Territorial behavior of the migratory Lined Seedeater during the breeding season

Abstract

Most bird species will defend a territory during the breeding period to assure the availability of resources for their reproductive success. Migratory birds abdicate their territory ownership during the non-breeding period, posing a challenge for the following breeding season. Here we investigated the territorial behavior of male Lined Seedeaters Sporophila lineola, an intra-tropical migrant, during the breeding season (December–May) 2018/2019 in south-eastern Brazil. The Lined Seedeater is a sexually color-dimorphic species that inhabits open areas and feeds on seeds. We followed 18 color-banded individuals, during the period in which they had an active nest. For each individual, we recorded the locations in which they exhibited any potential territorial behavior, with the aid of a handheld GPS. We then estimated the size and shape of the territories using a Kernel Density Estimator. The breeding territories had on average 0.59 ± 0.24 ha, ranging from 0.21 to 0.91 ha in area. Males exhibited agonistic behavior whenever another male intrudes on their territories, especially if in the vicinity of their nests. Our observations indicate that male Lined Seedeaters defend small territories of exclusive use during the breeding season, but forage over a wider home range shared with other conspecifics. Therefore, Lined Seedeaters and other members of Sporophila seem to exhibit home ranges that are much larger than their breeding territories. Empirical studies are needed to understand the influence of territory size and quality on reproductive fitness.

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https://doi.org/10.1007/s43388-021-00065-y
ORIGINAL ARTICLE
Territorial behavior ofthemigratory Lined Seedeater
duringthebreeding season
Gustavode MeloMartins1,2 · FilipeC.R.Cunha3 · LeonardoEstevesLopes1
Received: 26 March 2021 / Revised: 19 August 2021 / Accepted: 20 August 2021
© Sociedade Brasileira de Ornitologia 2021
Abstract
Most bird species will defend a territory during the breeding period to assure the availability of resources for their reproduc-
tive success. Migratory birds abdicate their territory ownership during the non-breeding period, posing a challenge for the
following breeding season. Here we investigated the territorial behavior of male Lined Seedeaters Sporophila lineola, an
intra-tropical migrant, during the breeding season (December–May) 2018/2019 in south-eastern Brazil. The Lined Seedeater
is a sexually color-dimorphic species that inhabits open areas and feeds on seeds. We followed 18 color-banded individuals,
during the period in which they had an active nest. For each individual, we recorded the locations in which they exhibited
any potential territorial behavior, with the aid of a handheld GPS. We then estimated the size and shape of the territories
using a Kernel Density Estimator. The breeding territories had on average 0.59 ± 0.24ha, ranging from 0.21 to 0.91ha in
area. Males exhibited agonistic behavior whenever another male intrudes on their territories, especially if in the vicinity of
their nests. Our observations indicate that male Lined Seedeaters defend small territories of exclusive use during the breeding
season, but forage over a wider home range shared with other conspecifics. Therefore, Lined Seedeaters and other members
of Sporophila seem to exhibit home ranges that are much larger than their breeding territories. Empirical studies are needed
to understand the influence of territory size and quality on reproductive fitness.
Keywords Birds· Breeding biology· Neotropics· Kernel Density Estimator
Introduction
Territorial behavior is one of the most elementary aspects
of a species’ natural history, with most bird species defend-
ing some type of territory during at least part of their lives
(Alcock 2016). The comparatively few studies on territorial-
ity ever conducted in tropical zones were mostly performed
with year-round resident species (Greenberg and Gradwohl
1997; Lopes and Marini 2006; Duca and Marini 2014), and
almost nothing is known about the territorial behavior of
migratory species, especially the intra-tropical migrants.
Here, we investigated the territorial behavior and estimated
the breeding territory size of the Lined Seedeater Sporophila
lineola (Thraupidae).
The Lined Seedeater is a small granivorous songbird
with a diagnostic sexually color-dimorphic plumage with
adult males exhibiting a distinctive black-and-white plumage
that strongly contrasts with the dull brownish plumage of
females; young males exhibit a female-like brownish plum-
age (Ridgely and Tudor 2009). The species is widespread
throughout much of South America, where it inhabits a vari-
ety of open habitats (Ridgely and Tudor 2009). This is an
intra-tropical migratory species, with the studied population
breeding in south-eastern Brazil from December to April
(Oliveira etal. 2010; Ferreira and Lopes 2017), then migrat-
ing to the northern part of South America, where it winters
(Silva 1995). However, to this day little is known about its
migratory habits and pathways.
Communicated by Cristiano Azevedo.
* Gustavo de Melo Martins
gustavo95melo@gmail.com
1 Laboratório de Biologia Animal, IBF, Universidade Federal
de Viçosa – Campus Florestal, Florestal, MinasGerais,
Brazil
2 Present Address: Programa de Pós-Graduação em Ecologia,
Instituto Nacional de Pesquisas da Amazônia, Manaus,
Amazonas, Brazil
3 Behavioural Ecology Group, Wageningen University &
Research, Wageningen, TheNetherlands
/ Published online: 3 September 2021
Ornithology Research (2021) 29:133–139

1 3
A territory is of crucial importance for the reproductive
fitness of an individual since it can comprise the necessary
resources to successfully raise offspring (Verner 1977;
Lobato etal. 2010). Migratory birds face a particular
challenge since they abdicate of territory ownership between
breeding seasons; therefore, it is assumed that as soon as
the males are refueled from their migratory journey, they
would then start to claim and/or re-claim their territories
(Greenberg 1986). In Lined Seedeaters, the territory plays
an important role in mating. Females build the nest alone
and assume the main role over incubation and feeding
(Ferreira and Lopes 2017); thus, it is assumed that territory
is a valuable resource to which males would then compete
over it. Little is known about territorial behavior of Lined
Seedeaters; thus, in this study, we analyzed territory size and
investigate territorial behaviors displayed by males. In this
study, we cover a gap in the knowledge of the natural history
of the species shedding new light for future empirical studies
on the function and mechanism of territorial behavior and
fitness interplay.
Methods
We conducted our field observations in the Campus Flor-
estal of the Universidade Federal de Viçosa, municipality of
Florestal, state of Minas Gerais, south-eastern Brazil. The
study area lies in the transition zone between the Cerrado
savannas and the Atlantic Forest biogeographic provinces
(IBGE 2004). Climate in Florestal is subtropical with a dry,
mild winter, and a humid, hot summer (Lopes and Marçal
2016). The Campus Florestal is about 1500ha, covered by
fragments of secondary semideciduous forests and by sev-
eral types of man-made open habitats, including extensive
pastures of African grasses, cultivated areas, extensive gar-
dens around the main buildings, and several small ponds
(Ferreira and Lopes 2017).
This study is part of the Lined Seedeater Project, which
monitors a breeding population of the species since 2014.
After the arrival of the first migratory birds in the study area
in the first week of November 2018, we began to search for
territorial males and mist-netting those males that have not
been banded during previous breeding seasons. Unmarked
males were then banded with a numbered metallic band and
a unique combination of three colored plastic bands, which
allowed individual identification with the aid of binoculars
(Fig.1). Our fieldwork extended until May 2019, when birds
migrated to their wintering grounds, marking the end of the
breeding season.
We defined breeding territories as the defended area around
the nest location (Welty and Baptista 1988; Maher and Lott
1995). Once we discovered a nest during the construction
stage or early incubation, we followed the males collecting
the data points on their geographical locations of the territo-
rial male until nest failure or success. With a handheld GPS
device (Garmin™ eTrex 30 × , 3–5m precision), we marked
the locations where the male was observed singing, fighting
other males, and/or copulating. We marked a new location for
every displacement, but only after the male spontaneously left
the perch, to interfere as less as possible on its behavior. We
sampled each territory for the duration of a single reproductive
event, during at least 6 different days. We assume this is the
minimum amount necessary for sampling the territory, so as
not to bias the results due to the constant human presence. This
decision was made based on our experience obtained from
monitoring previous seasons with the species.
To estimate territory size, we used the Kernel Density
Estimator, implemented in the ‘rhr’ package (Signer and
Balkenhol 2015) in R software (R Core Team 2016). The
Kernel Density Estimation was calculated for a contour
value of 95% and using the reference bandwidth, since this
method is appropriate when the locations are arranged as a
single tight cluster (Signer and Balkenhol 2015). We also
investigated site fidelity using the mean square distance
from the center of activity and verified if the territories
reached an asymptote (e.g., Laver and Kelly 2010; Signer
and Balkenhol 2015). Territories with less than 30 locations
were discarded (e.g., Seaman etal. 1999). The software
QGIS and Google Earth Satellite images were used to
prepare the map depicting the home ranges.
Results
Overall, we assessed and monitored 19 breeding territo-
ries belonging to 18 males. For one male (Male number
8, Fig.2), we estimated the size of the two territories this
Fig. 1 Male of Lined Seedeater Sporophila lineola color-banded in
the study area, southeastern Brazil
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individual held during the breeding season. This male paired
with two distinct females, the first paired female was not
observed in the study area after the first nesting attempt. Six
males were captured between November and March 2019.
The other 12 males were banded during previous breeding
seasons.
The first Lined Seedeaters arrived in the study area on
06 November 2018, when we observed five males in the
adult black-and-white plumage foraging. Even though these
males eventually sang, we observed no sign of aggressive-
ness between them. On 11 November, we observed four
other males foraging side by side, but no aggressive behavior
was recorded during the 5days these birds shared a grass
patch, in which Male 4 established his territory for the sea-
son (Fig.2).
The number of individuals recorded in the study area
increased over the days with the arrival of new males. The
first female, however, was only recorded in the study area
on 17 November, 11days after the arrival of the first males.
During the first 2weeks, individuals shared feeding areas,
and even though they eventually sang, they were mostly tol-
erant with one another. On 28 November, the first two ter-
ritories were established, as evidenced by the observation of
the first territorial disputes and an increase in song output.
For example, Male 4 chased and evicted another male that
invaded its territory on three occasions on the same day, on
01 December. Male 7, who has previously been seen twice
sharing a feeding area with other conspecifics, chased away a
brownish male that sang within its territory on 02 December.
Only one of males monitored, Male 12 (Fig.2), was in
the brownish plumage, while all other males were in the
adult plumage. We obtained 1260 geographical locations,
in an average of 66.3 ± 19.2 locations per territory, ranging
from 39 to 99 locations. Males from all territories studied
exhibited site fidelity, but four of the 19 territories monitored
did not reach an asymptote (Supplementary Material S1).
Breeding territories were on average 0.59 ± 0.24ha in area,
ranging from 0.21 to 0.91ha (Table1).
At the present study, 10 out of the 18 males occupied
roughly the same territories where they have bred during
the previous season, as evidenced by the location of their
nests monitored 1year before (Table1). However, one of
these individuals, Male 8, had another reproductive attempt
in a distinct territory. After breeding successfully during the
2017–2018 breeding season, this individual returned to the
same site in the 2018–2019 breeding season, but after suc-
ceeding in a first attempt, this same individual moved about
300m southwestward, where it established a distinct terri-
tory (see Fig.2b). Two other males banded during previous
breeding seasons changed the location of their territories,
with Male 11 moving about 850m (in relation to the border
of his current territory) from the place where his nest was
monitored the year before. Male 4 moved about 300m from
the place where it was captured during the previous breed-
ing season. The remaining six males were banded during
this study, but three of which established territories in areas
that were occupied by other banded males whose nests were
monitored during the previous breeding seasons. Therefore,
Males 12, 14, and 16 occupied their territories for the first
time.
Even though in Lined Seedeaters nest construction and
incubation are performed exclusively by females, males
usually stay close to females during nest construction. In
four occasions, we observed the male chasing the female
briefly after she added new material on the nest, returning
Fig. 2 Breeding territory size of eighteen males of Lined Seedeaters
Sporophila lineola monitored in southeastern Brazil. Black areas are
territories held by males in relation to the previous breeding season;
red areas represent males that have changed the location of their ter-
ritories between seasons or during a same season; yellow areas repre-
sent males color-banded in the 2018–2019 season and for which we
have no previous information. Note that the Male 8 held two distinct
territories (8a and 8b) estimated during two distinct nesting attempts.
Black triangles indicate the approximate location of the center of the
territory of other territorial males that have not been sampled during
this study. Black stars indicate shared feeding zones where at least
one banded male was observed side by side with other individuals
during a nesting attempt
135Ornithology Research (2021) 29:133–139

1 3
afterward to a singing perch close to the nest. Males are the
main responsible for nest guarding and territorial defense,
singing on high perches close to the nest, usually facing it,
for most of the day, even under apparently adverse weather
conditions (e.g., when drizzling or in the hottest hours of the
day). Only on rare occasions, we observed females engaged
in agonistic interactions with other Lined Seedeaters, includ-
ing attacks to other males (n = 3) and to a brown individual
of undermined sex that has approached on the nests.
Males did not tolerate the invasion of their territories
by other males, especially if close to their nests. When this
occurred, the resident male often evicted the intruder. Dur-
ing this study, we observed 17 agonistic encounters between
males, most of them during the nest construction period
(n = 9). Territorial disputes were frequent throughout the
breeding season, eventually leading to adjustments in the
territory borders or even to the replacement of the territory
owned by another male. For example, the territory of Male
5 was delimited at the beginning of the breeding seasons,
before the arrival of the two other males indicated in Fig.2a
and whose territories have not been sampled. Later in the
season, these three males stayed in the same area, occupying
very small territories with apparently no or only negligible
overlap between them.
The purported overlap between the territories of Males 3
and 4, as well as between Males 9 and 10 (Fig.2) did not occur
temporally, with each male occupying the area of overlap only
during a distinct period of the breeding season. Males 17 and
18 were observed disputing a territory on 18 November, dur-
ing the early breeding season. We observed at least four ago-
nistic encounters between them, until Male 17 eventually won
the territory dispute, with Male 18 being forced to occupy
an adjacent territory. Male 5 took the territory of another
unbanded male that occupied the same area at the beginning
of the breeding season.
Males and females of the Lined Seedeater frequently feed
in grassland patches out of their territories. These feeding
areas were used by several individuals of the species, some-
times simultaneously (e.g., two black-and-white males and
two brown unsexed birds were observed foraging side by
side in grassland between Males 16 and 17; Fig.2c). Male
5, for example, has established its territory in a parking lot
with no food sources available in there. This male usually
foraged in a grassland patch about 150m from the borders
of its territory, in a feeding area that was also used by his
neighbor males and other conspecifics. These feeding areas
were also shared with other granivorous species, such as the
Yellow-bellied Seedeater Sporophila nigricollis, the Saffron
Finch Sicalis flaveola, and the Blue-black Grassquit Volat-
inia jacarina, with intra or interspecific agonistic encounters
seldom occurring.
Table 1 Breeding territory
size of 18 males of Lined
Seedeaters Sporophila lineola.
Estimates were obtained with
the Kernel Density Estimator
using the reference bandwidth
and a 95% contour value. The
table indicates if the birds
exhibited site fidelity and if
their territories reached an
asymptote, as well as whether
the individuals maintained their
territories from the previous
season, except those that were
captured during the present
study (–)
* Male 8 had two distinct territories estimated during distinct nesting attempts
Male Number of points Area (ha) Site fidelity Asymptote Kept territory
1 50 0.25 Yes Yes Yes
2 45 0.21 Yes Yes Yes
3 50 0.80 Yes Yes Yes
4 98 0.72 Yes Yes No
5 63 0.84 Yes No –
6 83 0.41 Yes Yes Yes
7 59 0.91 Yes No Yes
8a 85 0.88 Yes Yes Yes
8b 71 0.81 Yes No No*
9 39 0.20 Yes Yes Yes
10 45 0.48 Yes Yes Yes
11 56 0.60 Yes Yes No
12 68 0.49 Yes Yes –
13 98 0.44 Yes Yes –
14 52 0.34 Yes Yes –
15 99 0.31 Yes Yes Yes
16 54 0.73 Yes No –
17 64 0.55 Yes Yes Yes
18 81 0.85 Yes Yes –
Mean ± SD 66.3 ± 19.2 0.59 ± 0.24
136 Ornithology Research (2021) 29:133–139

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Discussion
As soon as Lined Seedeaters arrive on their breeding
grounds, males exhibit a tolerant social behavior toward
other males, similarly to what is observed on their winter-
ing grounds in the savannas of Surinam and Venezuela,
where small flocks of the species are commonly seen, with
several males foraging side by side (Haverschmidt 1968;
Thomas 1979). This behavior persisted in the study area
for about 2weeks, while males foraged in a small corn
plantation with some invasive African grasses and other
seed-bearing weeds. This plantation, which was located at
the central upper portion of Fig.2c, was subsequently not
used for breeding by any male.
Territories of Lined Seedeaters and other congeneric
species are defended by the males (Areta etal. 2013; Franz
and Fontana 2013; Ferreira and Lopes 2017; Rosoni etal.
2019), which usually sing on high and exposed perches
close to the nest (Rovedder and Fontana 2012; Franz and
Fontana 2013; Repenning and Fontana 2016). Concerning
territory size, our findings suggest that territories of Lined
Seedeater are smaller than those of some other species of
the genus, such as the Rusty-collared Seedeater (S. colla-
ris; 3.22ha, Rosoni etal. 2019) and the Tropeiro Seedeater
(S. beltoni; 1.60ha, Repenning 2012), but slightly larger
than that found for the Black-bellied Seedeater (S. mela-
nogaster; 0.27ha, Rovedder 2011).
The breeding territories of Lined Seedeaters are very
small, with most territories studied covering a radius of
only a few dozen meters around the nest. There was, how-
ever, great variation in territory size between the eighteen
males studied, with the largest territory (0.91ha) exhibit-
ing an area four and a half times larger than the smallest
territory (0.20ha) studied. There are several explanations
for such large variation in territory size, including differ-
ences in the previous breeding experience of males, dif-
ferential abundance of resources, or even the presence of
physical barriers (e.g., high buildings and ponds, Fig.2)
that can impose limits to the size and shape of territories
(Hinde 1956; Powell 2000; Barg etal. 2005).
Our observations also suggest that territorial defense
is probably not related to the defense of food resources
in Lined Seedeaters, since birds frequently feed out of
their territories (i.e., the home range, even though not
measured, are much larger than their territories). Given
that most of the agonistic encounters recorded during this
study occurred during the nest construction period (i.e.,
when females are supposed to be fertile), we suggest that
territorial defense in Lined Seedeaters may have an impor-
tant role in avoiding extra-pair paternity (Rovedder and
Fontana 2012). On the few occasions that we observed an
intruder male perched in the same tree where the nest of
the territory owner was located, the intruder was chased
by the resident pair, who evicted it. This behavior was
observed five times during nest building and three times
when the nest contained nestlings. Similar behavior was
reported for the Double-collared Seedeater Sporophila
caerulescens (Francisco 2006).
After egg laying and the onset of incubation, males of
the Lined Seedeater apparently expanded their home ranges,
exploring feeding areas more distant from their nests and ter-
ritories. The use of feeding areas far apart from the breeding
territory has also been reported for other species of Sporoph-
ila, such as the Rusty-collared Seedeater (Rosoni etal. 2019)
and the Black-bellied Seedeater (Rovedder 2011), which
have been recorded using feeding areas as far as 1.4km from
its breeding territory. Therefore, Lined Seedeaters and other
members of Sporophila seem to exhibit home ranges that are
much larger than their breeding territories.
The defense of year-round multi-purpose territories
is a common strategy among resident tropical birds, with
migratory species usually defending territories only during
the breeding season (Stutchbury and Morton 2001). The
territorial behavior of Lined Seedeaters has already been
highlighted by Sick (1997) and Ferreira and Lopes (2017),
who reported frequent vocal disputes and agonistic encoun-
ters between males of the species. Agonistic interactions
between males consisted of single, isolated events (e.g.,
attempts of extra-pair copulations) or could last for days
(e.g., true territorial disputes), as observed in one of the ter-
ritories monitored, where a black-and-white plumaged bird
(Male 5) disputed its territory with an unbanded brownish
male during 3 consecutive days. Frequent disputes, espe-
cially at the beginning of the breeding season, have also been
reported for the Tropeiro Seedeater (Repenning 2012). The
Black-bellied Seedeater, on the other hand, did not present
a high frequency of territorial intrusions (Rovedder 2011).
The only brownish male we monitored was banded in its
breeding territory in the 2018–2019 breeding season. Lined
Seedeaters, as many other species of Sporophila, exhibit
delayed plumage maturation (Hawkins etal. 2012), with the
black-and-white adult plumage being acquired only during
the second cycle (Ferreira 2019). These young brownish
males were already known to successfully breed (Oliveira
etal. 2010; Ferreira and Lopes 2017), but this is the first
time its territorial behavior was studied. This brownish male
defended a 0.49-ha territory, which was slightly smaller
than the mean 0.59ha territory size recorded in this study,
but larger than the territory of eight black-and-white males
monitored in this study (Table1).
Our findings reported here represent an advance to our
understanding of the behavioral ecology of Lined Seedeat-
ers, raising some additional questions that deserve further
empirical investigation such as the traits that define the qual-
ity of a territory that is tangible with reproductive fitness.
137Ornithology Research (2021) 29:133–139

1 3
Given the migratory nature of Lined Seedeater, it is unclear
if migratory schedule influence territory quality, size, and/or
occupancy. The present work sheds new light on the natural
history of Lined Seedeater and opens new venues for the
study of long-standing evolutionary puzzles.
Supplementary Information The online version contains supplemen-
tary material available at https:// doi. org/ 10. 1007/ s43388- 021- 00065-y.
Acknowledgements Currently, G. M. M. is a scholarship holder
(132316/2020-0) from the Conselho Nacional de Desenvolvimento
Científico e Tecnológico (CNPq) and previously received a scholar-
ship from the same funding agency in the Programa Institucional de
Bolsas de Iniciação Científica. CNPq which also awarded a research
scholarship to L.E.L. (309660/2017-3). Wageningen University and
Research and the Netherlands Institute of Ecology funded part of this
study. Universidade Federal de Viçosa allowed us to conduct this study
in the area under their care. Permits for this project were granted by
Instituto Chico Mendes da Conservação da Biodiversidade (61078-
1) and Comissão de Ética no Uso de Animais–Universidade Federal
de Viçosa (03/2018). We thank the Lined Seedeater Project team for
their help during data collection, especially Aléxa Silva, Aléxia Gui-
marães, Ana Maria Medeiros, Bárbara Couto, Dalila Ferreira, Gabriela
Oliveira, Júlia Palhares, Lucas de Oliveira, Mayllin Lage, Melindy
Dirks, Robert Benjamins, Tessa van de Bemt, Vinícius Nicolau, and
Yvonne van de Weetering.
Funding Gustavo de Melo Martins is a scholarship holder
(132316/2020–0) from the Conselho Nacional de Desenvolvimento
Científico e Tecnológico (CNPq). When the field data was collected,
Gustavo was a scholarship holder for CNPq in the Programa Institu-
cional de Bolsas de Iniciação Científica from UFV (PIBIC–UFV).
Leonardo Esteves Lopes is also awarded a research scholarship from
CNPq (309660/2017–3). The Lined Seedeater Project is financed by
the Wageningen University and Research and the Netherlands Institute
of Ecology.
Availability of data and material The raw data with all localities are
available at a separate file (.xlsx).
Declarations
Ethics approval Permits for this project were granted by Instituto Chico
Mendes da Conservação da Biodiversidade (61078–1) and animal pro-
cedures were approved by the Comissão de Ética no Uso de Animais–
Universidade Federal de Viçosa (03/2018).
Consent to participate All the authors consent to participate in this
study.
Consent for publication All the authors consent to publish this study.
Conflict of interest The authors declare no competing interests.
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