Accuracy of Census Methods of Territorial Red-Winged Blackbirds

Francis, William J.

doi:10.2307/3799746

Cited by 3 publications

(2 citation statements)

References 7 publications

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“…The overall density was one kite/l,6 km but higher near the towns (1 kite/0,8 or 0,9km). The actual density may be higher since buildings of small villages occasionally blocked the view of potential perches and roadside censuses tend to underestimate the true population (Francis 1973). The only other species which used these perches were Laughing or Turtle Doves (Streptopelia senegalensis and S. turtur).…”

Section: Early Literature Indicates That Blackshoulderedmentioning

confidence: 99%

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Hanmer¹,

Lendrum²,

Lendrum³

et al. 1982

Ostrich

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There are many methods of calculating mortality rates in birds, but none appear to be entirely satisfactory, due to the number of possible instances of bias when dealing with living organisms. The method used here is that used by Brown & Pomeroy (In press, Proc. 5th Pan-Afr. Om. Congr. ), for their attempt to show that mortality rates are related to weight. It is a very simple method, but since the samples obtained from recaptures are very small, there is no justification for the use of a more sophisticated method.Using recapture data, the number of birds surviving each successive year after ringing is listed. Then the numbers surviving at hypothetical constant annual mortality rates are calculated, to see which rate best fits the actual figures. This method assumes that birds do not lose their rings, emigrate or otherwise escape capture and that the annual mortality rate of adults is constant. None of these are necessarily true. In their middle years, bird mortality rates do not appear to differ greatly, but without supporting evidence this remains an assumption and Fry (1980, Proc. 4th Pan-Afr. Om. Congr.: 333-343.) ~ ~~ ~ ~~ Annual Predicted survival with annual mortality mortality rate of rate (%) -----37% I 36% I 35% 1 34% I 33% TABU 1 NUMBER OF ADULT LITTLE BEE-EATERS RINGED AND RECAUGXr OVW YEARS, "HEIR ANNUAL MORTALITY RATES AND THE NUMBER W W G AT CERTAIN RYPOTHBTICAI, CONSTANT ANNUAL MORTALITY RATES. 5 6 I --suggests that some species show a decrease in mortality rate with age. One hundred and twenty-five apparently adult and 42 visibly immature Little Bee-eaters Merops pusillus were ringed between March 1974 and June 1979 at Nchalo, Mala+i (16 16s; 34 55E). Some of these were recaptured in succeeding years, up to January 1982. Years were taken from July to June.As immature Little Bee-eaters cannot be identified after they are four months old, there are probably many immatures included in the adult group. Table 1 gives the number of apparent adults ringed and recaught over seven years (none has been recaught more than seven years after being ringed). Table 2 gives the number of known immatures ringed and recaught over six years. The adult mortality rate in the first year is 76 %. This is almost certainly mainly due to immature mortality and dispersal, as the immature first-year mortality rate is similar (7479, although adults may be partly migratory, which could account for a small proportion of the loss. After the first year the percentage mortality is considerably less, so that in calculating the hypothetical annual mortality rates for comparison with the actual figures, the first year was excluded. Five hyopthetical rates were calculated (to two decimal places, but rounded off to the nearest whole bird) TABLE 2 N U M B E R OF IMMATURE LITTLE BEE-EATERS RINGED AND RECAUGHT OVER SIX YEARS, THEIR ANNUAL MORTAIXIT RATES AND THE NUMBERS SURVIVING AT CERTAIN HYPOTHETICAL CONSTANT ANNUAL MORTALITY RATES. Predicted survival with annual mortality rate of year I rate(%j -----Year I (actual)

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Section: Early Literature Indicates That Blackshoulderedmentioning

confidence: 99%

Short Notes

Hanmer¹,

Lendrum²,

Lendrum³

et al. 1982

Ostrich

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“…These studies attempted to resolve the problem of inexact identification using a combination of landmarks, vegetation cover, speed of a survey vehicle, bird behaviours, distances between locations and the removal of some observations to assign encounters as recaptures or new marks. Although Hewitt’s (1967) population estimates were consistent (Francis 1973), these solutions lacked standardization within and among surveys and may have contributed to unknown levels of bias in the resulting population estimates. Subsequently, the use of point coordinates for constructing capture–recapture encounter histories has not been widely adopted or applied to encounter histories with more than two encounter occasions.…”

Section: Introductionmentioning

confidence: 99%

Estimating population size using capture-recapture encounter histories created from point-coordinate locations of animals

Manning

Goldberg

2010

Methods in Ecology and Evolution

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Summary1. Estimating population size is a fundamental objective of many animal monitoring programmes. Capture-recapture methods are often used to estimate population size from repeated sampling of uniquely marked animals, but capturing and marking animals can be cost prohibitive and affect animal behaviours, which can bias population estimates. 2. We developed a method to construct spatially explicit capture-recapture encounter histories from locations of unmarked animals for estimating population size with conventional capturerecapture models. Prior estimates of the maximum distance individuals move in the population is used to set a summary statistic and process subsequent capture-recapture survey data. Animal locations are recorded as point coordinates during survey occasions, and the parameter of interest is abundance of individual activity centres. 3. We applied this method to data from a point-coordinate capture-recapture survey of burrowing owls Athene cunicularia in the Imperial Valley of California, USA. We also used simulations to examine the utility of this technique for additional species with variable detection probabilities, levels of home range overlap and distributions of activity centres within a survey area. 4. The estimates from empirical and simulation studies were precise and unbiased when detection probabilities were high and territorial overlap was low. 5. This method of estimating population size from point locations fills a gap in non-invasive census and long-term monitoring methods available for conspicuous species and provides accurate estimates of burrowing owl territory abundance. The method requires high detection probabilities, low levels of home range overlap and that individuals use activity centres. We believe that these requirements can be met, with suitable survey protocols, for numerous songbird and reptile species.

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Methoden der Bestandserfassung in der Ornithologie: Übersicht und kritische Betrachtung

Berthold

1976

J Ornithol

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Accuracy of Census Methods of Territorial Red-Winged Blackbirds

Cited by 3 publications

References 7 publications

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Estimating population size using capture-recapture encounter histories created from point-coordinate locations of animals

Methoden der Bestandserfassung in der Ornithologie: Übersicht und kritische Betrachtung

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