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Identifying Predators and Fates of Grassland Passerine Nests Using Miniature Video Cameras

Tables


Table 1.  Number of nests monitored with and without cameras and exposure days used for survival analyses of grassland passerine nests in Stutsman and Barnes Counties, North Dakota, 1996-97.
Species Camera No camera
Nests Exposure daysa Nests Exposure daysb
Incubation Nestling Incubation Nestling
Sedge wren (Cistothorus platensis) 0     1 6.0 13.0
Sprague's pipit (Anthus spragueii) 0     1 1.0 12.0
Common yellowthroat (Geothlypis trichas) 1 7.0 3.0 1 5.0 10.0
Clay-colored sparrow (Spizella pallida) 34 36.0 96.5 186 750.0 758.0
Vesper sparrow (Pooecetes gramineus) 1 3.0 0.0 1 2.0 0.0
Savannah sparrow (Ammodramus sandwichensis ) 7 17.0 42.0 18 30.0 85.0
Grasshopper sparrow (Ammodramus savannarum) 4 0.0 23.0 6 20.0 24.0
Baird's sparrow (Ammodramus bairdii) 3 0.0 10.5 4 1.0 25.5
Nelson's sharp-tailed sparrow (Ammodramus nelsoni) 0     1 2.0 10.0
Song sparrow (Melospiza melodia) 2 2.5 9.0 8 28.5 18.0
Chestnut-collared longspur (Calcarius ornatus) 9 22.0 37.5 47 217.0 277.5
Bobolink (Dolichonyx oryzivorus) 5 16.0 33.0 17 116.5 90.0
Western meadowlark (Sturnella neglecta) 3 1.0 3.0 4 17.0 17.0
Total 69 104.5 257.5 295 1196.0 1340.0
a Exposure days calculated as if nests were on the same visitation schedule as nests without cameras.
b Some exposure days are from nests that were subsequently monitored with cameras.

Table 2.  Videotaped fates of eggs and nests during incubation for 10 grassland passerine species in Stutsman and Barnes Counties, North Dakota, 1996-97.
Nest fate No. Nests No. eggs
Hatched Deada Depredated Abandoned Unknown Total
Hatched 23 85 8 2 0 0 95
Depredated 7 0   25 0 0 25
Abandoned 15 0   8b 52 0 60
Censoredc 3         13 13
Total 48 85 8 35 52 13 193
a Infertile or dead embryo.
b Eggs destroyed by cowbirds at unattended nests.
c Camera system failed (n = 2) or removed (n = 1) before predicted hatch date.

Table 3.  Videotaped fates of hatched nests and nestlings for 9 grassland passerine species in Stutsman and Barnes Counties, North Dakota, 1996-97.
Nest fate No. nests No. nestlings
Fledged Died Unknown Total
Normal Forceda Depredated Fell out Starved Abandoned
Fledgedb 23 67c 1 7 1 0 0 1 77
Force fledged 5 0 7 8 0 0 0 0 15
Depredated 10 0 0 38 0 0 0 1 39
Fell over 1 0 0 0 4 0 0 0 4
Starved 1 0 0 0 0 3 0 0 3
Abandoned 1 0 0 0 0 0 3 0 3
Censoredd 3     5       6 11
Total 44 67 8 58 5 3 3 8 152
a Left nest during or <6 min following depredation of nest mates.
b ≥1 nestling fledged normally.
c Includes 3 nestlings that fledged <1 min after researcher visit and 2 nestlings from 1 nest that left prematurely for unknown reasons.
d Camera system failed (n = 2) or removed (n = 1) before predicted fledge date.

Table 4.  Two daily survival rate estimatesa, with 95% confidence intervals, for grassland passerine nests monitored with cameras in Stutsman and Barnes Counties, North Dakota, 1996-97.
Nest stage Method Survival rate
Daily 95% confidence interval
Incubation Simulated Mayfield 0.9139 0.8601-0.9677
Mayfield 0.9320 0.8834-0.9806
Nestling Simulated Mayfield 0.9417 0.9131-0.9704
Mayfield 0.9431 0.9160-0.9702
a Simulated Mayfield estimates were calculated using nest fates based on sign at nests and exposure days based on simulated nest visits. Mayfield estimates were calculated using actual nest fates and exposure days determined from videotapes.

Table 5.  Diurnal and nocturnal initial-predation rates (IPR)a for camera-monitored grassland passerine nests in relation to stage, type, and height of nests in Stutsman and Barnes Counties, North Dakota, 1996-97.
Characteristic Exposure days Diurnal predation Nocturnal predation
No. of depredated
nests
Daily IPR SE No. of depredated
nests
Daily IPR SE
Nest stage
    Incubation 100 4 0.0400 0.0196 2 0.0200 0.0140
    Nestlingb 274 14 0.0511 0.0133 6 0.0219 0.0088
Nest type
    Open 187 14 0.0749c 0.0192 3 0.0160 0.0092
    Covered 187 4 0.0214c 0.0106 5 0.0267 0.0118
Nest height
    Ground 211 8 0.0379 0.0131 6 0.0284 0.0114
    Aboveground 163 10 0.0613 0.0188 2 0.0123 0.0086
a Daily predation rate censoring exposure days after the first predation event. Diurnal predation events occurred after sunrise and before sunset; nocturnal events occurred after sunset and before sunrise.
b Includes 3 nests with partially hatched clutches, all depredated during the day.
c Diurnal initial-predation rate differed between open and covered nests (χ²1 = 5.93, P = 0.015). No other diurnal or nocturnal pairwise comparisons were significant (χ²1 = 0.01-1.27, P = 0.26-0.91).

Table 6.  Types of sign left by predators at 26 grassland passerine nests monitored by cameras in Stutsman and Barnes Counties, North Dakota, 1996-97.
Predator No sign Egg shellsa Nest lining disturbed Nest bowl disturbed Hole in nest Nest bowl destroyed Total nestsb
Mouse (Peromyscus and Zapus)   2   1     2
Thirteen-lined ground squirrel (Spermophilus tridecemlineatus) 3 2 4 1 1   8
Franklin's ground squirrel (Spermophilus franklinii) 2       2 1 5
Long-tailed weasel (Mustela frenata)       1     1
American badger (Taxidea taxus) 2           2
Red fox (Vulpes vulpes)   1c         1
Red fox or coyote (Canis latrans) 1           1
White-tailed deer (Odocoileus virginianus) 2           2
Northern harrier (Circus cyaneus) 1           1
Hawk (Buteo sp.)           1 1
Brown-headed cowbird (Molothrus ater) 1d 1e         2
Unknownf           1 1
Noneg           2 2
a 12 nests had eggs when depredated.
b A nest may have more than one type of sign. Sign was not evaluated at 1 nest that was partially depredated by a mouse and 2 that were partially depredated by unknown predators because the final fate was not taped or the final fate was not the predation event.
c Scavenged eggs punctured by cowbird.
d Three of 4 clay-colored sparrow eggs removed; no cowbird eggs laid.
e Punctured meadowlark eggs; no cowbird eggs laid.
f Removed nestlings out of camera view from back of nest.
g Active nests that tipped over; would have been classified as depredated using information from nest visitation only.

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