Complete Sanitation of Dead Nestlings by Parent Birds May Bias Nest Depredation Rates

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Complete Sanitation of Dead Nestlings by Parent
Birds May Bias Nest Depredation Rates Chris
Kirkpatrick1, Courtney J. Conway2, and Moez H.
Ali1 1 University of Arizona 2 USGS Arizona
Cooperative Fish and Wildlife Research Unit

• RESULTS (CONTINUED)
• Daily nest survival (DNS) was lower for all
  RFWA and YEJU nests (n 17) monitored during the
  5-day period before the storms compared to the
  5-day period after the storms.
• DNS pre-storm 1.0 (SE 0) Z 1.8
• DNS post-storm 0.938 (SE 0.036) P 0.07
• Sixty-seven percent of nests that failed after
  the storms were incorrectly identified by field
  personnel as having been depredated (video
  footage revealed these nests failed due to
  weather and were later sanitized by parent
  birds).

ABSTRACT Estimates of avian nesting success
typically assume that nests found to be empty and
intact (i.e., nest cup and lining undisturbed
Fig. 1) prior to fledging are likely to have been
depredated. We provide evidence that an empty
nest may not always indicate a depredated nest,
but instead may result from complete sanitation
of dead nestlings by parent birds. In 2006, we
used time-lapse video cameras to monitor nests of
red-faced warblers (Cardellina rubrifrons Fig.
2) and yellow-eyed juncos (Junco phaeonotus Fig.
2) in high-elevation, mixed-conifer forests of
the Santa Catalina Mountains, Arizona. Following
rain and hail storms on 4 5 July 2006, video
footage revealed that parent yellow-eyed juncos
and red-faced warblers removed all nestlings from
2 nests (the nestlings apparently died after the
storms). Our results indicate that complete
sanitation of dead nestlings by parent birds may
be a relatively common behavior, suggesting that
researchers use caution when assigning fates to
empty nests during future nest-monitoring
studies.
Figure 2. Yellow-eyed junco (YEJU left) and
red-faced warbler (RFWA right) - 2
ground-nesting birds that breed in close
association in southeastern AZ.
Bruce Taubert
Bruce Taubert

• DISCUSSION
• We provide evidence that an empty, intact nest
  may not always indicate a nest depredation, but
  instead may result from complete sanitation of
  dead nestlings by parent birds following
• inclement weather.
• Inclement weather can lead to complete brood
  mortality (Stewart 1972) and young (1-8 day old)
  nestlings are especially susceptible because of
  their inability to maintain constant body
  temperature (Dunn 1976).
• Preliminary results suggest that complete
  sanitation of dead nestlings by parent birds may
  be a relatively common behavior in red-faced
  warblers and yellow-eyed juncos.
• The frequency with which this behavior may occur
  in other species is unknown. However, complete
  brood mortality and subsequent sanitation of dead
  nestlings is likely to occur
• 1) following strong storms
• 2) at nests that are prone to flooding
• 3) when nestlings are young and brood sizes
• are small (Dunn 1976)
• Researchers should use caution when assigning
  fates to empty, intact nests (especially after
  inclement weather) given that the incorrect
  assignment of nests fates has the potential to
  bias nest depredation rates.

• RESULTS
• Two nests (1 RFWA and 1 YEJU) that were
  monitored continuously by video cameras and
  checked periodically by field personnel failed in
  early July 2006 (Table 1).
• Both nests contained young nestlings (1-4 days
  old) prior to failure.
• Field observers assumed that the RFWA nest had
  been depredated (the nest was empty and intact)
  and the YEJU nest had been partially depredated
  (the nest had 1 infertile egg and was intact).
• Video footage showed parent birds sanitizing
  nests by removing the entire brood of dead
  nestlings (Fig. 3).
• Precipitation and temperature data from 2 local
  weather stations (Figs. 4 5 Pima County 2006)
  indicated that strong storms occurred on 4 5
  July 2006, 1-2 days before the failure of both
  nests.

• STUDY AREA
• 5 16-20 ha plots located in high-elevation
  (2,300-2,800 m), mixed-conifer forest of the
  Santa Catalina Mountains, Arizona.
• Mean annual precipitation in the Santa Catalina
  Mountains is 26.8 inches (Brown 1994) with most
  precipitation falling during a brief season of
  strong thunderstorms that begins in early July.
• METHODS
• From April-July 2006, we monitored a total of
  148 red-faced warbler and yellow-eyed junco nests
  using standard nest-monitoring protocols (Martin
  and Geupel 1993).
• We used time-lapse video cameras to continuously
  monitor a subset of 18 nests during the
  incubation and nestling periods.
• We compared estimates of daily nest survival
  (Mayfield 1961, 1975) during a 5-day period
  before and during a 5-day period after strong
  thunderstorms on 4 5 July 2006.

ACKNOWLEDGMENTS We thank M. Eastwood, N.
Nardello, and T. Selvidge for assistance locating
nests and operating video cameras and S. Sferra
(Bureau of Reclamation) for the loan of the video
cameras. Funding was provided by the U.S. Fish
and Wildlife Service and the U.S. Geological
Survey. LITERATURE CITED Brown, D. E. 1994.
Biotic Communities Southwestern United States and
Northwestern Mexico. University of Utah Press,
Salt Lake City, Utah. Dunn, E. H. 1976. The
relationship between brood size and effective
homeothermy in nestling house wrens. Wilson
Bull. 88478-482. Martin, T. E., and G. R.
Geupel. 1993. Nest-monitoring plots methods for
locating nests and monitoring success. Journal
of Field Ornithology 64507-519. Mayfield, H.
1961. Nesting success calculated from exposure.
Wilson Bull. 73255-261. Mayfield, H. 1975.
Suggestions for calculating nest success. Wilson
Bull. 87456-466. Pima County. 2006. Pima
County ALERT System. http//rfcd.pima.gov/alertsy
s/ Stewart, R. M. 1972. Nestling mortality in
swallows due to inclement weather. Ca. Birds
369-70.