Geology topics

Darrell L. Whitworth

Publications and source records attributed to Darrell L. Whitworth.

5 recordsLinked to original sources

USGS2016

Occurrence, morphometrics, and plumage variability among Leach’s Storm-Petrels Oceanodroma leucorhoa in the California Channel Islands, 1976–2015

We mist-netted and examined Leach’s Storm-Petrels Oceanodroma leucorhoa (LESP) caught during 1991–2015 at three locations in the California Channel Islands (CCI): Prince Island, Santa Barbara-Sutil islands and Scorpion Rock. Although mist-netting methods and effort varied between two study periods (1991–1995, 2004–2007 and 2015), during 750 h effort we captured 41 LESP during April–August, with two of these recaptured after initial banding. The majority (78%) were classified as likely breeders based on a well-developed incubation patch. We summarize island-specific efforts, capture rates and morphological measurements made at these three CCI locations. Captured LESP displayed a multimodal distribution in the overall degree of white rump plumage, with 28% classified as mostly “dark-rumped.” The majority of LESP (72%) captured in the CCI have variable white rumps, similar to what has been reported for northern California and the Farallon Islands. However, the relative proportions of “dark-rumped” individuals captured in the northern CCI is intermediate, within the shift starting at the Farallon Islands and increasing in prevalence toward the San Benito Islands, Baja California. More remains to be learned about LESP in the CCI, for which additional mist-netting efforts are needed, using a standardized approach that targets LESP.

California↗

USGS2008

Distribution of Xantus' Murrelet Synthliboramphus hypoleucus at sea in the Southern California Bight, 1995-97

We radiomarked 153 Xantus' Murrelets Synthliboramphus hypoleucus captured at sea near Santa Barbara Island (SBI), the largest murrelet colony in the California Channel Islands, USA. We tracked these radiomarked murrelets in the Southern California Bight (SCB) off coastal southern California during the 1995-97 breeding seasons. In 1995 during mild El Niño conditions, the murrelets were distributed in non-upwelling areas. In 1996-97, they were distributed in dense patches, aggregating in cool upwelled waters near the northern Channel Islands or south of San Nicolas Island. Murrelets flew longer distances from SBI to foraging areas in 1997 (x̄= 111 ± 44 km) than in 1996 (x̄= 62 ± 25 km), but the distances they travelled did not differ between months (Apr and May) within years. Mean foraging distances from SBI were similar for ‘incubating’ murrelets (determined on the basis of repeated visits to SBI) and ‘non-incubating’ murrelets during the colony attendance period. We attributed the low return rate of radiomarked murrelets to SBI to the capture and marking of a large proportion of birds that were not actively incubating rather than to any adverse effects of radio attachment. We believe changes in murrelet foraging patterns between the 1970s and 1990s are associated with changes in prey resources in the SCB. Flexibility in the foraging strategies of these murrelets may be related to the highly variable marine environment at the southern end of the California Current Up welling System.

California↗

USGS2004

Effects of radiotransmitters on the reproductive performance of Cassin's auklets

We examined whether radiotransmitters adversely affected the reproductive performance of Cassin's auklets ( Ptychoramphus aleuticus ) breeding on the California Channel Islands during 1999-2001. We attached external radiotransmitters to 1 partner in 108 Cassin's auklet pairs after nest initiation and used 131 unmarked, but handled, pairs as controls. Compared to alpha chicks raised by radiomarked pairs, alpha chicks raised by unmarked pairs had faster mass growth rates (1.95 ± 0.30 g d −1 vs. 3.37 ± 0.53 g d −1 , respectively), faster wing growth rates (2.46 ± 0.10 mm d −1 vs. 2.85 ± 0.05 mm d −1 ), greater peak fledging masses (118.9 ± 3.5 g vs. 148.3 ± 2.4 g), and higher fledging success (61% vs. 90%). Fledging success was reduced more when we radiomarked the male (50% fledged) rather than the female partner (77% fledged). After fledging an alpha chick, unmarked pairs were more likely to initiate a second clutch (radiomarked: 7%; unmarked: 39%) but did not hatch a second egg (radiomarked: 4%; unmarked: 25%) or fledge a second (beta) chick (radiomarked: 4%; unmarked: 18%) significantly more often than radiomarked pairs. We resighted 12 radiomarked individuals nesting during a subsequent breeding season; each bird had shed its transmitter and healed the site of attachment. We suggest caution in using telemetry to evaluate the reproductive performance of alcids, but marking only females may minimize adverse effects.

California↗

USGS1999

Subcutaneous anchor attachment increases retention of radio transmitters on Xantus' and marbled murrelets

We modified a subcutaneous anchor attachment and achieved transmitter reten- tion times that exceeded those reported previously for other attachments used on alcids. Traditional suture and epoxy attachment methods were used on Xantus' Murrelets in 1995 and 1996, while the modified attachment was used for Xantus' Murrelets in 1996 and 1997 and Marbled Murrelets in 1997. Modifications included use of an inhalant anesthetic, placing the anchor in a more cranial position on the back, application of marine epoxy, and place- ment of a single subcutaneous non-absorbable suture at the caudal end of the radio to hold the radio in place initially. We located 22 of 56 (39%) Xantus' Murrelets radio-marked using suture and epoxy during aerial surveys in 1995 and 1996. Of birds radio-marked using the subcutaneous anchor attachment, we located 92 of 113 (81%) Xantus' Murrelets marked in 1996 and 1997 and all 28 (100%) Marbled Murrelets marked in 1997 during aerial surveys. The maximum confirmed duration for the subcutaneous anchor transmitter attachment was 51 d for Xantus' Murrelets and 78 d for Marbled Murrelets versus 41 d for the suture and epoxy attachment used on Xantus' Murrelets. Recapture rates of radio-marked Xantus' Mur- relets were similar to recapture rates of unmarked Xantus' Murrelets. Our post-release ob- servations indicated negligible short-term physical effects from the attachment procedure, while telemetry data and examination of recaptured murrelets indicated no evidence of infection or other long-term physical effects. Breeding behavior of some murrelets was not disrupted; however, further evaluation of potential effects of this attachment technique on breeding and behavior is needed.

Journal of Field Ornithology↗

USGS1997

A night-lighting technique for at-sea capture of Xantus' Murrelets

We captured 575 Xantus' Murrelets ( Synthliboramphus hypoleucus ) with spotlights and dip nets at 3 islands in the Southern California Channel Islands during April and May of 1995-1997. Working at night (2100-0500 h), 3-person teams in inflatable boats located murrelets with a spotlight and captured them in dip nets from the waters near known breeding colonies at Santa Barbara, Anacapa, and San Clemente Islands. Our average capture rate was 4.7 murrelets hr -1 , but we captured up to 12.3 murrelets hr -1 . We recaptured 34 murrelets or 6% of the capture total. We recommend this simple, inexpensive, safe and effective night-lighting capture technique for Xantus' Murrelets and other seabirds.

Colonial Waterbirds↗