By Bryan Watts | bdwatt@wm.edu | (757) 221-2247
March 30, 2019
With 32 occupied territories, Virginia supported the largest breeding population of peregrine falcons ever known to occupy the state during the 2018 season (download the 2018 report). Since the reintroduction of captive-reared birds in the late 1970s and the first successful breeding in 1982, the population has managed show consistent growth with an average annual rate of 8%. As far as can be determined, the historic population of peregrine falcons that nested in the mountains of Virginia supported approximately 25 breeding pairs. The modern population depends primarily on man-made structures for nesting. Only two known pairs in 2018 nested on natural cliff faces.
Despite the high number of occupied territories, 2018 was a mixed year for breeding performance. Hatching rate was relatively low (67%, 45 of 67 eggs followed). Of 17 clutches that were followed completely from hatching to fledging, 36 of 57 (63%) eggs hatched and 36 of 36 (100%) survived to banding age. Three young were known to be lost after fledging. The reproductive rate (1.25 young/occupied territory) was considerably lower than in recent years.
A contributing factor to poor breeding performance in 2018 was an unusually-high turnover in adult females (see our story about female peregrines under pressure). Thirty-five percent of known females turned over between 2017 and 2018. Exchanges often result in contests to fill open breeding slots, replacement by younger less experienced birds, and disruption in breeding. Replacement of so many females appears to have impacted performance on a population scale. We would anticipate that performance will normalize as pairs settle.
We continued dedicated efforts in 2018 to identify breeding adults via field-readable bands to better understand dispersal and demography. We determined the banding status of 46 (73%) of the 64 adult peregrines known within the breeding population. The alpha-numerics were read for 29 adults. Of the banded birds where state of origin could be determined, 22 were from Virginia, 3 were from New Jersey, 4 were from Maryland, and 1 was from Pennsylvania. The natal territories were determined for 27 adults. Breeding adults ranged in age from 3 to 18 years old.
A bald eagle nest just off the Poropotank River in Virginia in 2003. A nest with two equal young and ample food was a normal scene during this time period. This reflects a golden period during the late 1990s and early 2000s when males had more leisure time to hunt and provide for broods. Photo by Catherine Markham.
Breeding female on the Eltham Bridge. This female was hatched on Elkins Marsh along the seaside of the Delmarva in 2010 and has held the territory on the Eltham Bridge since 2013 with three successive males. She has been very aggressive and protective of the nest site and has held the territory together. She was found with a wing injury from a collision in December and could not be rehabilitated. She is one of a number of falcons that have been documented to go down in 2022. Photo by Bryan Watts.