https://cpw.cvlcollections.org/files/original/7185c15310bfce2f80a01484617272d8.pdf 55489c5c4ec0c1616206bd131ddcdf8c PDF Text Text The research in this publication was partially or fully funded by Colorado Parks and Wildlife. Dan Prenzlow, Director, Colorado Parks and Wildlife • Parks and Wildlife Commission: Marvin McDaniel, Chair • Carrie Besnette Hauser, Vice-Chair Marie Haskett, Secretary • Taishya Adams • Betsy Blecha • Charles Garcia • Dallas May • Duke Phillips, IV • Luke B. Schafer • James Jay Tutchton • Eden Vardy �Survivorship and Mortality Patterns of Double-Crested Cormorants at Spider Island, Wisconsin, 1988–2006 Authors: Stromborg, Kenneth L., Ivan, Jacob S., Netto, John K., and Courtney, Chad R. Source: Waterbirds, 35(sp1) : 31-39 Published By: The Waterbird Society URL: https://doi.org/10.1675/063.035.sp105 BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Complete website, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/terms-of-use. Usage of BioOne Complete content is strictly limited to personal, educational, and non - commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. Downloaded From: https://bioone.org/journals/Waterbirds on 21 Oct 2021 Terms of Use: https://bioone.org/terms-of-use Access provided by Colorado Parks and Wildlife �Survivorship and Mortality Patterns of Double-crested Cormorants at Spider Island, Wisconsin, 1988-2006 Kenneth L. Stromborg1,2,*, Jacob S. Ivan3, John K. Netto4 and Chad R. Courtney5 U.S. Fish and Wildlife Service, New Franken, WI, 54229, USA 1 Present address: 5059 Larsenville Road, Denmark, WI, 54208, USA 2 Present address: Colorado Parks and Wildlife, Ft. Collins, CO, 80526, USA 3 Present address: U.S. Fish and Wildlife Service, Stockton, CA, 95205, USA 4 Present address: 8770 S. Chase, Pulaski, WI, 54162, USA 5 *Corresponding author; E-mail: kstromborg@theglobalnet.net Abstract.—Banding records were examined to identify changes in mortality causes and locations of Doublecrested Cormorants (Phalacrocorax auritus) in Door County, Wisconsin. In 14 out of 18 years between 1988 and 2005, a total of 22,469 birds were banded (300 to 5,462; average 1,605 per active banding year). Of 649 usable band returns (36.1 ± 5.4 per year), 33% were banding-year recoveries (before 1 May of the first year of life). The yearly rate of banding-year recoveries increased from 0.7% per year before 1996 to 2.2% per year after 1999. The yearly proportion of all band recoveries attributed to animal damage control operations also increased over time. The yearly proportion of band returns from Mississippi Delta states increased over time. Mortality rates, both natural and anthropogenic, of cormorants from these colonies appear to have risen as the population has grown and control activities in southern states have increased. Apparent survival rates were estimated by mark-recapture methods during 2001 to 2006. Birds color-banded as adults had a model-averaged annual survival rate of 0.696. For birds banded as nestlings, the model-averaged survival rates were: 0.305 (first year), 0.774 (second and third year), and 0.633 (adults). Simulations of these measured survival rates combined with previously estimated reproductive rates demonstrated that emigration and immigration rates complicate interpretation of these results. Also, simulations demonstrate the potential efficacy of reproductive controls in reducing local breeding populations. Submitted 21 September 2007, accepted 27 November 2009. Key words.—bird banding, Double-crested Cormorant, Lake Michigan, mark-recapture, mortality, survival. Waterbirds 35(Special Publication 1): 31-39, 2012 developing scientifically grounded management plans has proven difficult because the demographic information needed is sparse for this species (Erwin 1995). The paucity of data is related to the difficulties of capturing and handling adults and the risk of causing nest destruction and loss of young and eggs by predators when working within breeding colonies (Nisbet 1995). Using the limited data available, Blackwell et al. (2002) developed explicit population models for cormorants in order to examine the relative importance of changes in reproductive and survivorship parameters in determining population trajectories. They concluded that the most influential parameter was age-specific survivorship. Survival has rarely been reported for North American cormorants. Hickey (1952) examined literature accounts and developed a life table for this species that indicated adult survivorship The population of Double-crested Cormorants (Phalacrocorax auritus; hereafter cormorants) in the Great Lakes has increased dramatically during the decades following restrictions on use of chlorinated hydrocarbons (Weseloh et al. 1995; Wires et al. 2001). The species is an efficient fish predator, which has created conflicts with human uses of fisheries resources both in the Great Lakes region and in wintering areas in the south. Also, these birds have caused destruction of vegetation in areas where they congregate for breeding and roosting (Shieldcastle and Martin 1995). Some of those areas contain valuable patches of rare plant communities, particularly in the Great Lakes (Hebert et al. 2005). The perceived negative characteristics of cormorant populations have led to efforts to develop management plans within an overall conservation strategy within the U.S. (USDI 2003a; USDI 2003b). However, 31 Downloaded From: https://bioone.org/journals/Waterbirds on 21 Oct 2021 Terms of Use: https://bioone.org/terms-of-use Access provided by Colorado Parks and Wildlife �32 Waterbirds of 76-78% and estimated survival of the first year of 25-32% and 61-70% for the second year. Van der Veen (1973) (as reported by Hatch and Weseloh 1999) estimated much higher rates: 85% adult survivorship, 74% second year, and 48% first year at a single colony in British Columbia. The current study was initiated in 1988 during studies of the effects of environmental contaminants on cormorant reproduction (Larson et al. 1996). Nests were monitored weekly during 1988 to 1990, and nestling losses generally happened prior to 15 days after hatching. Nestlings were banded when they were older than 15 days and were expected to survive and enter the free-flying population. Post-breeding season searches produced very few dead nestlings or bands, and those records were removed from the database of banded birds. When interest in managing the Great Lakes cormorant population increased in the late 1990s, we realized that our initial banding efforts were unlikely to produce data of sufficient precision to be useful in adaptive management of this species, even on the local level. In 2001, we began to supplement traditional banding techniques based on reports of dead birds with modern markrecapture techniques for studying living birds. The primary objective of these studies was to develop a baseline measurement of adult survivorship of cormorants in the Wisconsin waters of Green Bay and adjacent Lake Michigan before major population management efforts began in that area. In 1998, the U.S. Fish and Wildlife Service issued an Aquaculture Depredation Order (USDI 1998) which permitted increased killing of cormorants around southern aquaculture facilities. The objective of the study was to determine whether increased control measures such as that outside the breeding area might be influencing the birds on our breeding colonies. Methods Cormorants were banded on six islands (Fig. 1) in 14 of 18 years from 1988 to 2005 with standard North American Bird Banding Laboratory (BBL) aluminum butt-end leg bands (Table 1). From 1988 through 1993, size 7B Figure 1. Green Bay and adjacent Lake Michigan, Wisconsin, islands where cormorants were banded between 1988 and 2005. was used, and thereafter, size 8 was used because we were informed that the smaller bands were too small to accommodate a fully grown adult tarsus (Tommy King, USDA, pers. comm.). Beginning in 2001, colored, numbered plastic leg bands (Pro-touch Engraving, Saskatoon, SK) were also applied to a subset of Spider Island birds banded with aluminum bands. Banding was done at night at Spider Island and during daylight at other sites. Nestling birds were banded while still at or near their nests at approximately 15 to 25 days of age. Adults were captured by hand or with hand-held hoop nets. Leather gauntlets were worn when handling adults and a second person was required to apply the bands to these larger birds. Banded birds were released as close to the site of capture as practical. Colonies were visited for banding from one to eight times per year, no more often than weekly. Encounter records were obtained from the BBL for aluminum bands reported through the North American Bird Banding Program. Beginning in 2002, live encounter observations were obtained at Spider Island by using spotting scopes to read the codes on the plastic leg bands. These observations were made by observers concealed in elevated blinds on the margins of subgroups within the colony. Because Herring Gull (Larus argentatus) predation on unattended nests and nestlings at the Spider Island colony was a concern, attempts were made to enter the blinds before dawn and leave prior to dusk when adults were attending to nests and had ceased leaving the colony to feed. A minimum of two and as many as four blinds were used simultaneously in order to view as much of the colony as possible. Colonies were visited no more frequently than weekly, and, after unacceptable nest losses were observed early in the 2003 nesting season, observations were delayed until after the majority of the eggs began to hatch and adults became more tenacious in nest defense. Downloaded From: https://bioone.org/journals/Waterbirds on 21 Oct 2021 Terms of Use: https://bioone.org/terms-of-use Access provided by Colorado Parks and Wildlife �Survivorship and Mortality 33 Table 1. Number and type of bands applied to nestling and adult cormorants on Green Bay and adjacent Lake Michigan, Wisconsin islands, 1988 to 2005. Ad: adults banded with aluminum butt-end bands only; N: nestlings banded with aluminum butt-end bands only; Ad-C: adults banded with aluminum butt-end band and numbered color band; N-C: nestlings banded with aluminum butt-end band and numbered color band. Location Year Spider Jack Hat 1988 24 Ad 1,527 N 16 N 36 N Gravel Fish 54 N 2N Cat Bands by age class Total bands 24 Ad 1,635 N 1,659 1989 1990 1992 1 Ad 1,657 N 19 N 26 N 8 Ad 2,362 N 75 N 5N 8 Ad 2,442 N 11 Ad 5,054 N 75 N 322 N 11 Ad 5,451 N 98 N 62 N 300 N 91 N 1993 1994 1995 1996 686 N 916 N 2,999 N 300 N 2000 85 Ad 1,407 N 1 Ad 1,757 N 55 N 174 N 184 N 28 N 922 N 1,400 N 3,216 N 300 N 922 1,400 3,216 300 85 Ad 1,407 N 1,492 2001 101 Ad-C 382 N-C 985 N 101 Ad-C 382 N -C 985 N 2002 95 Ad-C 384 N-C 95 Ad-C 384 N-C 2003 397 N-C 639 N 397 N-C 659 N 1,468 479 2004 2005 20 N 395 N-C 392 N-C 20 N 395 N-C 392 N-C 20 N TOTAL Encounter records from the BBL were initially filtered to remove local recoveries prior to migration. Several instances of significant mortality of young-of-theyear birds occurred at a nearby power plant in 1990 and 1992. These recoveries were from an enclosed cooling water system inside the plant and presumably included virtually all birds killed at this facility. These were such unusual events in terms of both scope and cause that they likely would have seriously biased the analysis had they been included. The cause of mortality was subsequently corrected, and no similar instances have occurred since nor have we been able to find any similar reports of cormorant mass mortality at any other industrial water intake in the United States. Several instances of Newcastle disease also were detected in Green Bay, 1,056 395 412 22,469 resulting in minor losses of young that were associated with natal colonies (Glaser et al. 1999). Both banding and recovery data from these mortality causes were removed to prevent inflating the number of banded birds recruited to the population. Remaining records were summarized by year for analysis of banding-year (prior to 1 May of the year following banding) and total recoveries. Wilcoxon’s two-sample test was used on the rank order of banding-year recovery rates to determine whether these rates changed after the Aquaculture Depredation Order became effective during the lapse in banding from 1997 to 1999 (Table 1). We tested for time trends in the proportion of bands applied that were reported during the first year after banding, the proportion of band recoveries related to control opera- Downloaded From: https://bioone.org/journals/Waterbirds on 21 Oct 2021 Terms of Use: https://bioone.org/terms-of-use Access provided by Colorado Parks and Wildlife �34 Waterbirds tions, and the proportion of band recoveries from the aquacultural states of the Mississippi Delta (Alabama, Arkansas, Louisiana, Mississippi) using product-moment correlations. The CJS features of the program MARK were used to determine survival and sighting probabilities of cormorants captured and marked as adults and separately, of those marked as nestlings (White and Burnham 1999). The capture of adults was quite disruptive to the entire colony compared to our long-standing practice of banding nestlings, and this difference could well be reflected in estimates of adult survival rates derived from the two groups of marked birds. In addition, assigning an age to the birds marked as adults was not possible, whereas the ages of those banded as nestlings were known. Sighting histories were compiled for each bird by year in order to construct models of survivorship and sighting probabilities. Adult data were not overdispersed and are reported as Akaike’s information criterion corrected for small sample size (AICc). A priori models of survival and sighting probabilities were constructed for birds marked as adults based on potential variation or constancy between calendar years (time), and also on potential temporary variation caused by capture (Table 2). We hypothesized that in response to capture and handling, in the year following marking, birds might temporarily leave the Spider Island colony or change their location or visibility relative to the observation blinds and that this would be reflected in different sighting probabilities between the 2001 and 2002 cohorts in the 2003 observation sessions. In addition, if marking caused birds to permanently leave Spider Island, this would be reflected in a difference between the two cohorts in the 2002 survival probabilities. Other differences between the adults captured in 2001 and 2002 were not modeled because we believe these were samples drawn from the pool of available adults and that there was no reason to expect any differences between these samples. Models for birds banded as nestlings were similar except that it was possible to recognize age classes. The issue of age classes introduced complexity to these models because the age at which cormorants become full adults and enter the breeding population is not known, nor is it likely to be uniform among individuals (Hatch and Weseloh 1999). Age classes were identified as first year, second year (yearlings), third year (sub-adults), or second and third year combined (juveniles), and adults defined either as including all third year and older, or fourth year and older birds (Table 2). The number of models constructed was limited, because different amounts of effort and observation points were used to identify marked birds in each year and sighting probabilities would be different between years based on these differences and possibly other unidentified factors. Thirteen models of potential interest were tested based on constant or time-varying sighting and survival probabilities (Table 3). As data were over-dispersed, the median c-hat procedures within MARK were used to correct for this. Akaike’s information criterion corrected for small sample size and overdispersion (QAICc ) is reported for birds banded as nestlings. Estimated survival and sighting probabilities were averaged across models using the AICc weights for birds banded as adults and the QAICc weights for birds banded as nestlings. Estimated survival rates were used to construct simple population models in order to examine the potential effects of reproductive controls on the population trajectory of the Spider Island colony. Age-specific survival rates were used for birds banded as nestlings, and also the survival rate for birds banded as adults was combined with survival rates for the younger age classes estimated from birds banded as nestlings. The average reproductive rate estimated for this colony in previous years (Larson et al. 1996; Custer et al. 1999) was used. Ten generations of survival and reproduction were simulated to reach a stable age distribution for each combination of survival and reproductive rates in order to determine the yearly change in the total population. Also, we were interested in determining the proportion of the total population that was participating in reproduction because censuses are based on nest counts, whereas the total population is of interest when estimating potential consumption of fish over a geographic location. The total population is usually estimated by expanding the number of breeding adults to account for Table 2. Notation used to identify Φ (survival) and p (sighting) parameters in models of visual encounter records of cormorants marked as adults or nestlings at Spider Island, Wisconsin, 2001 to 2005. Age at marking (years of marking) Parameter variability between years Adults (2001, 2002) (•) = constant (t) = variable between years (handling) = 2001 birds different from 2002 birds during 2002-2003 Nestlings (2001-2005) (•) = constant (t) = variable between years (n) = first-year birds (y) = second-year birds (s-a) = third-year birds (juv) = second- and third-year birds combined (ad) = adults Downloaded From: https://bioone.org/journals/Waterbirds on 21 Oct 2021 Terms of Use: https://bioone.org/terms-of-use Access provided by Colorado Parks and Wildlife �Survivorship and Mortality 35 Table 3. Model selection criteria for survivorship related to years and age for cormorants banded as nestlings at Spider Island, Wisconsin, 2001 to 2005. Delta QAICc: change in Akaike’s information criterion adjusted for small sample size and overdispersion. Key to notation is shown in Table 2. Model Φ(n-t,juv-t,ad-t), p(n-t,juv-t,ad-t) Φ(n-t,y-t,ad-t), p(n-t,y-t,ad-t) Φ(n-t,y-t,sa-t,ad-t), p(n-t,y-t,sa-t,ad-t) Φ(n-t,y-t,ad-t), p(n,y,ad) Φ(sat1), p(sat) Φ(n-t,y-t,ad-t), p(t) Φ(n-t,y-t,ad-t), p(t) Φ(n,y,ad), p(t) Φ(n,ad), p(t) Φ(n,y,ad), p(•) Φ(n,ad), p(•) Φ(t), p(t) Φ(•), p(•) Delta QAICc QAICc weight Number of parameters QDeviance 0.00 1.71 5.03 5.05 9.09 14.26 14.65 14.80 17.17 57.43 67.38 124.87 180.08 0.625 0.266 0.050 0.050 0.007 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 21 23 27 15 29 16 16 8 7 4 3 9 2 42.117 39.745 34.887 59.366 34.839 66.548 66.941 83.262 87.644 133.939 145.899 191.315 260.603 (sat) = survivorship and sighting probabilities for all time and age parameter combinations different. 1 younger non-breeders. The cases of all third year and older breeding and only half of the third year plus all of the fourth year and older breeding were examined. Finally, each of the preceding scenarios was simulated with an assumed 90% reduction in reproduction such as might be achieved with an egg-oiling program. Results In total, 22,469 cormorants were banded in 14 out of 18 years from 1988 to 2005 (1605 ± 370 per active banding year). Adjusting encounter records for these birds based on known local, catastrophic recoveries yielded 649 available bands (36.1 ± 5.4 per year). Of these, 33% were banding-year recoveries. The rate of banding-year recovery increased from an average of 0.7% per year before 1997 to 2.2% per year after 1999 (t12 = 3.817, P = 0.0025; Fig. 2). The proportion of recoveries (both banding-year and later) that could be ascribed to animal damage control activities increased over time (r16 = 0.824, P ≤ 0.0001; Fig. 3). The proportion of recoveries from the aquacultural states of the Mississippi Delta also increased over time (r16 = 0.757, P = 0.0003; Fig. 3). Analysis of a priori models describing constant or yearly (2001-2005) variable survival and resighting probabilities indicated that the adult data were best fit by a model with a constant survival rate across years and a resighting rate that varied by year (Table 4). A model with yearly variability in both survival and re- Figure 2. Proportion of bands recovered prior to May of the first year after banding (banding-year recoveries) of cormorants in Green Bay and adjacent Lake Michigan, Wisconsin. sighting probabilities was also well supported by the data. Some support was found in the data for models that incorporated differences between the two adult cohorts in the year following banding. The effect was relatively well supported for resighting rates, and there was weaker support for an effect on survival probability. For birds banded as adults, the modelaveraged survival rate was 0.696 and the sighting probability was 0.580 (Table 5). Analysis of data for birds banded as nestlings introduced a number of potential new parameters related to age classes. The model best supported by the data grouped birds in Downloaded From: https://bioone.org/journals/Waterbirds on 21 Oct 2021 Terms of Use: https://bioone.org/terms-of-use Access provided by Colorado Parks and Wildlife �36 Waterbirds vival and resighting probabilities and first year, second year and adult age classes with yearly variable survival rates and average age-specific sighting rates. Model-averaged survival rates were 0.305 for first year, 0.774 for second and third year, and 0.633 for fourth year and older birds. Resighting probabilities averaged 0.205 for first-year birds, 0.552 for second-year birds, and 0.583 for adults (Table 5). Discussion Figure 3. Proportion of band recoveries attributed to control activities and proportion of band recoveries from Mississippi Delta states (Alabama, Arkansas, Louisiana, Mississippi) of cormorants banded at Green Bay and adjacent Lake Michigan colonies, 1988 to 2005. the second and third years of life and recognized variability between years in survival and resighting rates (Table 3). Another model well supported by the data grouped birds into the first year of life, the second year of life, and combined the third and later years of life with both survival and resighting probabilities varying over years. Two models had some support from the data: four age categories, first, second, third, and all subsequent years of life with variability between calendar years in both sur- Figure 4. Nest count censuses of Green Bay and adjacent Lake Michigan, Wisconsin, cormorant populations, 1997 to 2005 (adapted from Wires et al. 2001 and Weseloh et al. 2006). One of the primary reasons for estimating age-specific survival rates of cormorants at northeastern Wisconsin island colonies is to develop an adaptive management strategy for this population. From almost two decades of banding and analysis of ordinary encounter data from the BBL, we determined that apparent mortality rates had increased, at least for birds in the first year of life. This could be attributed to either increasing amounts of control activity on the wintering grounds, and more recently in the general area of the Great Lakes, or it might be an artifact of better reporting of bands by agents carrying out control. Our data cannot answer the causal question. Most likely, a combination of these two factors is the explanation for the increased rate of bandingyear returns of BBL bands in recent years. An adaptive management strategy has to focus on whether control efforts are achieving a desired result. Blackwell et al. (2002) modeled hypothetical cormorant population trajectories using the best estimates available at the time. The present study was designed to add targeted survivorship information to this process. Our results are focused on a single colony but they do represent an intensive study of mortality rates during years without local control activities and could be applicable to a broader context. All of the population trajectories for this population were decreasing at 4 to 8% per year (Table 6). The population was composed of 68 to 76% breeders. Such composition means that estimates of the total population used to project fish consumption by adults should be increased 33 to 50% above nest counts to account for non-breeding, fully grown birds. Downloaded From: https://bioone.org/journals/Waterbirds on 21 Oct 2021 Terms of Use: https://bioone.org/terms-of-use Access provided by Colorado Parks and Wildlife �Survivorship and Mortality 37 Table 4. Model selection criteria for survivorship related to year of banding and potential handling effects of cormorants banded as adults in 2001 and 2002 at Spider Island, Wisconsin. Delta AICc: change in Akaike’s information criterion adjusted for small sample size. Key to notation is shown in Table 2. Model Delta AICc Model weight Φ(•), p(t) Φ(t), p(t) Φ (t), p(t-handling) Φ (t-handling), p(t-handling) Φ (t), p(•) Φ (•), p(•) 0.00 0.70 2.22 3.96 7.94 18.06 0.457 0.321 0.150 0.063 0.009 0.000 Number of parameters 7 11 12 13 7 2 Deviance 70.441 62.735 62.124 61.725 78.378 98.761 Table 5. Model averaged (over time) survival (Φ) and sighting (p) probabilities of cormorants color marked as adults or nestlings at Spider Island, Wisconsin, 2001 to 2005. Age at marking Age class Adult Nestling Nestling Nestling Adult (at least two years) First year Second and third year Adult (at least four years) Survival (Φ) Sighting (p) 0.696 0.305 0.774 0.633 0.580 0.205 0.552 0.583 Table 6. Calculated changes in population size and composition related to adult survival rate, age of first breeding, and reproductive control. Adult survival Third-year breeding Egg oiling Yearly % population change Percent breeders High1 High3 Low4 No No -3.8 -6.3 76 68 Low2 High Low No No -5.7 -8.3 76 68 High High Low Yes Yes -26.8 -26.9 96 94 Low High Low Yes Yes -29.8 -29.9 96 94 Adult survival estimated from birds marked as adults. Adult survival estimated from birds marked as nestlings. All birds breed beginning in the third year of life. 4 Half of third year birds breed, all fourth year and older breed. 1 2 3 The actual population trajectory at Spider Island was increasing until 1998. The trajectory then decreased between 1998 and 2002 and remained relatively constant at the last census in 2005 (Wires et al. 2001; C. Weseloh unpublished data). The overall population of Green Bay cormorants was continuing to grow during this entire period (Fig. 4). Because the survival rates reported here are apparent survival rates, emigration of color-banded birds can bias estimates downward. The disturbance of our intensive observations may have had such an effect, particularly during 2003 when observation visits were made early in the nesting season. Program limitations precluded comprehensive surveys for emigrants even at a scale including nearby Wisconsin colonies. The possibility of lowered apparent survival rates, as a result of observer-induced disturbance has been identified in other studies as a needed focus of further study (Duerr et al. 2007). When a 90% reproductive control was imposed on these simulated populations, they decreased at 27-30% per year (Table 6). A secondary effect of reproductive control measures may be an increase in emigration from colonies subject to control. Increased emigration would lower apparent, but perhaps not actual, survival of older age Downloaded From: https://bioone.org/journals/Waterbirds on 21 Oct 2021 Terms of Use: https://bioone.org/terms-of-use Access provided by Colorado Parks and Wildlife �38 Waterbirds classes. Focusing control programs on reproduction should also mitigate concerns about humane issues arising from shooting breeding adults that have dependent young. Finally, the population structure of these reproductively-controlled populations was dominated by adult breeders (approximately 95%). In such populations, little correction to nest census data would be needed to account for fish consumption by non-breeders and consumption by growing young would be a minimal contribution to total fish consumption by the local cormorant population. We believe these simulations demonstrate the power of reproductive control to influence local cormorant populations rapidly by restricting recruitment to the population. Acknowledgments The research was conducted under U.S. Federal Bird Banding permit #22281. We appreciate the cooperation of private landowners in granting access to Hat and Jack Islands. We thank J. Hemming and K. Hansen for assistance with the manuscript and an anonymous reviewer who led us to explore additional analyses. Funding was provided by the Environmental Contaminants and Migratory Birds programs of the U.S. Fish and Wildlife Service, but the conclusions and opinions expressed are those of the authors. Finally, we are grateful for the efforts of the many volunteers who assisted over the years both in banding and recording observations under often uncomfortable and demanding conditions. Literature Cited Blackwell, B. F., M. A. Stapanian and D. V. C. Weseloh. 2002. Dynamics of the Double-crested Cormorant population on Lake Ontario. Wildlife Society Bulletin 30: 345-353. Custer, T. W., C. M. Custer, R. K. Hines, S. Gutreuter, K. L. Stromborg, P. D. Allen and M. J. 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Colonial waterbird nesting on West Sister Island National Wildlife Refuge and the arrival of Double-crested Cormorants. Pages 115-119 in Symposium on Double-crested Cormorants: Population Status and Management Issues in the Midwest. USDA APHIS Technical Bulletin No. 1879 (Mark E. Tobin, Tech. Coord.). U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Washington, D.C. USDI (U.S. Department of the Interior) 1998. Migratory bird permits: Establishment of a depredation order for the Double-crested Cormorant. Federal Register 63: 10550-10561. USDI. 2003a. Migratory bird permits: Regulations for Double-crested Cormorant management. Federal Register 68: 58022-58037. USDI. 2003b. Final Environmental Impact Statement: Double-crested Cormorant Management in the United States. U.S. Department of the Interior, Washington, D.C. van der Veen, H. E. 1973. Some aspects of the breeding biology and demography of the Doublecrested Cormorants (Phalacrocorax auritus) of Mandarte Island. Unpublished Ph.D. Thesis, Riksuniversiteit te Groningen, Groningen, Holland. Weseloh, D. V., P. J. Ewins, J. Struger, P. Mineau, C. A. Bishop, S. Postupalsky and J. P. Ludwig. 1995. Double-crested Cormorants of the Great Lakes: Changes in population size, breeding distribution and reproductive output between 1913 and 1991. Colonial Waterbirds 18 (Special Publication): 48-59. Downloaded From: https://bioone.org/journals/Waterbirds on 21 Oct 2021 Terms of Use: https://bioone.org/terms-of-use Access provided by Colorado Parks and Wildlife �Survivorship and Mortality White, G. C. and K. P. Burnham. 1999. Program MARK: Survival estimation from populations of marked animals. Bird Study 46 (Supplement): 120-138. Wires, L. R., F. J. Cuthbert, D. R. Trexel and A. R. Joshi. 2001. Status of the Double-crested Cormo- 39 rant (Phalacrocorax auritus) in North America. Final Report to U.S. Fish and Wildlife Service. University of Minnesota, St. Paul, Minnesota. Accessed at: http://www.fws.gov/migratorybirds/ CurrentBirdIssues/Management/cormorant/ cormorant.html. Downloaded From: https://bioone.org/journals/Waterbirds on 21 Oct 2021 Terms of Use: https://bioone.org/terms-of-use Access provided by Colorado Parks and Wildlife � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Journal Articles Description An account of the resource CPW peer-reviewed journal publications Text A resource consisting primarily of words for reading. Examples include books, letters, dissertations, poems, newspapers, articles, archives of mailing lists. Note that facsimiles or images of texts are still of the genre Text. Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Survivorship and mortality patterns of double-crested cormorants at Spider Island, Wisconsin, 1988–2006 Description An account of the resource <span>Banding records were examined to identify changes in mortality causes and locations of Double-crested Cormorants (</span><i>Phalacrocorax auritus</i><span>) in Door County, Wisconsin. In 14 out of 18 years between 1988 and 2005, a total of 22,469 birds were banded (300 to 5,462; average 1,605 per active banding year). Of 649 usable band returns (36.1 ± 5.4 per year), 33% were banding-year recoveries (before 1 May of the first year of life). The yearly rate of banding-year recoveries increased from 0.7% per year before 1996 to 2.2% per year after 1999. The yearly proportion of all band recoveries attributed to animal damage control operations also increased over time. The yearly proportion of band returns from Mississippi Delta states increased over time. Mortality rates, both natural and anthropogenic, of cormorants from these colonies appear to have risen as the population has grown and control activities in southern states have increased. Apparent survival rates were estimated by mark-recapture methods during 2001 to 2006. Birds color-banded as adults had a model-averaged annual survival rate of 0.696. For birds banded as nestlings, the model-averaged survival rates were: 0.305 (first year), 0.774 (second and third year), and 0.633 (adults). Simulations of these measured survival rates combined with previously estimated reproductive rates demonstrated that emigration and immigration rates complicate interpretation of these results. Also, simulations demonstrate the potential efficacy of reproductive controls in reducing local breeding populations.</span> Bibliographic Citation A bibliographic reference for the resource. Recommended practice is to include sufficient bibliographic detail to identify the resource as unambiguously as possible. Stromborg, K. L., J. S. Ivan, J. K. Netto, and C. R. Courtney. 2012. Survivorship and mortality patterns of double-crested cormorants at Spider Island, Wisconsin, 1988–2006. Waterbirds 35:31–39. <a href="https://doi.org/10.1675/063.035.sp105" target="_blank" rel="noreferrer noopener">https://doi.org/10.1675/063.035.sp105</a> Creator An entity primarily responsible for making the resource Stromborg, Kenneth L. Ivan, Jacob S. Netto, John K. Courtney, Chad R. Subject The topic of the resource Bird banding Double-crested Cormorant Lake Michigan Mark-recapture Mortality Survival Extent The size or duration of the resource. 10 pages Date Created Date of creation of the resource. 2012-12-01 Rights Information about rights held in and over the resource <a href="http://rightsstatements.org/vocab/InC-NC/1.0/" target="_blank" rel="noreferrer noopener">In Copyright - Non-Commercial Use Permitted</a> Format The file format, physical medium, or dimensions of the resource application/pdf Language A language of the resource English Is Part Of A related resource in which the described resource is physically or logically included. Waterbirds Type The nature or genre of the resource Article