Video recordings of Brown-headed Cowbirds (Molothrus ater) at the nests of grassland birds are of interest because relatively few such observations exist. We documented 7 events where cowbirds removed nest contents at 6 active nests and 1 empty nest. Among 6 attended nests, cowbirds arrived at the nest an average of 3.8 min (range 0.7–11.6 min) after the host species left. Cowbirds removed nest contents during the early morning (mean = 3.9 h after sunrise, SE = 0.3 h, n = 4) or late afternoon (mean = 13.1 h after sunrise, SE = 0.4 h, n = 3), taking an average of 0.7 min (range 0.4–1.1 min) to remove nest contents. Cowbirds sequentially moved nest contents away from the nest in 4 of the 7 events taking an average of 3 trips (range 2–4) to do so. Among 6 attended nests, cowbirds left the nest an average of 3.4 min (range 0.5–10.7 min) before the host species arrived back at the nest. Of the 6 active nests, cowbird damage of nest contents directly resulted in the failure of only 1 nest. Three nests went on to fledge the remaining host young, while 2 failed due to other causes. Our observations add to a growing number of video-recorded behaviors of brood parasites that can provide data for better testing hypotheses about nest destruction behavior.

Huevo de tordo Molothrus ater y destrucción de polluelos en nidos de aves de praderas del sudoeste de Wisconsin

Video grabaciones de tordo Molothrus ater en nidos de aves de praderas son de interés ya que existen relativamente pocas observaciones de este tipo. Documentamos 7 eventos donde los tordos removieron el contenido de nidos de 6 nidos activos y 1 nido vacío. Entre los 6 nidos ocupados, los tordos llegaron en promedio 3.8 min (rango 0.7–11.6 min) después de que la especie hospedera se fuera. Los tordos removieron los contenido de los nidos durante el inicio de la mañana (promedio = 3–9 h después del amanecer, SE = 0.3 h, n = 4) o al final de la tarde (promedio = 13.1 h después del atardecer, SE = 0.4 h, n = 3), tardando en promedio 0.7 min (rango 0.4–1.1 min) en remover el contenido de los nidos. Los tordos movieron secuencialmente el contenido de los nidos lejos de los nidos en 4 de los 7 eventos, lo que les tomó un promedio de 3 viajes (rango 2–4). Entre los 6 nidos ocupados, los tordos dejaron el nido en promedio 3.4 min (rango 0.5–10.7 min) antes de que la especie hospedera regresara al nido. De los 6 nidos activos, el daño del contenido del nido por los tordos resultó directamente en el fallo de anidación de sólo 1 nido. Tres nidos llegaron a emancipar el polluelo joven del hospedero, mientras 2 fallaron por otras causas. Nuestras observaciones suman al número creciente de comportamientos video grabados de parásitos de nidos que pueden brindar datos para probar hipótesis acerca del comportamiento de destrucción de nidos.

Palabras clave: archivos digitales, parásito de nido, praderas, remoción de huevo, remoción de polluelo, tasa de parasitismo, tordo Molothrus ater.

To reproduce, interspecific obligate brood parasites must locate the nests of target species in a time window appropriate for their eggs to be incubated successfully. While searching for nests, brood parasites may encounter nests that are at stages beyond the period for successful parasitism (e.g., too far into the incubation period or with young). For the Common Cuckoo (Cuculus canorus) and cowbirds of the genus Molothrus, the destruction of nest contents beyond the stage suitable for parasitism has been suggested to represent either predation, when the nest contents are consumed, or “nest farming” behavior (Arcese et al. 1992, 1996; Peer and Sealy 1999; Swan et al. 2015; Šulc et al. 2020) wherein the target species may renest. Nest farming is distinct from nest predation in that the behavior is hypothesized to provide a potential fitness benefit via creation of later opportunities for nest parasitism (Scott et al. 1992, Sealy 1994). Alternatively, the destruction of host nests where parasitic eggs were rejected by hosts is referred to as a retaliatory “mafia” behavior that can reinforce host acceptance of parasitic eggs (Zahavi 1979; in Brown-headed Cowbird [Molothrus ater], see Hoover and Robinson [2007]).

During our research on the nesting ecology of grassland birds (Renfrew and Ribic 2003, Renfrew et al. 2005, Ribic et al. 2012, Ellison et al. 2013, Byers et al. 2017), we used nest cameras to identify nest predators and recorded several cases of the destruction of nest contents by Brown-headed Cowbird, hereinafter referred to as cowbirds. Recordings of cowbirds at the nests of grassland birds are of interest because they document a poorly described behavior that can have important consequences for hosts and for the evolution of host–parasite behavior (Pietz and Granfors 2000, Granfors et al. 2001). Our study adds to records of cowbirds removing nestlings made at 10 unparasitized nests (Granfors et al. 2001, Stake and Cavanagh 2001) recorded in grassland and savanna systems.

Here we present behavioral data from our recordings of cowbird destruction of nest contents. For context, we provide cowbird parasitism rates and parasitism intensity for the passerine bird species we monitored in grasslands in southwest Wisconsin.

We used nest records and digital files from video recording systems at the nest from Renfrew and Ribic (2003), Ribic et al. (2012), Ellison et al. (2013), and Byers et al. (2017). All studies were done in southwestern Wisconsin, USA, and study sites were clustered near Mount Horeb (43.0167°N, 89.7500°W). Four grassy field types were studied: continuously grazed pasture, prairie, and cool- and warm-season grass fields. Over all studies, 46 pastures were sampled with sizes ranging from 10.2 to 163.8 ha, 12 prairie sites were sampled with sizes ranging from 4 to 267 ha, 38 cool-season grass fields were sampled with sizes ranging from 10.7 to 153 ha, and 10 warm-season grass fields were sampled with sizes ranging from 8 to 124.8 ha.

Over all studies, nest searching occurred between the beginning of May and early August. All nests were assigned a fate (success or failure) by the original researchers. In general, the original researchers used cues such as egg remains, missing, disturbed, or destroyed nest, and dead nestlings to indicate nest failure while presence of feather sheaths, feces in the nest, and chipping adults indicated nest success. The presence of cowbird eggs or nestlings was recorded at each nest visit. Nest visitation rate varied between 1 and 4 d.

We used video recording systems at nests to identify nest predators in all the studies. We prioritized putting video systems on nests of obligate grassland birds, followed by facultative grassland birds, and finally generalist birds that occurred in the grasslands (Sample and Mossman 1997). In general, we recorded continuously (24 h) using cameras with infrared light-emitting diodes (LEDs) that facilitated recording quality images under low-light conditions (Renfrew and Ribic 2003). We followed many of the recommendations of Richardson et al. (2009) for deploying cameras and we distributed cameras among fields to avoid clustering. We set up cameras at nests during or soon after the egg-laying stage ended to lower the chance for abandonment (Thompson et al. 1999, Renfrew and Ribic 2003). We deployed cameras on nests that had already hatched only when nests with eggs were not available.

Recording systems were attached to cameras with 25 m cables (following the protocol established by Renfrew and Ribic [2003]). Each camera was mounted on a wooden dowel 3–38 cm above the ground. Cameras were 64 cm3 and placed 12–25 cm from the nest, depending on the nest structure and surrounding vegetation. The field of view at these distances ranged from 414 to 1,320 cm3. Cameras were typically placed at or below the height of surrounding vegetation to avoid creating a potential visual cue for potential predators. Across studies, cameras were placed on 695 nests of passerine bird species (585, 35, and 75 nests of obligate grassland birds, facultative grassland birds, and generalist birds, respectively) resulting in 159,600 h of digital recordings (133,008, 8,040, and 18,552 h for obligate grassland birds, facultative grassland birds, and generalist birds, respectively; details by species in Supplemental Table S1).

As part of data analysis for each project, and other projects that entailed use of the video footage (e.g., Slay et al. 2012, Ribic et al. 2021), we watched the digital recordings of all nests to document nest fate, any events that resulted in loss of an egg or nestling (e.g., partial depredations), and any non-predatory events (e.g., visits, scavenging) and compiled this information in a master database. We watched the digital recordings using VideoLAN VLC Media Player or DivX Player. For this study, we searched the master database and used any depredation event that involved a cowbird.

We re-watched digital recordings to determine details about the timing of the arrival and departure of the cowbird with respect to the host species. Specifically, we noted the time when the host species left the nest (either before the cowbird arrived or as the cowbird arrived), time when the cowbird arrived, time when the cowbird departed, and time when the host species returned (while the cowbird was still at the nest or after the cowbird left). All observation times were translated to time relative to local sunrise in decimal hours because sunrise varies across the season. Times of local sunrise were determined from the U.S. Naval Observatory (2016). The duration of the event was defined as the elapsed time between when the cowbird arrived at the nest and the time the cowbird departed. If the duration of an event was not the same as the time it took the cowbird to remove the nest contents (i.e., removal time), we calculated the removal time separately for that event.

We documented the fate of the nests, any other cowbird activities that did not involve removing nest contents, and any other events that contributed to the fate of the nest. An event could consist of a single trip (i.e., the cowbird removed the nest contents without leaving the nest before departing) or multiple trips (e.g., the cowbird removed nest contents by sequentially carrying eggs/nestlings away from the nest before leaving without returning). The digital recordings of the cowbird events are available at Ribic and Ellison (2024).

We calculated parasitism rates for species that had at least 10 nests overall. Following Shaffer et al. (2019), parasitism rate was the number of parasitized nests divided by the total number of nests. We also calculated the median and range of number of cowbird eggs in a parasitized nest (i.e., parasitism intensity; McGeen 1972).

We documented 549 depredation events leading to the loss of an egg and/or nestling (partial or complete nest predations, scavenging of unhatched eggs). Out of those events, there were 7 events (1.3%) where cowbirds removed nest contents; 6 were at active nests and 1 was at an empty nest (Table 1). All the cowbirds were identified as female. The host species was never at the nest when the cowbird arrived. Among the active nests, cowbirds arrived at the nest an average of 3.8 min (SE = 1.6, n = 6, range 0.7–11.6) after the host species left; although the empty nest was visited by a host species prior to the cowbird event, the nest was not being attended by that time (Table 1, footnote c). Cowbirds removed nest contents during the early morning (mean = 3.9 h after sunrise, SE = 0.3 h, n = 4) or late afternoon (mean = 13.1 h after sunrise, SE = 0.4 h, n = 3), taking an average of 0.7 min (SE = 0.1 min, n = 7, range 0.4–1.1 min) to remove nest contents (note that duration was equivalent to removal time except for one nest; Table 1, footnote g). Cowbirds sequentially moved nest contents away from the nest (out of camera range) in 4 of the 7 events, taking an average of 3.0 trips (SE = 0.6, n = 4, range 2–4) to do so (Table 1, footnote g). All the cowbirds left before the host species returned, leaving the nest an average of 3.4 min (SE = 1.7, n = 6, range 0.5–10.7 min) before the host species arrived back at the nest.

Table 1.

Host egg and nestling destruction by Brown-headed Cowbirds (Molothrus ater) (Cowbird) at nests of songbirds in grasslands monitored with video recording systems in southwest Wisconsin, 1998–2011. Cowbird arrival time is time relative to local sunrise. Trips are the number of times the cowbird arrived and departed the nest while the host species was not present. Scientific names are listed in Supplemental Table S1.

Host egg and nestling destruction by Brown-headed Cowbirds (Molothrus ater) (Cowbird) at nests of songbirds in grasslands monitored with video recording systems in southwest Wisconsin, 1998–2011. Cowbird arrival time is time relative to local sunrise. Trips are the number of times the cowbird arrived and departed the nest while the host species was not present. Scientific names are listed in Supplemental Table S1.
Host egg and nestling destruction by Brown-headed Cowbirds (Molothrus ater) (Cowbird) at nests of songbirds in grasslands monitored with video recording systems in southwest Wisconsin, 1998–2011. Cowbird arrival time is time relative to local sunrise. Trips are the number of times the cowbird arrived and departed the nest while the host species was not present. Scientific names are listed in Supplemental Table S1.

For nests with nestlings, the cowbirds were seen rapidly pecking the nestlings in 3 of the 5 events. We could see both the nestling and the cowbird in 2 of the events. In the first event, the entire attack was on camera and the cowbird pecked the back, side, abdomen, chest, and head of the nestling (Table 1, footnote d). In the second event, only part of the attack was in view, but from what was seen, the cowbird pecked the leg, wing, side, and abdomen of the nestling (Table 1, footnote f). No puncture wounds were evident in either event. In both events, although the nestlings were alive after the cowbirds departed, both nestlings succumbed to their injuries within 24 h of the event.

Of the 6 active nests, cowbird damage of nest contents directly resulted in the failure of only 1 nest (Table 1). Three nests went on to fledge the remaining host young, while 2 failed due to other causes (Table 1). In only one instance did a cowbird come back to a nest after the event was finished, and the host species had returned. At that nest (Table 1, footnote a), a cowbird came back to the nest 12 min before sunrise to look at the empty nest and then a cowbird came back 4 min before sunrise and laid an egg. The host species had departed 0.7 min and 3.4 min before the cowbird visit and egg laying, respectively. The cowbird laid from a standing posture.

Overall, we recorded regular but low levels of parasitism by cowbirds among the nests of 11 songbird species (Table 2). Average parasitism rate of the 7 obligate grassland songbird species was 10% (SE = 3%, n = 7) with Henslow’s Sparrow (Centronyx henslowii) and Bobolink (Dolichonyx oryzivorus) having the lowest rates (<5%) and Western Meadowlark (Sturnella neglecta) and Dickcissel (Spiza americana) having the highest rates (20%; Table 2). Of the 4 facultative and generalist species, we found that Field Sparrow (Spizella pusilla) and Song Sparrow (Melospiza melodia) were the species most parasitized (>15%) with no parasitism among the nests of Clay-colored Sparrow (Spizella pallida; Table 2). Median number of cowbird eggs in a parasitized nest varied between 1 and 2 among the 10 parasitized songbird species (Table 2).

Table 2.

Brown-headed Cowbird (Molothrus ater) parasitism rate (% parasitized), total monitored nests (Nests), and median and range of cowbird eggs/parasitized nest by species and overall for passerine birds nesting in grassy fields in southwest Wisconsin, 1998–2011. Species are ordered by parasitism rate within the categories. Scientific names are listed in Supplemental Table S1.

Brown-headed Cowbird (Molothrus ater) parasitism rate (% parasitized), total monitored nests (Nests), and median and range of cowbird eggs/parasitized nest by species and overall for passerine birds nesting in grassy fields in southwest Wisconsin, 1998–2011. Species are ordered by parasitism rate within the categories. Scientific names are listed in Supplemental Table S1.
Brown-headed Cowbird (Molothrus ater) parasitism rate (% parasitized), total monitored nests (Nests), and median and range of cowbird eggs/parasitized nest by species and overall for passerine birds nesting in grassy fields in southwest Wisconsin, 1998–2011. Species are ordered by parasitism rate within the categories. Scientific names are listed in Supplemental Table S1.

In our study, in all instances of nest content destruction, Brown-headed Cowbirds arrived at nests after sunrise (outside of their normal laying period; Ellison and Sealy 2007) and, for the events at active nests, avoided interacting with the host species by arriving at nests after the host species had departed and leaving before the host species returned. However, other studies (Granfors et al. 2001, Stake and Cavanagh 2001, Šulc et al. 2020) did record instances of nest defense, indicating that interaction between the host and parasitic species can occur. Those studies (Granfors et al. 2001, Stake and Cavanagh 2001, Šulc et al. 2020) also noted that even with host nest defense, the parasitic species persisted in removing nest contents.

We found that cowbirds took a very short time (mean = 0.7 min) to remove nest contents. This is comparable to the 1.0 min average duration for Brown-headed Cowbird removal of nest contents at Black-capped Vireo (Vireo atricapilla) and Golden-cheeked Warbler (Setophaga chrysoparia) nests (table 1 in Stake and Cavanaugh [2001]). Granfors et al. (2001) noted that it took 1–2 min to remove nest contents at 3 grassland bird nests. Sequential removal of nest contents was noted by Stake and Cavanaugh (2001) and Šulc et al. (2020). While there have been a few eyewitness observations of nestlings with open wounds (table 1 in Šulc et al. [2020]), we did not find any evidence of puncture wounds on nestlings from cowbird pecking; likely the nestlings in our study died from blunt force trauma. Hematomas and internal bleeding on ejected nestlings were observed in a few eyewitness observations (table 1 in Šulc et al. [2020]).

Similar to Stake and Cavanagh (2001), we recorded egg and nestling removal by cowbirds later in the day relative to the timing for Brown-headed Cowbird egg laying recorded elsewhere (all before sunrise at 14 sites, n = 78; Ellison and Sealy 2007). In addition, our recording of an egg being laid (within the timing for Brown-headed Cowbird laying; Ellison and Sealy 2007) from a standing position is similar to how cowbirds lay eggs at nests on different substrates (Ellison et al. 2019).

We found that the damage of nest contents by cowbirds most often resulted in partial clutch or brood reduction that was relatively ineffective at causing potential hosts to renest. Our findings are similar to what was found by others (Granfors et al. 2001, Stake and Cavanagh 2001, Šulc et al. 2020). So, why cowbirds exhibit destructive behaviors toward nestlings and eggs remains enigmatic (Šulc et al. 2020). Certainly, the more frequently recorded behavior of egg removal prior to nest parasitism appears adaptive as the behavior can allow for an assessment of host egg development (Nakamura and Cruz 2000), decrease host detection of parasitism, increase incubation efficiency for the cowbird egg (Peer and Bollinger 2000), and reduce nestling competition for the potential cowbird nestling (see Antonson et al. [2022]). Our observations were consistent with those of Turner et al. (2022), suggesting that cowbird nest content destruction did not involve mafia-like retaliation by cowbirds on potential hosts for rejecting prior parasitism, as we did not record any prior parasitism at the 7 nests where destruction behavior was observed.

Cowbird destruction of nest contents without them being consumed, leading to abandonment of that nest attempt, can support nest farming hypotheses but depends on documenting that the affected hosts renest. Our studies lacked banded birds to track any subsequent nesting by individuals. However, all 7 cowbird nest depredations occurred before 25 June in our study, whereas the latest nests were initiated in July (Wolcott et al. 2023), suggesting adequate time was available for potential hosts to have nested again. It is less clear what costs to cowbirds might arise, other than attacks during nest defense, for cases that involve destruction of nest contents too late in a breeding season for potential hosts to renest or after nests become inactive but still contain eggs. Perhaps nest content destruction, regardless of seasonal timing, is a more adaptive strategy that can occasionally lead to nest “farming.” Our observations add to a growing number of video-recorded behaviors of brood parasites that can provide data for better testing hypotheses about nest destruction behavior.

We thank our research collaborators—T.J. Anderson, C. Byers, J. Dadisman, H. Doyle, M.J. Guzy, J.L. Nack, and D. Schneider—who ran the field projects, and all the field technicians who helped collect the data. We thank B. Peer, P. Pietz, and N. Antonson for their reviews of earlier drafts of this manuscript. We thank M. Šulc for encouraging us to publish these observations. No new data were collected for this study. The original projects were conducted in compliance with the Guidelines to the Use of Wild Birds in Research. Data collection for the projects occurred under protocols A01023, A01410, and A1210 approved by the Animal Care and Use Committee of the University of Wisconsin-Madison. We thank the funders of the original projects, the U.S. Fish and Wildlife Service, and Wisconsin Department of Natural Resources.

Antonson
ND,
Schelsky
WM,
Tolman
D,
Kilner
RM,
Hauber
ME.
2022
.
Niche construction through a Goldilocks principle maximizes fitness for a nest-sharing brood parasite
.
Proceedings of the Royal Society B
.
289
:
20221223
.
[PubMed]
Arcese
P,
Smith
JNM,
Hochachka
WM,
Rogers
CM,
Ludwig
D.
1992
.
Stability, regulation, and the determination of abundance in an insular Song Sparrow population
.
Ecology
.
73
:
805
822
.
Arcese
P,
Smith
JN,
Hatch
MI.
1996
.
Nest predation by cowbirds and its consequences for passerine demography
.
Proceedings of the National Academy of Sciences
.
93
:
4608
4611
.
Byers
CM,
Ribic
CA,
Sample
DW,
Dadisman
JD,
Guttery
MR.
2017
.
Grassland bird productivity in warm season grass fields in southwest Wisconsin
.
American Midland Naturalist
.
178
:
47
63
.
Ellison
KS,
Fiorini
VD,
Gloag
R,
Sealy
SG.
2019
.
Video recordings of Brown-headed (Molothrus ater) and Shiny (M. bonariensis) cowbirds reveal oviposition from an elevated position: Implications for host–parasite coevolution
.
Wilson Journal of Ornithology
.
131
:
789
795
.
Ellison
KS,
Ribic
CA,
Sample
DW,
Fawcett
MJ,
Dadisman
JD.
2013
.
Impacts of tree rows on grassland birds and potential nest predators: A removal experiment
.
PLOS One
.
8
:
e59151
.
Ellison
K,
Sealy
SG.
2007
.
Small hosts infrequently disrupt laying by Brown‐headed Cowbirds and Bronzed Cowbirds
.
Journal of Field Ornithology
.
78
:
379
389
.
Granfors
DA,
Pietz
PJ,
Joyal
LA.
2001
.
Frequency of egg and nestling destruction by female Brown-headed Cowbirds at grassland nests
.
Auk
.
118
:
765
769
.
Hoover
JP,
Robinson
SK.
2007
.
Retaliatory mafia behavior by a parasitic cowbird favors host acceptance of parasitic eggs
.
Proceedings of the National Academy of Sciences
.
104
:
4479
4483
.
McGeen
DS.
1972
.
Cowbird–host relationships
.
Auk
.
89
:
360
380
.
Nakamura
TK,
Cruz
A.
2000
. The ecology of egg-puncture behavior by the Shiny Cowbird in southwestern Puerto Rico. In:
Smith
JN,
Cook
TL,
Rothstein
SI,
Robinson
SK,
Sealy SG
, editors.
Ecology and management of cowbirds and their hosts: Studies in the conservation of North American passerine birds
.
Austin (TX)
:
University of Texas Press
;
178
186
.
Peer
BD,
Bollinger
EK.
2000
. Why do female Brown-headed Cowbirds remove host eggs? A test of the incubation efficiency hypothesis. In:
Smith
JN,
Cook
TL,
Rothstein
SI,
Robinson
SK,
Sealy
SG
, editors.
Ecology and management of cowbirds and their hosts: Studies in the conservation of North American passerine birds
.
Austin (TX)
:
University of Texas Press
;
187
192
.
Peer
BD,
Sealy
SG.
1999
.
Laying time of the Bronzed Cowbird
.
Wilson Bulletin
.
111
:
137
139
.
Pietz
PJ,
Granfors
DA.
2000
.
Identifying predators and fates of grassland passerine nests using miniature video cameras
.
Journal of Wildlife Management
.
64
:
71
87
.
Renfrew
RB,
Ribic
CA.
2003
.
Grassland passerine nest predators near edges based on video footage
.
Auk
.
120
:
371
383
.
Renfrew
RB,
Ribic
CA,
Nack
JL.
2005
.
Edge avoidance by nesting grassland birds: A futile strategy in a fragmented landscape
.
Auk
.
122
:
618
636
.
Ribic
C,
Ellison
K.
2024
.
Digital records of Brown-headed Cowbirds removing eggs and nestlings from nests of grassland passerine birds in southwest Wisconsin
[
dataset]
. Dryad.
Ribic
CA,
Guzy
MJ,
Anderson
TA,
Sample
DW,
Nack
JL.
2012
.
Bird productivity and nest predation in agricultural grasslands
.
Studies in Avian Biology
.
43
:
119
134
.
Ribic
CA,
Rugg
DJ,
Ellison
K,
Koper
N,
Pietz
PJ.
2021
.
Diel patterns of predation and fledging at nests of four species of grassland songbirds
.
Ecology and Evolution
.
11
:
6913
6926
.
Richardson
TW,
Gardali
T,
Jenkins
SH.
2009
.
Review and meta-analysis of camera effects on avian nest success
.
Journal of Wildlife Management
.
73
:
287
293
.
Sample
DW,
Mossman
MJ.
1997
.
Managing habitat for grassland birds: A guide for Wisconsin
.
Madison (WI)
:
Wisconsin Department of Natural Resources
.
Scott
DM,
Weatherhead
PJ,
Ankney
CD.
1992
.
Egg-eating by female Brown-headed Cowbirds
.
Condor
.
94
:
579
584
.
Sealy
SG.
1994
.
Observed acts of egg destruction, egg removal, and predation on nests of passerine birds at Delta Marsh, Manitoba
.
Canadian Field-Naturalist
.
108
:
41
51
.
Shaffer
JA,
Igl
LD,
Johnson
DH.
2019
.
The effects of management practices on grassland birds—Rates of Brown-headed Cowbird (Molothrus ater) parasitism in nests of North American grassland birds
.
Reston (VA)
:
DOI, U.S. Geological Survey
.
Professional Paper
1842
-PP.
Slay
CM,
Ellison
KS,
Ribic
CA,
Smith
KG,
Schmitz
CM.
2012
.
Nocturnal activity of nesting shrubland and grassland passerines
.
Studies in Avian Biology
.
43
:
105
116
.
Stake
MM,
Cavanagh
PM.
2001
.
Removal of host nestlings and fecal sacs by Brown-headed Cowbirds
.
Wilson Bulletin
.
113
:
456
459
.
Šulc
M,
Štětková
G,
Jelínek
V,
Czyż
B,
Dyrcz
A,
.
2020
.
Killing behaviour of adult brood parasites
.
Behaviour
.
157
:
1099
1111
.
Swan
DC,
Zanette
LY,
Clinchy
M.
2015
.
Brood parasites manipulate their hosts: Experimental evidence for the farming hypothesis
.
Animal Behaviour
.
105
:
29
35
.
Thompson
FR
III,
Dijak
W,
Burhans
DE.
1999
.
Video identification of predators at songbird nests in old fields
.
Auk
.
116
:
259
264
.
Turner
AM,
Hauber
MW,
Reichard
DG.
2022
.
Twenty-two years of brood parasitism data do not support the mafia hypothesis in an accepter host of the Brown-headed Cowbird (Molothrus ater)
.
Journal of Field Ornithology
.
93
(
4
):
4
.
U.S. Naval Observatory
.
2016
.
Sun or moon rise/set table for one year
. https://aa.usno.navy.mil/data/docs/RS_OneYear
Wolcott
DM,
Herkert
JR,
Ribic
CA,
Renfrew
RB,
Sample
DW.
2023
.
Potential impacts of land-management schedules on grassland bird nests and fledglings
.
Wildlife Society Bulletin
.
47
(
4
):
e1488
.
Zahavi
A.
1979
.
Parasitism and nest predation in parasitic cuckoos
.
American Naturalist
.
113
:
157
159
.

Supplementary data