author; e-mail: lombardm@gvsu.edu 
and have bare skin before their feathers grow in 
and cover them, are exposed to disease organisms 
vectored by biting insects (Piesman and Gates 
1996, Apperson el al. 2004, Ostfeld et al. 2004). 
They are also exposed to potential pathogens and 
foreign microbes (and parasites) in the food 
delivered to them by adults, the nest material 
surrounding them, and their nest mates (Kyle and 
Kyle 1993. Hahn et al. 2000, Lochmiller and 
Deerenberg 2000). Innate immune function may 
be especially important to altricial nestlings 
because: (1) their relatively short incubation 
periods may result in poorly developed immune 
systems at hatching (Ricklefs 1992), and (2) their 
lack of mobility may resull in greater exposure to 
parasites (Ardia and Schat 2008). Altricial 
nestlings also have strong selection pressure to 
grow rapidly to fledge as soon as possible and 
leave the nest to avoid predation (Skutch 1976, 
O’Connor 1984). This suggests the rate of 
maturation of immune defenses reflects an 
evolutionary trade-off with physical growth and 
maturity required to fledge (Ardia and Schat 2008, 
Ardia et al. 2011, van der Most et al. 2011). 
Assessment of maturation of immune function 
in wild birds has been most frequently made using 
a single measurement, but we monitored immune 
development by assaying immunocompetence 
throughout the nesding period (Palacios et al. 
2009). We took samples at different points in the 
nestling period and measured one component of 
the innate immune response, i.e., the in vitro 
ability of whole blood to kill Escherichia coli, in 
altricial nestling Tree Swallows (Tachycineta 
bicolor), and compared it to adult innate immune 
function. We predicted the in vitro microbicidal 
779 
