在今年度的「後院數鳥」(The Great Backyard Bird Count)活動中，十種最常見的鳥類包含了北美紅雀、藍羽松鴉、烏鴉和知更鳥。但活動人員指出，今年活動最值得注意的結果是許多鳥種消失了。
後院數鳥活動是由美國奧杜邦協會（National Audubon Society）、 康乃爾鳥類學實驗室（Cornell Lab of Ornithology）及加拿大鳥類研究(Bird Studies Canada) 一起合作的計畫。這個活動參與者沒有年齡限制，可從統計結果得知600多種鳥類的分佈。
「在活動中發現新的或很稀少的鳥類，總是會使我們狂喜，」奧杜邦教育中心田野支援部西區主任派迪(Robert Petty)說：「以今年來說，在德州麥卡倫(McAllen)看到的朱領錫嘴鳥 (crimson-collared grosbeak)，是在2005年活動中第一次出現的。」
如往年一般，今年的報告反應了外來鳥種族群在北美大陸的持續擴張。12年前，只有九個州有記錄到灰斑鳩(the Eurasian collared-dove)，但是今年共有39個州觀察到超過14,000隻的灰斑鳩。
今年聖地牙哥(San Diego)海岸邊的賞鳥志工可以享受到觀賞紅嘴熱帶鳥(red-billed tropicbird)的樂趣，那是今年活動中第一次被觀察到的鳥類。
在加拿大渥太華的馬拉松(Marathon, Ontario) 驚人地觀察到一隻灰冠玫瑰雀 (gray-crowned rosy finch)，牠們通常出現在洛基山脈(the Rocky Mountains)，距離馬拉松非常遠。
「數鳥活動的資料隨著每年的累積變得越來越有價值，」加拿大鳥類研究計畫主任康寧(Dick Cannings) 說：「我們可以看出鳥類數目或分布的重要改變，這些可能會受到氣候、棲息地、疾病等等因素影響。」
後院數鳥活動由野鳥公司(Wild Birds Unlimited)部份贊助，明年的後院數鳥活動在2011年2月18-21日舉行。
Red cardinals, blue jays, black crows and robins were among the 10 most sighted birds in this year's Great Backyard Bird Count, but organizers said one of the most dramatic results from this year's count was the absence of other bird species.
The Great Backyard Bird Count is a joint project of the National Audubon Society and the Cornell Lab of Ornithology with Canadian partner Bird Studies Canada. It is open to bird watchers of all ages. The results provided a snapshot of the whereabouts of more than 600 bird species.
The 13th annual Great Backyard Bird Count was a record-breaking year for participation. During the four-day event in February, more than 97,200 bird checklists were submitted by an estimated 63,000 volunteer bird watchers from across the United States and Canada.
Checklists came in from all 50 states and from all 10 provinces and three territories of Canada. Participants reported 602 species in 11.2 million individual bird observations.
From reports of rare species to large-scale tracking of bird movements, the Great Backyard Bird Count provides insight into the lives of bird populations.
"The new and the unusual are always a thrill during the Great Backyard Bird Count," said Robert Petty, western director of field support at Audubon's division of Education and Centers. "Notable sightings this year included a crimson-collared grosbeak in McAllen, Texas, the first time the species has been reported during the count since 2005."
"There's simply no better way to collect information about all these birds so quickly across such a large range," said Janis Dickinson, citizen science director at the Cornell Lab in Ithaca.
Over time, the Great Backyard Bird Count has recorded dramatic swings in the numbers of these species reported from year to year. These fluctuations may be influenced by the birds' food supply and reproductive success far to the north. This year, they presumably did not need to travel as far south to find enough food.
Results from this year's count also documented the continuing expansion of an introduced species across the continent. A dozen years ago, the Eurasian collared-dove was reported in nine states during the bird count. This year more than 14,000 of these doves were reported in 39 states and provinces.
Birders off the coast of San Diego were treated to a red-billed tropicbird - the first verified sighting of this species for the Great Backyard Bird Count.
In Marathon, Ontario, a gray-crowned rosy finch was a spectacular sighting because it was far outside its normal range in the Rocky Mountains.
"GBBC data become more and more valuable with each passing year," said Dick Cannings, program director for Bird Studies Canada. "Over time we'll be better able to see significant changes that may occur in the numbers and distributions of birds which may be tied to climate change, habitat loss, disease, or other factors."
The Great Backyard Bird Count is sponsored in part by Wild Birds Unlimited. The next Great Backyard Bird Count is February 18-21, 2011.