The White Fairy Tern (Gygis alba) or the Manu-o-Kū is a threatened seabird indigenous to many islands throughout the Pacific (Vanderwerf 2003). While it commonly resides in less populated islands in the Pacific, within the main Hawaiian Islands the only recorded population has been observed on O’ahu since 1961 (Niethammer et.al. 1998, Vanderwerf 2003). As of 2007, the Manu-o-Kū is the official bird of the City and County of Honolulu, amplifying its cultural importance and making it more recognizable to the public. The species is listed as threatened by the State of Hawai’i and is protected under the Federal Migratory Bird Treaty Act. Manu-o-Kū in Honolulu lay one single egg directly on a tree branch (Vanderwerf 2003)
Since 2014, Kapi‘olani Community College (KCC) students have been monitoring Manu-o-Kū nesting locations and behavior on campus. From those efforts, other projects to research the terns have arose. My project is monitoring how the chicks grow and are raised. This is important because not much research has been done on how the Manu-o-Kū in Hawaii raise their chicks. By better understanding chick growth rate and parental care behavior, we can better understand how to conserve this incredible species and give others monitoring the terns and tree trimmers a better idea of the chicks age and when the nest will be considered inactive.
Figure 1 - Computer Recording Setup
Figure 2 - Balloon Measurement
Observations of the Manu-o-Kū were done at a minimum distance of ten meters using binoculars. Activity was recorded Monday through Friday mornings following sunrise on KCC campus. Nests were monitored, and location was noted. Once the eggs in the nests hatched, I would take pictures through a spotting scope every few days until the chick fledged. Once the chick fledged I used a balloon to send up a card with markings 1 cm apart from each other and took a picture (Figure 2). I put that picture into a program called Imagej (Abramoff et. al. 2004) and used the measurement from the card to set the scale. I measured the length of identifiable notches/imperfection on the branch. I then used those measurements to set the scale for the images with the chick to get an approximate measurement of the chicks: height, bill length, body length, tail length, and wing length. In some pictures I was even able to get measurements on one of the parents. One nest was in the perfect location to be recorded so, once the eggs in the nests hatched, I set up cameras within a building to monitor the parental care behaviors of Manu-o-Kū for two chicks at one nest site during different breeding events on Kapiolani Community College Campus. The cameras were connected to a computer which then recorded and livestreamed video. One camera was attached to a spotting scope for a close-up picture of the chick while the other was mounted to a railing to get a view of the entire branch. The videos were then reviewed at a later date and the activities of the adults were documented. Behaviors that were being monitored were: when parent(s) returned or left the nest site, allopreening (when parent preens chick), Courtship behaviors (when parents preen each other or Foot stomping), Feeding events and duration, and if the parent is sitting on the chick and for how long. I also noted when the chicks leave the screen and whether or not an adult is present off screen (off screen being when the chick or adult is on the larger screen). When documenting behaviors, I note what time in the video it occurs at for more in depth review or, so I can document what time of day the behavior occurs at.
Figure 4 - Nesting Map
Figure 5 - Nesting Timeline
Figure 6a - Body Length
Figure 6b - Tail Length
Figure 6c - Bill Length
Figure 6d - Wing Length
Figure 7a - Activities with Young Chicks
Figure 7b - Activities with Old Chicks
Over the course of one and a half years, a total of four chicks were monitored, photographed, and measured (Figure 3) two of which were also recorded with a remote video camera. One was measured during part of summer and the Fall 2016 semester, one during the Fall 2016 semester, one during the Spring 2017 semester and one over the Summer of 2017. All four chicks measured were from three different nesting sites, but all nests were on KCC campus (Figure 4). All four chicks were measured using the ImageJ program to get an approximate measurement of their height, bill length, body length, tail length, and wing length (Figure 6a-d). After analyzing my data, I have concluded that height is not a reliable measurement that can depict growth rate of the chick and has been removed. Of the four measured chicks, one chick grew larger in all aspects and more quickly in most aspects (except for tail length). Two of the chicks (from the same nesting site) grew at a very similar rate to one another except for in tail length. The difference in growth rate can be best seen in the comparison of tail length (Figure 6b). The recording of the third nest (a total of two chicks) totaled to over 1,000 hours of video, only about 95 hours of video between the two chicks were able to be analyzed using a video playing software and writing all activities down by hand.
When referring to “young” chicks I am referring to when the chicks are between 0 to 21 days old and “old” chicks is referring to chicks that are 22 to 44 days old. A breakdown of the adult’s activities can be seen in Figures 7a and 7b where “standing with chick” means the adult is on screen while exhibiting no notable behaviors, “away from nesting branch” means that the adult is off screen, and “exhibiting courtship behaviors” means that the adults are allopreening or foot stomping (those are the only courtship behaviors that were observed). By looking at Figure 7a-b, you can see that, on average, the parents would spend more time with the new chicks than they did with the old chicks. Analysis of the videos also showed that parents did not return at set times, sometimes returning in the middle of the night or the middle of the day with no food to offer and staying away from the chick.
The videos of the chicks showed that with new chicks, there was an adult on screen with the chick through a good portion of the night (~36.76% night is the time between sunset and sunrise) while with old chicks, the adult was hardly present at night (~6.62% of the night). On top of that, feedings would not occur at night, but showed no other pattern. Feedings seemed to occur whenever and with whatever the parents could catch with no pattern to age of chick or time of day which was observed across all the videos that I analyzed. Between the young chicks one received 4 feedings totaling 15 fish and the other received 9 feeding totaling 23 fish, between the old chicks one received 18 feedings totaling 24 fish (1 fish was dropped, and 1 feeding has an unknown amount) and the other received 6 feedings totaling 6 fish (3 feedings have an unknown amount) all during a 24-hour period. There are noticeable differences in other behaviors which can be seen in Figures 7a-b. You can see that the adults no longer sit on and spend less time standing with the old chicks and instead begin exhibiting courtship behaviors such as allopreening and foot stomping, a behavior not present with the young chicks.
Figure 3 - Chick Growth
It is exciting to be able to see how the parents treat the chick as it ages, and I can’t wait to go through all the videos to see how the behaviors vary between chicks (even though it is at the same nesting spot) and see if the amount of care, fish fed, and time hatched has any effect on the growth rate or final size of the chick. It was surprising to observe the differences in growth rates which may have occurred because one chick received more food. In Figure 6c there are measurements of two separate parents from two chicks which is closer in size to the chick at Kauila B. The adults being closer in size to the Kauila B chick could indicate that the measurements for Kauila B were more accurate, but, since the other three chicks were very similar in growth rate and size, it may mean that the measurements for Kauila B or the adult are inaccurate. The inconsistency between the chicks that I measured could be due to human or analysis error as I was unable to measure the chick directly. I still found that comparing the pictures of a chick of a known age to a chick of an unknown age can get you a very close approximation of the unknown chicks age. This may be due to the size of the chicks as well as their plumage. The data that has been collected has given better insight into white tern behaviors, nesting habits, and growth.
Figure 8 - Adult Preening Chick
In the future, I would hope to gather data on more nests and to improve my data collecting procedures so I can gather more accurate data that gives a more accurate representation of the chicks growth rate and care behaviors as well as seeing if the incubation time of the egg or the time of year the egg was laid has any affect on their growth rate and seeing if it’s possible to identify the fish that the Manu-o-Kū eat. My project can also include documenting the Manu-o-Kū chicks plumage as they age, Manu-o-Kū diet and protection of their food source, and if the tides/moon phases could have an effect on when the Manu-o-Kū return to land and/or their nests.
* Abramoff, M.D., Magalhaes, P.J., Ram, S.J. Image Processing with ImageJ. Biophotonics International, volume 11, issue 7, pp. 36-42, 2004.
* Niethammer, Kenneth R. and Laura B. Patrick. (1998). White Tern (Gygis alba), The Birds of North America (P. G. Rodewald, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/whiterDOI: 10.2173/bna.371
*VanderWerf, Eric A. September 2003. Distribution, Abundance, and Breeding Biology of White Terns on Oahu, Hawaii. The Wilson Bulletin, 115(3), 258-262.