Figure
1.
The Egyptian Vulture (Neophron percnopterus)(Photo by Hong Guo)
| Citation: |
J. Dylan Maddox. 2017: Assigning hatchlings to eggs: Is relative mass assignment an accurate method?. Avian Research, 8(1): 17. DOI: 10.1186/s40657-017-0077-2
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Accurately assigning hatchlings to the eggs from which they hatched is a prerequisite to understanding how the composition and environment of eggs affect the growth and survival of nestlings. Correctly assigning hatchlings to their eggs can be a challenging endeavor, however, because multiple eggs within the same clutch can hatch at essentially the same time. Egg and hatchling mass are highly correlated in most bird species, and thus assigning eggs to hatchlings using their relative mass (e.g., matching the heaviest hatchling to the heaviest candidate egg) could prove extremely useful.
To assess its potential utility, I applied relative mass assignment (RMA) retrospectively to a dataset of 133 Common Grackle (Quiscalus quiscula) nests in which all egg-hatchling dyads were determined unequivocally.
I found that RMA correctly assigned approximately 90% of hatchlings to their eggs when 2-4 hatchlings were present between checks. The number of nests in which hatchlings could not be assigned to their egg, however, increased monotonically from 13 to 46 to 78% for nests containing 2, 3, and 4 hatchlings, respectively, due to the greater likelihood that the mass of hatchlings or their candidate eggs was identical.
Although RMA correctly identified the vast majority of egg-hatchling dyads, researchers should use this method with caution, because it will always inflate positive egg-size effects and thus could potentially result in erroneously reporting significant effects.
In 2 April 2012 a birdwatcher, Mr. Hong Guo, found a strange white bird near a garbage dump in Wuqia County, (39°55′N, 75°15′E), at an elevation of 2100 m. This location is approximately 80 km west of Kaxgar. After experts checked the photographs, it was identified as an adult Egyptian Vulture (Neophron percnopterus), also known as the White Vulture (Fig. 1). This is the first time a Chinese bird-watcher photographed this vulture.
The point of record, Wuqia County, is about 110–130 km distance from the border of Kyrgyzstan and Tajikistan. The Egyptian Vulture is found in southwestern Europe, northern Africa, south and west Asia, as well as some countries neighboring China, i.e., India, Nepal, Pakistan, Afghanistan, Tajikistan, Kyrgyzstan and Kazakhstan. This bird likes to live in groups and use old nests. This species is genetically relatively close to the Bearded Vulture or Lammergeier (Gypaetus barbatus).
The Egyptian Vulture is a medium to large bird (length 56–64 cm); its entire body is white but its flight feathers are black, it has a small head with a narrow and long bill and a wedge-shaped tail (Fig. 2). They sometimes crack eggs by using a stone, a rare example in the case raptors of knowing how to use tools.
Actually, this was not the first record in Xinjiang. About eleven years ago in the Ili River Region (43°37′N, 82°25′E), Jesper Hornskov reported a bird watching record of this species (Hornskov, unpublished; Ma, 2001). However, it was reported as an observation but no photograph is available of the event and therefore no proof of its occurrence at the time. Apparently, this is then the first record for China for this bird (not listed by Cheng, 1987, 2000; Ma, 1995; Yan et al., 1995; MacKinnon et al., 2000; Zheng, 2011), although de Schauensee (1984) noted that "[the species] possibly occurs in W Sinkiang in the Tien Shan region." Flint et al. (1984) listed the species in Kazakhstan and mapped it as occurring right up to the Xinjiang border at about 45°N. Mr. Hong Guo took about 40 clear photos of the event, providing strong evidence of a new record for Chinese birds. It is initially identified as the subspecies Neophron percnopterus percnopterus (Fig. 2).
The program is supported by the National Natural Science Foundation of China (No. 30970340, 31272291).
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