TY - JOUR
T1 - Population decline of the noisy scrub-bird is not correlated with territory size, marginal declines in rainfall or fire impacts
AU - Dale Roberts, J.
AU - Danks, Alan
AU - Berryman, Abby
AU - Sidhu, Nadisha
AU - Burbidge, Allan H.
AU - Comer, Sarah
PY - 2020/9
Y1 - 2020/9
N2 - The noisy scrub-bird is endangered and confined to one natural population on Mount Gardner and several translocated populations east of Albany, Western Australia. Annual monitoring of the number of singing males at Mount Gardner since 1966 indicates a steady rise in numbers, peaking at 179 birds in 1994 followed by a less regular decline to 19 by 2017. The Lakes, an adjacent location, had a similar pattern of increase from the early 1970s then irregular decline from the mid-1980s. Broken stick regression models confirmed that both apparent patterns represented significant increase then decline in the number of singing males. Territory size estimates from 1994, 2005 and 2014 suggest an increase in size of territories over time but that pattern was not significant when only common territories were compared. Variance in bird numbers was not correlated with annual rainfall, which has broadly declined over the study period, or with number of rain days. We discuss five possible causes of decline: (1) inbreeding, (2) control of exotic predators and associated impact on non-target, natural predators, (3) resource/food availability (which may interact with rainfall), (4) removal of birds for introduction programs, and (5) the absence of wildfire and associated changes (senescence) in vegetation. None are compelling, single explanations for decline but their collective impact may be high. Survival of the noisy scrub-bird may be increasingly dependent on the introduced, managed populations of this species at Mount Manypeaks and on Bald Island.
AB - The noisy scrub-bird is endangered and confined to one natural population on Mount Gardner and several translocated populations east of Albany, Western Australia. Annual monitoring of the number of singing males at Mount Gardner since 1966 indicates a steady rise in numbers, peaking at 179 birds in 1994 followed by a less regular decline to 19 by 2017. The Lakes, an adjacent location, had a similar pattern of increase from the early 1970s then irregular decline from the mid-1980s. Broken stick regression models confirmed that both apparent patterns represented significant increase then decline in the number of singing males. Territory size estimates from 1994, 2005 and 2014 suggest an increase in size of territories over time but that pattern was not significant when only common territories were compared. Variance in bird numbers was not correlated with annual rainfall, which has broadly declined over the study period, or with number of rain days. We discuss five possible causes of decline: (1) inbreeding, (2) control of exotic predators and associated impact on non-target, natural predators, (3) resource/food availability (which may interact with rainfall), (4) removal of birds for introduction programs, and (5) the absence of wildfire and associated changes (senescence) in vegetation. None are compelling, single explanations for decline but their collective impact may be high. Survival of the noisy scrub-bird may be increasingly dependent on the introduced, managed populations of this species at Mount Manypeaks and on Bald Island.
KW - breeding success
KW - long-term monitoring
KW - translocation
UR - http://www.scopus.com/inward/record.url?scp=85091885063&partnerID=8YFLogxK
U2 - 10.1071/PC19029
DO - 10.1071/PC19029
M3 - Article
AN - SCOPUS:85091885063
SN - 1038-2097
VL - 26
SP - 230
EP - 238
JO - Pacific Conservation Biology
JF - Pacific Conservation Biology
IS - 3
ER -