Male Savannah Sparrows Provide Less Parental Care with
Increasing Paternity Loss
Noah G. Perlut, Lindsay M. Kelly, Nathan J. Zalik, and Allan M. Strong
Northeastern Naturalist, Volume 19, Issue 2 (2012): 235–344
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2012 NORTHEASTERN NATURALIST 19(2):335–344
Male Savannah Sparrows Provide Less Parental Care with
Increasing Paternity Loss
Noah G. Perlut1,*, Lindsay M. Kelly1, Nathan J. Zalik2, and Allan M. Strong2
Abstract - Male parental care can significantly affect fledging success and, therefore, is
a strong target of both natural and sexual selection. However, for songbird species that
exhibit extra-pair paternity, males may reduce parental care based on how much paternity
they have lost in a brood. We studied Passerculus sandwichensis (Savannah Sparrow)
male parental care relative to the proportion of extra-pair young in the nest, to see if males
adjusted care in response to increasing loss of paternity. Males brought less food (mass)
with increasing rates of extra-pair paternity, although male provisioning did not influence
fledging success. These results contrast with a previously published study of an island
population of this species, where males provided more parental care with increased loss
of paternity. We hypothesize that high rates of annual survival in this mainland population,
where males have a greater potential for reproduction in future years, may explain
this difference in behavior.
Introduction
Male parental care can significantly affect fledging success and may include
activities such as nest construction, incubation, nest and territory defense, and
offspring care. However, there is a conflict between the sexes with respect to the
extent of parental care and overall fitness; each sex would like the other to do
most of the work (Houston et al. 2005) because parental care can be costly in
terms of survival (Williams 1966). Male parental care may be especially costly
if it is provided for unrelated young (Trivers 1972). As a result of this conflict,
male parental care is a target of sexual and natural selection (Trivers 1972). Both
direct and indirect benefits of male parental care influence the strength of sexual
selection, particularly in species with high levels of extra-pair paternity (EPP)
(Møller and Thornhill 1998).
The responses of males to paternity loss may vary with social or environmental
contexts (Westneat and Sherman 1993, Whittingham and Lifjeld 1995,
Whittingham et al. 1992). Studies to date have provided mixed results concerning
the effect of lost paternity on male parental care, with increasing EPP
rates resulting in a reduction in male parental care in some species (Briskie et
al. 1998, Hoi-Leitner et al. 1999, Møller 2000, Mulder et al. 1994, Seki et al.
2007, Wagner et al. 1996), no effect on parental care in other species (Garcia-
Vigón et al. 2009, Peterson et al. 2001, Westneat et al. 1995, Whittingham and
Lifjeld 1995), and both increased and decreased provisioning rates depending
1University of New England, Department of Environmental Studies, 11 Hills Beach
Road, Biddeford, ME 04005. 2The Rubenstein School of Environment and Natural
Resources, University of Vermont, Burlington, VT 05405. *Corresponding author -
nperlut@une.edu.
336 Northeastern Naturalist Vol. 19, No. 2
on mating status in still other species (Whittingham and Dunn 1998). Males
may also provision nestlings at higher rates when they lose paternity in an
attempt to increase their paternity in subsequent broods (Burke et al. 1989,
Dixon et al. 1994, Freeman-Gallant 1997). Further, males may provision more
if their care influences overall fledging success, thereby increasing their overall
fitness (assuming some level of paternity in the brood). Increased male care
can give females the ability to increase fitness through investing more energy
into the nest and re-nesting sooner (Eliassen and Kokko 2008). Alternatively,
although providing parental care can increase their fitness, males may also
increase fitness by investing greater energy in mating with additional females
and focusing on self-maintenance (Arnold and Owens 2002, Cezilly and Nager
1995, Mauck et al. 1999).
To date, there appears to be no consistent pattern explaining how male birds
respond to cuckoldry. This lack of consistency suggests that ecological conditions
(e.g., breeding synchrony, nest density, and survival rate) may influence
male parental effort (reviewed in Griffith et al. 2002). However, to our knowledge,
Emberiza schoeniclus L. (Reed Bunting) is the only species that has been
studied (with respect to male parental care response to cuckoldry) in multiple
habitats across its geographical range. In response to paternity loss, male Reed
Buntings can adjust parental care (incubation and nestling provisioning) in subsequent
broods (Dixon et al. 1994), but are also known to not adjust parental care
(Bouwman et al. 2005).
Passerculus sandwichensis Gmelin (Savannah Sparrow) is an obligate grassland
songbird that breeds in diverse grassland habitats across northern North
America and show strong behavioral plasticity across their range (Wheelwright
and Rising 2008). This multi-brooded species exhibits biparental care, with variable
male feeding rates (Freeman-Gallant 1997, Wheelwright et al. 1992, Zalik
and Strong 2008), and has a mixed mating strategy (monogamy and polygyny)
that includes high rates of EPP (Freeman-Gallant 1998, Perlut et al. 2008a). On
Kent Island, NB, Canada, male Savannah Sparrows provided more parental care
with increased loss of paternity (Freeman-Gallant 1997). However, the ecology
and evolutionary processes of this island population likely differ from mainland
populations (e.g., vegetation composition, land-use history, weather, and
breeding density), particularly with populations breeding in agricultural habitats
(Perlut et al. 2008a).
Given the potential for regional differences in behavior and the paucity of
studies exploring EPP and male provisioning behavior across ecological boundaries,
we examined how provisioning rates of male Savannah Sparrows varied
in response to paternity loss. We explored this behavior in a mainland population
breeding in agricultural fields. Due to hay-harvest, this Savannah Sparrow
population is under strong ecological and evolutionary pressures. Because this
population shows high annual survival rates (Perlut et al. 2008b), we hypothesized
that males would lower parental care with increasing rates of EPP, thus
providing more time to invest in self-maintenance for future breeding opportunities.
Survival rates may influence how males respond to paternity loss; when male
2012 N.G. Perlut, L.M. Kelly, N.J. Zalik, and A.M. Strong 337
annual survival is greater than 70%, as in our study population, they should be
less tolerant of paternity loss (Mauck et al. 1999).
Methods
Savannah Sparrows are ground-nesting, grassland obligate songbirds with a
breeding distribution extending from the Atlantic to the Pacific oceans (Wheelwright
and Rising 2008). In 2004 and 2005, we studied Savannah Sparrows
breeding in two hayfields (17.6–18.5 ha) in Vermont’s Champlain Valley, which includes
146,000 ha of managed grassland (NASS 2009). One hayfield was mowed in
late May or early June and again in mid-July, and the second field was mowed in early
August. The two fields were 1.5 km apart, and no breeding adults moved between
fields within or between years. To minimize any potential influence of mowing, we
focused our study on first broods (before fields were mowed).
Beginning in mid-May of each year, we located nests through behavioral
observations. If not already banded, sparrows were captured with mist nets and
uniquely banded with 3 color bands and one US Geological Survey band. We
also took a small (20–60 μL) sample of blood; for birds that were banded previous
to this study, we used stored blood from the original capture. Because only
females incubate, female association was identified by flushing incubating birds
off nests. Male association was identified by provisioning and territory defense
behavior (Wheelwright and Rising 2008) as well as analysis of video recordings
(see below). We visited nests every one to two days to assess their status until
either fledging or nest failure. We used multiple criteria to determine if young
fledged: if they were present in the nest between day 8–10 and not present at the
subsequent nest check, if feces were found in the empty nest, and/or if adults
were seen nearby carrying food. Blood samples were taken from all nestlings in
each brood on day 6–7. Blood was put in a solution following Seutin et al. (1991),
and stored in a freezer or placed on a Watman disc filter paper, allowed to dry,
stored in plastic zip-loc bags with silica desiccation beads, and kept in a freezer
until extraction.
We only videotaped nests where males were observed to actively defend their
territory and mate guard (to be assured that the male had not deserted the nest).
We videotaped nests when nestlings were 4 to 7 days old (the peak of food demand
for this species; Bedard and Meunier 1983, Freeman-Gallant 1998) using
either an 8-mm camcorder (Sony TRV-460 Digital8) mounted on a tripod (2004)
or a small, wide-angle lens (www.helmetcamera.com) placed 20 to 30 cm from
the nest (2005). The lens was connected by cable to the Sony camcorder placed
2 m from the nest and concealed by vegetation. Nests were recorded once for 1.5
hr in the morning, beginning between 0710 and 0936. We excluded the first 15
min of each tape to allow the birds to become acclimated to the camera’s presence.
One observer (N.J. Zalik) quantified the number of feeding trips during
each recording session and converted this data to an hourly rate. We identified
males and females by the combination of their colored leg bands. Prey size was
338 Northeastern Naturalist Vol. 19, No. 2
estimated by one person (N.J. Zalik) comparing the size of the prey with the exposed
portion of the adult’s bill (11.2 mm) as a reference and pooling prey into
categories in multiples of 11.2 mm. The mass of each prey item was estimated
using length-mass regression equations developed from invertebrates collected
at our field sites based on mid-points of each length category (i.e., 5.6 mm, 16.8
mm, 28 mm; Zalik and Strong 2008).
All molecular and paternity analysis followed Perlut et al. (2008a). We used
four hypervariable microsatellite loci (Table 1) to assess parentage: Psa12,
Passerculus sandwichensis (Freeman-Gallant et al. 2005); Escu6, Emberiza
schoeniclus (Hanotte et al. 1994); Mme1 and Mme8, Melospiza melodia Wilson
(Song Sparrow; Jeffery et al. 2001). We assigned paternity by hand. All offspring
matched their mothers and fathers at all four loci. Extra-pair males were identifi
ed only if they matched all non-maternal alleles at all four loci. Our population
showed high allele diversity (Table 1), providing confidence in paternity assignment,
with a 0.91547 probability of exclusion.
With SAS 9.2 (SAS Institute, Cary, NC), we used analysis of variance to test
the relationship between feeding behavior and the percentage of extra-pair young
in broods. Three variables described parental care by males: mass of food (mg)
delivered per nestling per hour, average load size (average mass of prey delivered
per visit), and number of feeding trips per hour. We controlled for the number of
nestlings in a brood by dividing the food mass, load size, or number of trips by
the number of nestlings. These models included day (age of nestling) and year as
a fixed effect to control for differences in parental care relative to nestling age.
We used analysis of variance to test the relationship between male parental care
and fledging success (defined as the number of successfully fledged offspring).
All analyses are from first broods only (except one analysis comparing EPP in a
males’ first and second brood with the same female). We controlled for multiple
comparisons of individual females because two females were sampled in both
years. Values are presented as means ± 1 SD. We used Cook’s distance to test if
outliers had an unusually strong effect on our sample.
Results
We obtained video and paternity data for 13 nests; nine nests (69%) had at
least one extra-pair young, and 47% of all offspring were extra-pair. The average
Table 1. Number of alleles (Na), observed heterozygosity (Ho), expected heterozygosity (He) for
148 breeding adults (53 female, 95 male) Savannah Sparrows in the Champlain Valley, VT. Escu6
= Emberiza schoeniclus (Hanotte et al. 1994); Mme1 and Mme8 = Melospiza melodia (Jeffery et
al. 2001); Psa12 = Passerculus sandwichensis (Freeman-Gallant et al. 2005).
Locus Na Ho He
Escu6 19 0.865 0.923
Mme1 38 0.748 0.943
Mme8 22 0.859 0.909
Psa12 10 0.709 0.754
2012 N.G. Perlut, L.M. Kelly, N.J. Zalik, and A.M. Strong 339
number of extra-pair young per nest was 1.5 ± 1.3. Brood size (3.2 ± 0.73; range
= 2–5) and nestling age at time of videotaping (5.8 ± 0.9 days; range = 4–7 days)
were generally consistent across the sample.
Males brought less food (mass) per hour with increasing numbers of extrapair
young in their nests (F2,12 = 6.1, P = 0.02; Fig. 1, see Table 2 for mass rate).
Females also brought less food (mass) with increasing rates of EPP (F2,12 = 3.86,
P = 0.05). Additionally, male average load size was lower with increasing rates of
EPP (F2,12= 6.6, P = 0.01; Fig. 1). Female load size was also lower with increasing
rates of EPP (F2,12= 5.29, P = 0.02). However, male feeding rates did not change
with EPP (range = 0–6 trips per hr; F2,12 = 1.8, P = 0.10). EPP did not affect how
often females visited nests (F2,12 = 3.1, P = 0.08).
Table 2. Load size (mg), feeding rate (trips per hour), and prey mass delivery rate (mg) for 13 Savannah
Sparrow nests in the Champlain Valley of Vermont (mean ± SD). EPP represents nests that
had at least one extra-pair young. No EPP represents nests that had no extra-pair young.
Overall EPP No EPP
Load size
Male 21.43 ± 32.99 8.75 ± 10.70 49.94 ± 49.81
Female 27.93 ± 23.01 21.40 ± 13.05 42.62 ± 35.33
Feeding rate
Male 0.63 ± 0.74 0.60 ± 0.85 0.71 ± 0.53
Female 1.41 ± 1.02 1.39 ± 0.99 1.48 ± 1.23
Mass rate
Male 21.48 ± 28.96 11.13 ± 16.19 44.77 ± 40.13
Female 54.54 ± 73.73 36.58 ± 27.61 94.97 ± 128.70
Figure 1. Male Savannah Sparrows in the Champlain Valley, VT, brought less food,
both in terms of the overall load and food mass per nestling, to broods where they lost
more paternity (n = 13 nests). Only 11 data points are shown here because two nests had
equivalent values. Cook’s distance analysis showed that no single nest caused unusual
skew to the data.
340 Northeastern Naturalist Vol. 19, No. 2
Broods with more extra-pair young tended to fledge more young than broods
with fewer extra-pair young (F2,12 = 6.7, P = 0.03). Male provisioning (mass) did
not affect fledging rates (F2,12= 0.02, P = 0.89). Cook’s distance analysis showed
that no single nest caused unusual skew to the data.
Discussion
We found that male Savannah Sparrows delivered less prey mass with increasing
rates of paternity loss. Although males that lost more paternity fed less, this
lower parental care apparently had little effect on fledging success; nests with
more EPP fledged more young. These results contrast to those of an island population
of this species, where males provided more parental care with increasing
rates of extra-pair paternity (Freeman-Gallant 1997). In both populations, male
care may have had little influence on fledging success. While we did find a signifi
cant effect of mass and load size, as has been observed with other studies,
male feeding rates were not affected by EPP.
Our results suggest that pressures affecting parental care may vary regionally.
Although mainland vs. island is the most obvious difference between our
study site and Kent Island, abiotic factors, ecological conditions (synchrony,
density, food, land use), and the sampling period and study design may also
influence differences in results. However, differences between the populations’
demographic rates may influence the observed difference in behavior and should
be underscored. On Kent Island, male return rates are highly variable (37–73%;
Wheelwright et al. 1992), and poor-quality males (low reproductive success) have
low survival rates (C.R. Freeman-Gallant, Skidmore College, Saratoga Springs,
NY, pers. comm.); a male may therefore make the best of a bad situation by caring
for his low paternity brood rather than investing in further mating efforts. There
is support for survival rates as being strongly influential on how males respond to
paternity loss; when male annual survival is greater than 70%, they should be less
tolerant of paternity loss (Mauck et al. 1999). In the Vermont population, male
apparent survival is extremely high in hayfields (73–85%; Perlut et al. 2008b). In
deciding to lessen their nestling-provisioning efforts, males may choose to either
a) prospect for EPP opportunities with secondary females, or b) invest in selfmaintenance
to increase survival for future mating opportunities. If males indeed
decided to invest in their own survival rather than nestling care, then this case is
a rare example for migratory passerines that do not establish lasting pair bonds.
Moreover, high survival rates can explain EPP behavior for seabirds (Baiao and
Parker 2009, Lifjeld et al. 2005) and some passerines (Taylor et al. 2008), but
these species typically have low EPP rates and long-term pair bonds. Therefore,
comparisons with species that have high EPP rates and seasonal pair bonds may
not be informative.
Others have found that reducing parental care did not affect male survival
(Bouwman et al. 2005). Therefore, it is important to consider other factors
that may have also influenced our results. For example, because males showed
2012 N.G. Perlut, L.M. Kelly, N.J. Zalik, and A.M. Strong 341
differences in load and not feeding rates, our results may also be affected by
prey availability or foraging efficiency. Although there is little resource variation
within a given field (Zalik and Strong 2008), territory quality could have
also affected our findings. Additionally, both within this (Perlut et al. 2008a)
and the Kent Island population (Wheelwright and Rising 2008), the social mating
status of a male (monogamous, polygynous) affects the amount of paternity
loss (however, Dixon et al. [1994] found no effect of mating status). Finally,
males who are cuckolded more frequently may simply be lower quality birds
with lower survival and less parental care. Future study, including a larger sample,
should explore these factors.
That higher male parental care (via mass) did not lead to increased fledging
rates may have implications for the evolution of mate choice by females. This
finding is important because Lotem et al. (1999) found that female choice
may drive male behavior by rewarding males with increased paternity for preferred
behaviors like parental care. Thus in our system, females are unlikely
to evaluate and reward males (by increasing paternity in subsequent broods)
who bring more food mass because this aspect of male parental care does not
increase female fitness. On Kent Island, males base their feeding behavior
on the potential to increase or gain paternity in subsequent broods (Freeman-
Gallant 1997). Our sample was insufficient to test this hypothesis robustly;
however, we found no correlation between a male’s paternity in his first brood
and his paternity in his second brood. Due to the effects of hay harvest on one
of our study sites, we could not evaluate whether male parental care provides
advantages to females for renesting or second broods. Overall, our findings
suggest that in this population male feeding rates are not targets of selection
for Savannah Sparrows, and that the ways in which males may respond to
lost paternity may vary across a species’ range due to variation in life-history
traits and ecological conditions. Because our sample size was relatively small
and collected over a two-year period, further study is needed to understand
how geographic and habitat variation affects the relationship between paternal
care and extra-pair paternity; we encourage others to explore these behaviors
across a species’ distribution.
Acknowledgments
The project was supported by the Initiative for Future Agricultural and Food
Systems and the National Research Initiative of the US Department of Agriculture–
Cooperative State Research, Education, and Extension Service (grant
numbers 2001-52103-11351 and 03-35101-13817, respectively). Additional
funding was provided by the Natural Resource Conservation Service’s Wildlife
Habitat Management Institute. C. Freeman-Gallant and N. Wheelwright provided
helpful discussion and reviews of early drafts. We thank Shelburne Farms for
generous access to their land. Thanks to each summer’s army of research assistants’
excellent work.
342 Northeastern Naturalist Vol. 19, No. 2
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