While neither of those measurements provided an extremely high probability of correctly identifying the sex of the bird, the combination of the two emerged as a powerful predictor. The analysis showed that the two strongest predictors were the mass of the bird and the wing length. Measurements were taken on the weight (mass), hallux length (the longest talon), culmen length (upper bill), tarsus width (lower portion of the leg), and the wing length of each bird sampled. Using statistical analyses, scientists compared the data from the molecular work conducted in the laboratory with data collected from measurements taken from each of the hawks. Collectively, these two unique avian features meant that scientists would not only have plenty of DNA from which to work with, but would also have a set of chromosomes that could be used to clearly identify the sex of the bird. In birds, the red blood cells do carry a nucleus. In humans, the red blood cells do not have a nucleus, and therefore, they do not contain any DNA. The other major difference occurs within the red blood cells. In birds, that pattern is reversed, and it is the female that carries two different sex chromosomes, identified as W and Z, while male birds carry two Z chromosomes. In humans, it is the female that carries two "X" chromosomes (XX) while the male carries one "X" and one "Y" (XY). The first feature exists in the sex chromosomes. (Image credit: James Hewlett, Finger Lakes Community College)īirds have two genetic features that helped facilitate that part of the study. The two dark bands inside the box indicate that this data is for a female red-tailed hawk. Results of the genetic analysis conducted by Finger Lakes Community College and Braddock Bay Raptor Research (BBRR). Those samples were brought back to the research laboratories where students extracted DNA from blood, and then used a method called polymerase chain reaction to amplify a portion of the DNA that would help the scientists determine if the bird was male or female. The study would not only help banders fill in their missing data, but it would also help uncover any sex-biased dispersal and migration patterns that may exist in the red-tailed hawk population.įor five years, scientists and students from the three institutions worked with banders from BBRR to collect a small blood sample from birds that were trapped during the annual banding program. In 2005, scientists and students at Finger Lakes Community College, Rochester Institute of Technology and Delaware Technical and Community College embarked on a collaborative project with BBRR with the goal of discovering a physical characteristic that researchers could use to quickly determine the sex of a juvenile red-tailed hawk in the field. In years prior, banders would simply have to enter "unknown" in the records that they submitted to the Federal Banding Laboratory. In order to better understand if this species of hawk exhibits a sex-biased dispersal during migration, the first step would be to develop a method for determining the sex of the bird. Juvenile red-tailed hawks appear to be physically identical, regardless of their sex. The question arose because of a unique feature found in the juveniles of the species. Researchers began to question if the migration pattern existed specifically in the red-tailed hawk population. Multiple hypotheses have been put forth to explain the sex-biased dispersal pattern, but one common feature is that males and females of a given species of hawk are often physically very different - a feature referred to as sexual dimorphism - with females often being much larger. Through their activity, BBRR banders were able to observe a common pattern that has been seen in many hawk populations: the timing and distance of the migration can vary dramatically for males and females of the same species of hawk. The BBRR program maintains a network of blinds in which licensed professionals trap hawks with the purpose of installing a small metal band that contains a number issued by the Federal Bird Banding Laboratory in Maryland. (Image credit: James Hewlett, Finger Lakes Community College) An example of one of Braddock Bay Raptor Research (BBRR)'s blinds that researchers use to study hawk populations in upstate New York.
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