Sentences with phrase «predation estimates»

Careful scrutiny reveals a number of flaws in the work, and challenges Nolen's suggestion that that the researchers involved «took a rigorous and conservative approach» when developing their headline - grabbing predation estimates.

Much of that effort has involved the untangling of predation estimates based on indefensible sampling and extrapolation, and — more important — decoupling the implied relationship between predation and population - level impacts.

This, coupled with the error inherent in using a simple average, pushes predation estimates lower.

(Actually, there are additional problems with the authors» predation estimates, which I'll address in a future post).

But the authors go further, generating predation estimates based on pure speculation, specifically that «non-respondents have 150 % the number of outdoor cats as respondents.»

Among those that have gained the most currency are the predation estimates from the Wisconsin Study, the American Bird Conservancy's figure for the proportion of birds in the diets of free - roaming cats, and Dauphiné and Cooper's estimate of free - roaming cats in the U.S.

Not exact matches

In the United States in 2004, researchers estimated annual losses due to coyote predation on sheep and cattle at $ 40 million.

Retaliation for livestock predation is the primary cause of jaguar deaths: 96 percent of the estimated 230 jaguar killings between 1989 and 2014 were attributed to this cause.

Biologists also have used the studies from Marra, Temple, and a number of others to estimate the total U.S. death toll for birds due to cat predation as more than a billion per year.

Marra and his colleagues extrapolated findings from 21 studies in the U.S. and Europe to come up with an estimate of 30 million to 80 million «unowned» cats and 84 million «owned» cats in the U.S., their kill rates, and other factors leading to bird predation.

(Oda's not the first one to mistake this for an estimate of predation across the country, however; Frank Gill made the same error in his book Ornithology.

Somebody explain to me, for example — just as a start --(1) why it's acceptable to use a uniform distribution in the context I describe above, and / or (2) how doing so is inconsequential to the predation «estimates.»

``... the ecological and conservation significance of these kill tallies is difficult to contextualise, because (1) there are no reliable estimates of the total population of birds in Australia; (2) predation may fall disproportionately on some bird species; (3) some bird species may be able to sustain high mortality rates and maintain viable populations but others may not; and (4) as demonstrated here, there is substantial spatial variation in the numbers and proportion of birds killed across Australia.»

This study by Environment Canada scientist Peter Blancher was designed to create a credible estimate of the rates of bird predation by cats, identify information...

TNR supporters argue that estimates of cat predation are overblown and, in any event, TNR is the only successful way to manage cat populations.

Barratt has suggested that «median numbers of prey estimated or observed to be caught per year are approximately half the mean values, and are a better representation of the average predation by house cats based on these data.»

Impressive Estimates In «Free - Ranging Domestic Cat Predation on Native Vertebrates in Rural and Urban Virginia,» [2] published in 1992, the authors estimated that the state's 1,048,704 cats were killing between 3,146,112 and 26,217,600 songbirds each year.

The two inflated figures described in (1) and (2) are multiplied together, further inflating estimated predation rates.

The Studies In the first study, Baker et al. distributed questionnaires to 3,494 households across a 4.2 km2 area of northwest Bristol (UK), and used responses to estimate cat ownership and predation levels (via prey returned home).

So, whereas Dauphiné and Cooper (and others) suggest increasing such estimates by factors of two and three («predation rates measured through prey returns may represent one half to less than one third of what pet cats actually kill...» [14]-RRB-, they should, in fact, be reducing them by half.

``... median numbers of prey estimated or observed to be caught per year are approximately half the mean values, and are a better representation of the average predation by house cats based on these data.»

So, even setting aside the complexities of source - sink dynamics, these inflated predation rates, combined with the fact that «the estimates of breeding density presented in this manuscript should be regarded as minima,» [3] raise serious doubts about whether the site is in fact a habitat sink (or, if so, to what extent).

Of greater interest to me, though, are the assumptions Baker et al. used to estimate the impact of cat predation.

While Lepczyk et al. emphasize the potential for under - estimating predation levels, they never consider the risk of over-estimating these levels — or their most obvious potential source of error: landowners» recollections of birds killed.

This greatly overestimates potential predation, and leads them to conclude — erroneously — that the actual number of prey killed by cats was «3.3 times greater than the rate estimated from prey brought home,» [9] as was discussed previously.

Referring to the estimated 30 percent of House Sparrow mortality attributed to cat predation in the English Village study, Gary Patronek emphasizes the importance of viewing such predation in the larger context.

In their recently released book, The American Bird Conservancy Guide to Bird Conservation, ABC changes tack a bit — using what the authors call «conservative» estimates of the outdoor cat population and annual predation rates, for example, to arrive at their figure of «532 million birds killed annually by outdoor cats.»

«If the real objection to managed colonies is that it is unethical to put cats in a situation where they could potentially kill any wild creature,» writes Patronek, «then the ethical issue should be debated on its own merits without burdening the discussion with highly speculative numerical estimates for either wildlife mortality or cat predation.»

We conducted 10,000 random draws to estimate a potential range of annual predation on each wildlife taxa.

Studies were only included if: (1) they clearly reported cat ranging behaviour (that is, a description of whether cats were owned or un-owned and whether they were outdoor cats or indoor - outdoor cats), and (2) the group of cats investigated fit exclusively into one of the two groups we defined above (that is, we excluded studies that lumped owned and un-owned cats in a single predation rate estimate).

We included studies that used cat owners» records of prey returns, but we excluded those that asked owners to estimate past prey returns because such questionnaires may lead to bias in estimation of predation rates39.

We excluded studies from outside temperate regions and those with predation rate estimates based on fewer than 10 cats, < 1 month of sampling, or on cats that were experimentally manipulated (for example, by fitting them with bells or behaviour altering bibs).

Our finding that un-owned cat population size and predation rate explained the greatest variation in mortality estimates reflects the current lack of knowledge about un-owned cats.

Mean predation rates within each square each season were multiplied by cat density to estimate the total number killed, and summed across seasons to estimate the number killed annually.

As the numbers of cats declined, the last having been killed in 2000, the rabbit population increased, to an estimated 100,000 by 2007 ---- and rabbit damage to bird nesting habitat proved far more damaging to the sea bird population than cat predation ever had been.

Despite the scarcity of direct observations, evidence for the existence of large arctic cod aggregations in winter was traditionally derived from the intensive predation rate estimated from the stomach content of marine mammals and birds later in the season (Welch et al. 1992).

«These estimates emphasize the important role that spider predation plays in semi-natural and natural habitats, as many economically important pests and disease vectors breed in those forest and grassland biomes,» says lead author Nyffeler.