All years aren’t created equally

17 December, 2017 (updated 2 January, 2018)

Note: the following analysis is confined to ‘Continental’ portion of ABA area, and employs the current (8.0.1) ABA checklist. It also borrows heavily from the ABA Rarities Report blogs, eBird data, and the Big Year data sets of birding historian Joe Lill.

In these days of growing interest in ABA Big Years, participants are becoming more strategic in their planning, and more focused on their results. It’s a ‘given’ that the serious contestant is likely to tick all of the 672 ‘common’ species (Codes 1 & 2) from the ABA checklist prior to the dreaded end-of-year buzzer. The real measure of success is the number of ‘coded’ species (Codes 3-5) that are ticked from that same checklist. Unfortunately for some contestants, not all years will provide equally generous opportunities to rack up long lists of rare bird species - irrespective of how much planning and effort is applied. Timing, it seems, can be an overriding factor in determining the outcome of an ABA big year. So a comparison of the annual numbers of rare bird species reported within the area is a prerequisite to identifying any correlations between 'good' (and 'bad') years, and corresponding climatic trends such as to El Nino and La Nina events. At the time of writing a La Nina event has well and truly developed, following a transition from El Nino conditions in mid-2016. 

My interest in possible cyclic nature of 'good' and 'not-as-good' years for rare birds in the ABA area has recently piqued while following the progress of the leading five 2017 big year birders (Yve, Ruben, Victor, Gaylee and Richard). All chocked up impressive year-lists, with a high-paced run to the finish line. To get a better grip on the relative 'birdiness' of recent years, I decided to assess the annual variation in species counts on the eBird online platform via the Species Maps section of the webpage 
https://ebird.org/ebird/map/ .  I also consulted with the weekly ABA Rare Bird Report blogs, accessed from the ABA website. For the purposes of this exercise, Hawaiian sightings have not been considered, as that would add more confusion than clarity to the sorts of trends we’re trying to identify.

In a perfect world, the number of coded species reported on eBird in a given year could be regarded as a reflection what’s going on in the field – e.g. if 2016 had 37% more rare species reported than did 2012 (and it did), then it would be nice if we could assume that there were about a third more rare bird species bouncing around the ABA area in the later year. But it probably isn’t that simple; other factors are likely to include the ever-improving bird-reporting systems – with increasing use of eBird, the increasing interest in birding (resulting in more birders stomping around out there - hopefully occasionally encountering unusual birds), increased strategically-timed pelagic birding opportunities, and possibly improved coverage of the Alaskan outposts by dedicated birders and birding tours (though it seems that numbers of birders venturing to the islands substantially swell and wane on an annual basis in reaction to the relative successes of the previous year). Taxonomic changes present an additional consideration - at least in the longer term, with the net effect of all those splits and lumps gradually swelling the number of prospective coded bird possibilities.

After crunching the eBird numbers, I generated two different versions of the summaries. Table 1 provides a straight-up year-by-year comparison of the number of rare bird species reported at least once on the eBird registry and/or the ABA Rare Bird Report. Later, in Table 2, I’ve differentiated between reported rarities that the serious big year birder might have had a good chance of sighting at some time during the year, and those species that couldn’t readily have been converted to ‘ticks’ , even by the most gung-ho of twitchers on any occasion that year (e.g. one-day-wonders).

Table 1. Summary of the number of ‘coded’ bird species reported annually on eBird from 2011-2017*

2011
2012
2013
2014
2015
2016
2017
Code 3
74
68
75
71
73
79
78
Code 4
49
34
43
39
47
53
55
Code 5
15
9
14
11
19
19
25
Total:  
136
111
132
121
139
151
158








As suggested earlier, I thought it might be interesting, at least to my fellow Big Year birders - past, present, and future, to categorize the rarity reports from each of the last six years on the somewhat subjective basis of ‘twitchability’. Obviously, not all reported rare birds can be chased down by even the most cashed-up and reactive birders; many are observed only fleetingly - perhaps with a single sighting by a single birder. Hence, the total number of rare species reported in a given year is not the same as the number of rare species accessible to that year's listers. It doesn’t really help if a Code 5 Eurasian Wryneck shows up on a no-access military installation off the California coast, or if an Atlantic Yellow-nosed Albatross is seen only on a single pelagic trip out of New York. At the other extreme of the ‘twitchability’ scale, a Tufted Flycatcher in Madera Canyon with a months-long history of almost daily sightings in a heavily-birded public place, is pretty much a ‘dead cert’, as the Australian birders would say. 

For the sake of satisfying my own curiosity, I created a practical set of criteria to try to distinguish between incidences of ‘twitchable’ versus ‘un-twitchable’ individual rare birds, by screening thousands of eBird reports generated from 2012-17. An inadequate description and justification of those criteria is provided further down the page. 

Table 2. Number of rare bird species reported in each of the past six years are separated into two groups – ‘twitchable’ and ‘untwitchable’. I ran out of steam before breaking down the 2011 reports!

2012
2013
2014
2015
2016
2017*
untwitchable
29
36
35
29
35
37
twitchable
83
96
86
110
116
121
total
111
132
121
139
151
158

To qualify for ‘twitchable’ status during a given year, a species must have presented the keen twitcher with at least one opportunity for a fair shot at encountering it. In most cases, this was established when, after a report was made, subsequent day-reports were timed in a manner conducive to a successful twitch. My definition of 'conducive timing' is that when a cluster of two or more day-reports for an individual bird occurs, the bird will have been deemed twitchable any time when two day-reports occurred with no more than two 'reportless' days between them. The idea with the prescribed maximum period for no sightings is that that after two days of dipping, the twitcher could be forgiven for moving on. In those instances in which sightings were confined to two back-to-back days, I erred on the ‘untwitchable’ side.

Of course, in practice, many birders ultimately rely upon their gut feelings about the ‘stickability’ of freshly-reported birds to decide whether or not to hightail it to the airport. Some, including myself during non-'big'-years, will automatically invoke the ‘two-day’ or ‘three-day’ rule (that's me) – wherein the bird needs to be relocated for a second, or perhaps third day before flights are booked. Predominant factors that affect the decision to jump - or not, include costs and inconvenience. For big year birders however, the element of desperation can become an overriding factor. The especially motivated player can expend big efforts and blow travel budgets adopting the ‘fly first and ask questions later’ approach, only to accumulate a soul-destroying string of dips (it's true, believe me). 

For the purpose of this exercise I’ve approached the twitchability issue for pelagic bird species a little differently. Coded seabirds that typically show up at least four or five times per year during the peak seasons (Spring in the east, Autumn in the west) are regarded as twitchable - even if it might require up to a half-dozen day trips to secure a sighting. Examples of these include Flesh-footed Shearwater, Buller's Shearwater, Least Storm-petrel, and Craveri’s Murrelet on the west coast (it required 14 day trips and a 8 wishful whale-watch missions for me to secure all four of these); and Great Skua, Fea’s Petrel, and Trindade Petrel (never did get this one) on the east coast.

Due to the limitations of this little study, there aren’t any earth-shaking conclusions to draw beyond the fact that there does appear to be significant year-to-year variation in the number of rare bird species reported in the ABA area. The annual rates of reported rare species and ‘twitchable’ species share similar graph curves, suggesting that the simpler, less subjective indicator of ‘good’ vs ‘not-as-good’ years for big year birders might be a straightforward index of reported coded species per year. In other words, potential for epic Big Year results can in part be measured - albeit in retrospect, by the number of coded species reported on eBird that year. And so, with the benefit of 20:20 hindsight, it appears that the current year of 2017 has eclipsed 2016 as the best twitching year to date. On the one hand, its not hard to conclude that after a string of good years, we're due for a couple of years of low rarities numbers. But an alternative 'half-glass-full' interpretation might be that the upward trajectory of rare bird species numbers in the ABA area over the past four years might be due to the increasing presence of birders 'out there' with greater use of eBird, and is likely to continue as a trend. Whichever way things go in 2018, I'll happily let you know just how full that glass really was - by the end of the year.


So, just how important is El Nino?
Looking at Diagram 1 taken from the NOAA weather data (below), it looks as if the bumper years of 1998 (Sandy Komito’s massive Big Year), and 2016 both occurred on the tail end of El Nino events. But the best-ever year for rarities to date (2017) did not. It seems likely that the steady increase in eBird usage, and ever-growing birding intensity throughout the region is at least partially responsible for elevated rarity detections in recent years. But its  also apparent that 2017 saw favourable winds blowing extraordinary numbers of rare birds into the ABA area. Whether or not the heaven-sent westerlies pushing Asian migratory birds to Gambell, or the bird-laden weather systems that slammed into Florida were part of any identifiable cyclic weather events is not obvious. For now at least, it looks as if the significance of El Nino conditions in stimulating increased vagrancy of rare birds into the ABA area remains unproven.  











Bonus table: A comparison of the rarity counts of some of the more recent Big Year birders as a proportion of the rare bird species reported on eBird at least once during ‘their’ year, again borrowing from the mine of data curated by Joe Lill.



Year
Birder
Rarities in
Rarities by
Percentage
Continental ABA area
Birder
2011
John Vanderpoel
138
83
60%  
2013
Neil Hayward
132
83
63%
2016
John Weigel
151
111
74%
2016
Olaf Danielson
151
107
71%
2016
Laura Keene
151
94
62%
2016
Christian H.
151
82
54%
2017
Yve Morrell
158
90
57%