Posted by: Dan | October 23, 2009

How Many Birds Killed?

This is part of the series of posts Poaching in Cyprus FAQ

Approximately how many birds are killed seasonally?

BirdLife Cyprus derives its estimates regarding the number of birds trapped from observations of the number of limesticks and nets observed during monitoring, which is done by previously described surveillance methods. The direct findings from BirdLife’s monitoring schemes were published most recently in an Autumn 2008 report, released 15 January, 2009. (Other reports: 2009.) Their 2008 data, used to explain the calculations:

fig1-fall08

fig2-fall08

Thus, for Autumn 2008 (from the Appendices to the report):

Limesticks: Estimated total number of limesticks set per day in survey area = [total number of fresh (new) limesticks recorded in survey squares] x [total number of ‘possible bird trapping area’ squares/ number of squares surveyed]

…Estimated total number of limesticks set per day in survey area = [199] x [301/ 100] = 599

Active net rides: Estimated total length of active net rides in survey area = [total length of net rides in categories P, ANN, AUN and ASN recorded in survey squares] x [total number of ‘possible bird trapping area’ squares/ number of squares surveyed]

…Estimated total length of active net rides in survey area = [2,302] x [301/100] = 6,929 m

According to accounts from trappers recorded in Magnin’s 1987 report to the IUCN (and corroborated elsewhere), an individual limestick catches a bird every other day on average, while a standard 12 m long mist net catches 20 birds a day on average.

Limestick Catch: Total number of birds caught on limesticks in the survey area =
Estimated total number of limesticks set per day in survey area x ½ x length of trapping season in days

… Estimated total number of birds caught on limesticks in the survey area = 599 x ½ x 60 = 17,970

Mist Net Catch: Prepared (P) net rides are assumed to have been in use only every other day during the trapping season, while net rides in the ANN, ASN and AUN category are assumed to have been in use every day. Total numbers of birds caught in nets in the survey areas = {((Total length of P category net rides/2) + (Total length of ANN+AUN+ASN rides)) x (total number of ‘possible bird trapping area’ squares/ number of squares surveyed)}/12 [length of average net] x 20 birds per net per day x length of trapping season in days

… Estimated total numbers of birds caught in nets in the survey areas = {((855/2) + (1,447)) x (301/100)}/12 x 20 x 60 = 564,224

An estimate for the Island-wide trapping toll can be arrived at based on the assumption that the extended Famagusta and Ayios Theodoros – Maroni survey areas account for 75% of trapping activity across the island.

Therefore, for autumn 08, the total, Island-wide catch can be estimated at 776,258 birds (for nets and limesticks combined).

Though the above estimates may, arguably, be inflated by the assumptions about frequency of use of net rides and by the fact that, beyond a certain (unknown) point, catch rate per net is in practice likely to decline as the number of nets set increases (non-linear relationship), it is worth noting that that there are also possible sources of underestimate:

  1. Not all limesticks or mist netting activity will have been detected within survey squares (especially where trapping within enclosures is concerned).
  2. More recent statements from trappers in local newspapers suggest the catch rates suggested by Magnin (1987) for limesticks and, in particular, for nets, are underestimates.
  3. The actual length of the trapping season may be longer than the 60 days assumed above.

Thus it seems as though the estimate of 776,000 birds slaughtered in Autumn 2008 is a very conservative figure. That’s a boatload of birds by itself, so don’t be fooled by the fact that the data from recent years looks small in comparison to 2002 and 2003.

And as you can see by comparing the estimates for birds trapped by limesticks in the study area (17,970 birds) versus birds trapped by mist nets in the study area (564,224 birds), mist nets are the worse of the two. This makes the upswing in mist netting all the more worrying.

fig3-fall08


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