Palila Restoration

TIME ALLOCATION OF NESTING PALILA: A VIDEO STUDY

Megan E. Laut, Paul C. Banko, Elizabeth M. Gray, and Leona L. Laniawe
USGS, BRD, Pacific Islands Ecosystem Research Center,
Kilauea Field Station, Hawaii National Park, HI

INTRODUCTION

We initiated a video study to quantify nesting behavior of palila (Loxioides baillieu) adults and to document causes of nest failure. The palila is an endangered Hawaiian honeycreeper whose current range is restricted to 5% of its original habitat on Mauna Kea, Hawaii. Palila are non-territorial, monogamous breeders that have adult male helpers at 30-50% of nests. In this male-biased population (1:1.8), males typically begin breeding at 3 years and females at 2 years. Breeding can occur any time of year, but the breeding season usually extends from March to September, with a peak number of nests in June.

The nesting cycle averages 41 days from first egg to fledging. Eggs hatch at 16 days and chicks fledge at approx. 25 days. Females often renest after nest failure and sometimes after successfully rearing a brood. Clutches consist of 2 to 3 eggs; of those, 56% of eggs hatch and 70% (x = 1.07 per nest) of chicks fledge. Causes of nest failure are predation by introduced mammals (cats and rats), abandonment, hatch failure, death in the nest, and rain storms. Population : wide breeding effort is greatly decreased in years of drought. Chicks are cared for up to 3 months after fledging, usually by a male.

METHODS

Data Collection

• Nests were located during the breeding seasons of 1991, 1993, and 1994 by systematic searches of transects on Mauna Kea, Hawaii.
• A black and white video camera with an external infrared illuminator connected to an 8mm Sony video recorder set at 10-s intervals was introduced to each nest over 1 to 2 days.
• The 2x3x5 inch camera was placed approximately 12 inches from the nest cup. Nests were recorded continuously (day and night) until the nestlings fledged or the nest failed. All videos contained a time and date stamp with the nest ID.
• The nest was visited approximately once every 3 days for regular nest checks and to change the videotape.

Sampling Method

• Videos were watched on a black and white monitor using a multi-speed video player.
  
• Behavior samples were taken every 60 seconds.
• Behaviors for the female were defined as follows:

Awake: eye open, or movements such as head turns, wing flutters, preening, and shifting position
Asleep: head tucked under wing or toward breast, or eye closed
Unknown:status undetermined due to camera angle, tape quality, or position in relation to the camera
On: incubation or brooding
Off: not on the nest
Visit: Adult (male, female or helper) near the rim of nest, potentially for a feeding event

• Nest breaks and feeding events were measured continuously so precise (+10 s) rates could be determined.

Data Analysis

• A nest was excluded from analyses in cases where fewer than 50 minutes were recorded in an hour (for hourly averages or rates), or fewer than 1200 minutes were recorded in a day (for daily averages).
• Rates for behaviors that occur only during the day such as feeding of nestlings and incubation breaks were adjusted for the number of daylight hours, so that results represent rates for 11 to 14 haour days.

RESULTS

Table 1: Seven nests were monitored. 64 percent fledged at least one chick.

Figure 1: Number of nest breaks decreased throughout the nesting cycle.

Figure 2: Length of nest breaks increased after hatching until 1 week before fledging, when breaks became shorter

Figure 3: Time off the nest increased after hatching until 1 week before fledging, when the female spent more time on the nest.

Day of Nest

Figure4: Number of nest visits by adults increased throughout the nesting cycle until 1 week before fledging, when the number of visits decreased.

Day of Nest

DISCUSSION

Egg Stage

• Number and length of nest breaks stayed relatively constant from days 1 to 16, as did the total number of minutes off the nest.

Post-Hatch

• Number of nest breaks decreased, as both the length of nest breaks and the total number of minutes off the nest increased. Adult feeding rates eased slightly.

Pre-Fledge (1 Week before Fledge)

• Length and number of nest breaks, and total time off the nest by the female decreased, as adult feeding rates decreased only slightly.

• During the post-hatch stage, care of young appears to be divided evenly between females and males. As fledging approaches (1 week before fledging), females spend less time feeding young; males, who are responsible for most fledgling care, appear to maintain the same amount of care.

FUTURE DIRECTIONS

• Technical complications made data collection difficult for portions of this study. Tape quality was poor in many recordings, and black and white recording prevented adult identification by band combinations.

We are currently conducting another video study during the 1999 breeding season. Recordings are in real time instead of time-lapse. More precise feeding rates and food types delivered by each of the adults attending the nest might be available, which may help us relate parental behavior to nest success.