White-tailed Deer (Odocoileus virginianus) Predation
on Grassland Songbird Nestlings
Results and Discussion
During four field seasons (1996-1999) we monitored 132 nests with cameras. Predation occurred at 57 of these nests; white-tailed deer depredated 4 (8%) of the 53 nests at which predators were identified. No evidence of predation (e.g., tracks, droppings, prey remains or disturbed vegetation) was observed at any of the nests depredated by deer.
Case 1.—On 21 July 1996 at 02:15:43 Central Daylight Time, an adult Savannah sparrow (Passerculus sandwichensis) flushed from a canopied ground nest that contained two sparrow nestlings and two brown-headed cowbird (Molothrus ater) nestlings about 7- d old. At 02:15:54 a deer appeared at the nest for 3 sec and removed one nestling from camera view. At 02:16:29, the deer was in view for 4 sec and removed a second nestling. From 02:16:44 to 02:16:54 one nestling moved out of the nest but was still in camera view; the deer caught it outside the nest at 02:17:01. At 02:17:14 the deer returned to the nest and removed the fourth nestling within 4 sec (Fig. 1A). At 02:17:30 the deer examined the empty nest for 5 sec. In short, the deer removed all four nestlings in 14 sec during a span of 1.4 min.
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| Fig. 1. (A) White-tailed deer (left eye, at arrow, and side of head visible) at canopied nest of Savannah sparrow that contained four 7-d-old nestlings. Nest was on the ground in planted grass; camera was 30 cm from nest. (B) Deer (top of muzzle) at canopied nest of grasshopper sparrow that contained three 8-d-old nestlings. Nest was on the ground in native prairie; camera was 13 cm from nest. (C) Deer (left side of muzzle; note black mark under lower lip) at open-bowl nest of clay-colored sparrow that contained three nestlings and one unhatched egg. Nest was 15 cm above the ground in a buckbrush (Symphoricarpos occidentalis) plant; camera was 18 cm from nest. (D) Deer (left side of muzzle) at open-bowl nest of red-winged blackbird that contained two nestlings and two eggs. Nest was 40 cm above the ground in buckbrush; camera was 23 cm from nest. Times on images are Central Daylight Time. |
Case 2.—On 5 July 1997 at 21:47, an adult grasshopper sparrow (Ammodramus savannarum) brought food to three 8-d-old nestlings in a canopied ground nest, then left with a fecal sac. A fourth nestling already had fledged about 3.5 h earlier. At 22:04:35 a deer appeared and removed two nestlings from the nest within 5 sec (Fig. 1B). At 22:04:46 the last nestling jumped from the nest and out of camera view. The deer inspected the nest for 6 sec at 22:04:56 and for 2 sec at 22:05:06. The adult sparrow returned to the empty nest bowl at 22:12 and remained in the nest until flushed at 23:34:46. A deer (possibly a different individual) nosed the empty nest at 23:34:59 for 4 sec and at 00:54:25 for 5 sec.
Case 3.—On 15 June 1998 at 05:11:39, a clay-colored sparrow (Spizella pallida) flushed from an open-bowl nest (15 cm above ground) that contained three 3-d-old nestlings and an unhatched egg. At 05:12:53 a deer was in view for 6 sec, during which time it put its nose in the nest but removed nothing. At 05:13:21 the deer's muzzle briefly passed over the nest; at 05:13:29 the deer put its nose in the nest for 6 sec and removed one nestling (Fig. 1C). The two remaining nestlings could be seen moving in the nest. At 05:17:45 the deer returned to the nest for 2 sec but did not remove any nestlings. At 05:22 an adult sparrow returned to the nest and resumed brooding. Later that morning only one nestling was moving; at 11:04 an adult sparrow removed the dead nestling. On 21 June the surviving nestling fledged; one unhatched egg remained in the nest.
Case 4.—On 30 June 1999 at 04:50:07, a red-winged
blackbird (Agelaius phoeniceus) flushed from an open-bowl nest (40 cm above
ground) that contained two 4-d-old nestlings (one blackbird, one cowbird) and
two unhatched eggs (one blackbird, one cowbird). At 04:50:11 a deer put its nose
in the nest, pulled the nest away from the camera momentarily and removed both
nestlings within 3 sec (Fig. 1D). The nest, still containing two unhatched eggs,
was abandoned by the blackbird later that morning.
These cases indicate that white-tailed deer depredate both ground and aboveground
songbird nests with open and covered bowls in grassland habitats. Although none
of the four nest bowls were damaged, at the smallest nest, which also had the
smallest nestlings (3-d-old clay-colored sparrows; Case 3), the deer seemed
to have difficulty removing the nestlings and eventually left two of them (one
dead). It is unclear why deer left all three eggs in the nests they depredated.
To test whether a deer would eat eggs, we placed four bobwhite quail (Colinus
virginianus) eggs in a group on the ground inside the 0.4-ha pen of a captive-reared
deer and monitored the deer's response remotely with one of our miniature cameras.
The deer mouthed an egg for a few seconds, removed one egg from camera view
about 40 min later, then removed the other three eggs one at a time during the
next 2 min. Although we could not see the deer ingest the eggs on tape, all
the eggs appeared to have been picked up whole, and no egg contents or shell
fragments remained.
The relative importance of deer as predators on grassland songbird nests is
difficult to judge because predator communities likely vary among sites and
years. However, among the predators we have identified, few species [notably
thirteen-lined ground squirrels (Spermophilus tridecemlineatus)] depredated
more nests than did deer (Pietz and Granfors, 2000). Lack of sign at most depredated
songbird nests (e.g., Thompson et al., 1999; Pietz and Granfors,
2000) makes it unlikely that deer predation will be detected without cameras
or direct observation.
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