Status of the Red Knot (Calidris canutus) in Louisiana Draft, 29 Nov 2013

Transcription

1 Status of the Red Knot (Calidris canutus) in Louisiana Draft, 29 Nov 2013 Audubon Louisiana Report Erik I. Johnson, Ph.D., Director of Bird Conservation 6160 Perkins Rd., suite 135 Baton Rouge, LA

2 Background Red Knots (Calidris canutus) are holartic in distribution with six subspecies recognized, each with largely distinct migration strategies (Figure 1). Although this species breeds on the high arctic tundra, they are almost exclusively coastal in winter, foraging on soft sands and mud in tidal estuaries and along coastlines for bivalves, small snails and crustaceans (Harrington 2001). Three subspecies breed in North America, and two of these winter in the Western Hemisphere (C. c. roselaari and C. c. rufa) with the third (C. c. islandica) wintering in the Eastern Hemisphere (Figure 1; Niles et al. 2010). C. c. roselaari winters primarily on the Pacific coast of North America, although perhaps a few winter in the western Gulf of Mexico (D. Newstead, pers. comm.), and the focal subspecies of this report, C. c. rufa, winters on Atlantic and Gulf of Mexico coasts of the Western Hemisphere. Figure 1. Red Knot distributions and known migratory connectivity. The darker shaded gray areas indicate known breeding distributions, the size of the black dotes indicate relative population size, and the black lines and arrows indicate known or assumed migratory routes. From Niles et al C. c. rufa, has declined by about 75% since the 1980s, and has a complicated non breeding distribution that includes at least three modestly distinct wintering grounds (Niles et al. 2010). The largest wintering population is found in southern South America, particularly in and around Tierra del Fuego in Chile and Argentina. This population has seen dramatic declines from about 65,000 birds in 1986 to about 17,000 in 2006 to about 10,000 in A second population in northeast Brazil, particularly, around Maranhão has seen much slower declines and probably holds about 7,500 birds. A third population winters in the southern U.S., with the majority found along the Gulf Coast of Florida, Texas, and between Georgia and South Carolina. Population sizes and trends are not well documented in these regions, but probably didn t number more than 12,000 15,000 birds in the 1980s (Harrington et al. 1988, Niles et al. 2010). Christmas Bird Count data suggest that the Gulf Coast population is declining at

3 2.3% per year ( %, 95% CI), representing a 60.6% decline ( %, 95% CI) over a 40 year span. Particularly in Louisiana and Texas, this species distribution barely overlaps CBC coverage, thus trends are strongly biased to counts from Florida (Niven and Butcher 2011). In this report, I summarize what is known about the distribution and population trends of Red Knots in Louisiana based on an examination of Christmas Bird Count, Audubon Coastal Bird Survey, International Shorebird Survey, and ebird data. Distribution Literature Review Lowery (1974) indicated that Red Knots are found in Louisiana year round, but they are substantially less common from mid June through July when the bulk of the population is breeding in the high arctic. Purrington (2008) listed Red Knots in southeastern Louisiana as an uncommon to common migrant, peaking in late March through May with a high count of 530 on 1 May 2004 and August through October. He also notes that a small number of birds are found along Louisiana s coast throughout the year, although over summering birds are non breeders, and are perhaps mostly sub adults (or perhaps some adults?), typically in a winter like plumage. ebird Data Maintained by Cornell Lab of Ornithology with support from the National Audubon Society, (ebird) has become a popular repository for bird watchers to submit their observations across the country since its launch in I summarized nearly 35 thousand hours of effort from 16,180 surveys submitted to ebird from within Louisiana s 2012 coastal zone boundaries (Table 1). I excluded surveys that lacked a measure of effort (i.e., number of party hours), and also excluded unpublished data from the Louisiana Winter and Summer Bird Atlases and other Louisiana State University Museum of Natural Science surveys. I summarized the amount of effort and number of Red Knots per party hour according to USGS 24K quadrangles that fall within or intersect with the coastal zone to look for patterns in relative abundance by region and season (spring [March May], summer [June July], fall [August October], winter [November February]). Table 1. The amount of bird watching effort in Louisiana s coastal zone contributed to the ebird database, summarized by season. Party hours Num. surveys Spring 12,883 6,000 Summer 1,907 1,218 Fall 8,692 4,043 Winter 11,455 4,919 Total 34,938 16,180

4 a) b) c) d) Figure 2. The effort (party minutes, not party hours as indicated in the legend) and Red Knot relative abundance reported in each USGS 24k quadrangle in spring (a), summer (b), fall (c), and winter (d).

5 The ebird data reflect the exclusively coastal distribution of Red Knots in Louisiana, although there are a few scattered records of Red Knots outside of the coastal zone in ebird. Among 456 reports of Red Knot from Louisiana in the ebird database, only 10 entries (2.2%) report 100 or more birds, and all of these are from southeastern Louisiana. Eight of these reports were from between 7 April and 21 May and the two fall surveys with > 100 birds reported were from 6 and 29 September. In all seasons, Red Knots are reported to have the greatest relative abundance in southeastern Louisiana (Figure 2). Survey effort again decreases east of the Mississippi River and along the Chandeleur Islands, although a survey from Breton Sound NWR (D. Muth, ebird) reporting a conservative estimate of 500 birds (the highest Louisiana count in the ebird database) suggests that some of these islands may occasionally or regularly support relatively large numbers of Red Knots during migration (Figure 2A). Submissions to ebird are relatively minimal along Vermilion Parish, Vermilion Bay, and the Point au Fer regions, and there are no reports of Red Knots from these areas (Figure 2). Audubon Coastal Bird Survey Data A collaboration between Baton Rouge Audubon Society, Pascagoula River Audubon Center, Louisiana State University, and National Audubon Society s Gulf Coast Initiative launched the Audubon Coastal Bird Survey (ACBS) in May 2010 in response to the Deepwater Horizon Oil Spill from Louisiana to Alabama (Johnson 2011). The program has grown in scope to include TX and there are currently 65 survey routes that are surveyed by citizen scientists. Modeled after the International Shorebird Survey initiated in the early 1970s organized by the Manoment Center for Conservation Sciences, ACBS surveys are scheduled run approximately every 10 days from 20 August and 30 October, 10 January and 20 February, and 20 March and 30 May. Additional monthly surveys are also sometimes added between focal survey periods. Realistically, there is not enough volunteer capacity to have complete simultaneous coverage across all routes, but 282 surveys have been completed from 21 routes in Louisiana between January 2011 and May Included in this effort are 40 surveys from 4 routes conducted monthly to bi monthly by Barataria Terrebonne National Estuary Program (BTNEP), with assistance from Audubon Louisiana, along the Caminada Headlands starting in September 2012 (Table 2). I summarize the data here similar to the ebird dataset, broken into three periods: spring (March May), fall (August October), and winter (November February); too few surveys have been conducted in summer (June July) to include here. Red Knots have been reported from 67 of 282 (23.8%) ACBS and BTNEP surveys, ranging in number from 1 to 55 birds when detected (Figure 3). In southwestern Louisiana, Red Knots were been reported from in winter and in limited density in spring with an average of < 1 bird/km per site. At all seasons, but particularly in spring and winter, Red Knots were reported in relatively higher densities in southeastern LA (Figure 4).

6 Table 2. Number of surveys conducted at each Audubon Coastal Bird Survey and Barataria Terrebonne National Estuary Program (*) survey site by season. Site Name Parish Fall Spring Winter Total Smith Bayou Cameron Peveto Woods Beachfront Cameron Holly Beach Cameron East Jetty Cameron Broussard Beach West Cameron Broussard Beach East Cameron Rutherford Beach Cameron Freshwater Bayou East Vermilion Rainey Beach Vermilion Trinity Island West Terrebonne Trinity Island East Terrebonne Wisner West* Lafourche Wisner East* Lafourche Bayou Moreau* Lafourche Elmer s Island West* Jefferson Elmer s Island East Jefferson Grand Isle West Jefferson Grand Isle King Tarpon Park Jefferson Grand Isle State Park Jefferson Lake Pontchartrain Westend Marina Orleans New Orleans Lakeshore Drive Orleans Total Raw count of Red Knot Rank Abundance Figure 3. A rank abundance curve of Red Knot counts from 68 Audubon Coastal Bird Surveys between Jan 2011 and May 2013 when Red Knots were present, ranging from 1 to 55 birds.

7 a) b) c) Figure 4. The relative density of Red Knots found across 17 Audubon Coastal Bird Survey and 4 Barataria Terrebonne National Estuary Program survey sites in spring (a), fall (b), and winter (c). Color codes indicate relative density of birds (see legend).

8 Population Trend Christmas Bird Count Data The most consistent long term data on Red Knot trends come from coastal Christmas Bird Count surveys, but there are only four count circles in Louisiana that encompass coastal habitat suitable to Red Knots. Three of these count circles are in southwest Louisiana (Johnson s Bayou, Sabine NWR, and Creole) and one is in southeastern Louisiana (Grand Isle; Figure 5). Johnson s Bayou CBC has been conducted almost continuously since , except for the winter of due to reduced access as a result of Hurricane Rita. Sabine NWR CBC has been run continuously since Creole CBC has been run nearly continuously since except for and Grand Isle CBC has a more broken history with continuous surveys from to and then again almost continuously since except for LAJB LASA LACR LAGI Figure 5. Locations of the four coastal Louisiana Christmas Bird Counts. LAGI = Grand Isle, LACR = Creole, LASA = Sabine NWR, and LAJB = Johnson s Bayou.

9 Table 3. The number of surveys conducted per decade at four coastal Louisiana Christmas Bird Counts. LAGI = Grand Isle, LACR = Creole, LASA = Sabine NWR, and LAJB = Johnson s Bayou. Number of Surveys Number of Party hrs 1970s 1980s 1990s 2000s 1970s 1980s 1990s 2000s LAGI LACR LASA LAJB Frequency that Red Knots were detected per decade LAGI LACR LASA LAJB Relative Abundance (Birds / party hr) LAGI LACR LASA LAJB s 1980s 1990s 2000s s 1980s 1990s 2000s Figure 6. The change in frequency of detection (left) and relative abundance (birds/party hr; right) by decade at four Christmas Bird Count Circles in coastal Louisiana. LAGI = Grand Isle, LACR = Creole, LASA = Sabine NWR, and LAJB = Johnson s Bayou. Two important patterns emerge from the Christmas Bird Count data (Figure 6). First, both the frequency of detection and the relative abundance of Red Knots have declined since the 1970s and 1980s across all four sites; the decline at the Grand Isle CBC is 93%. Second, although never abundant in southwestern Louisiana, Red Knots have not been detected on those three CBCs since International Shorebird Survey A single coastal ISS route was surveyed 16 times between 6 January and 20 April 1982 on Grand Isle (B. Ortego). Red Knots were not observed on three surveys, and counts ranged from 0 to 2500 with an average of 372 and a median of 160 (SD = 631, SE = 158; Figure 7). This survey effort provides the two

10 highest state counts available, and with multiple counts >100, the change compared to contemporary ACBS routes is consistent with a decline of Red Knots in the Grand Isle region similarly indicated by the Christmas Bird Count data. Number of Red Knots Figure 7. The numbers of Red Knots reported from a single International Shorebird Survey route on Grand Isle, LA between 6 January and 20 April Summary Red Knots were perhaps never terribly common in Louisiana as passage migrants or during wintering compared to estimates from Texas and Florida; however, available historical data suggest counts greater than 100 were fairly regular in the 1980s. Today, Red Knots are rarely seen in numbers greater than 50 at a time. Although Red Knots were perhaps always more common along the barrier island systems in southeastern Louisiana than along the chenier plain coastline of southwestern Louisiana, they are now extremely unlikely to be seen in southwestern Louisiana, except perhaps a few scattered birds during migration. The cumulative evidence suggests substantial declines have occurred in Louisiana since the 1980s, although with limited data from coastal Cameron Parish and the Grand Isle areas. With such limited data available, it may never be possible to determine how much of this is a result of a shift in distribution (due to changes in habitat or other factors), versus representative of a regional population decline. Relatively high numbers of Red Knots may still be possible to see on remote barrier islands, but a combination of lacking data and a quickly changing landscape make this difficult to assess. Understanding foraging and movement strategies in the complex mosaic of estuaries and barrier islands

11 would help place changes in distribution and abundance in context, as well as provide a better understanding for developing conservation and restoration initiatives in coastal Louisiana. Research Questions These questions do not necessarily apply just to birds in Louisiana, being shared across the Gulf Coast population of Red Knots. What is the population size and trend of Louisiana birds? Are over summering birds part of the Gulf Coast winter population, or short stopping migrants from South America? Is the proportion of these birds relative to the total C. c. rufa population changing (increasing or decreasing)? If so, would this suggest a shift in migratory capacity or ability at the population level? What is the origin of migratory and wintering birds along the Gulf Coast? Do some wintering C. c. roselaari mix with wintering C. c. rufa, particularly in the western Gulf (both in distribution and individual flocks)? What are the migratory routes of Louisiana and other Gulf Coast birds? How isolated (genetically and in terms of annual site fidelity) are Louisiana and Gulf Coast birds from each other and from Caribbean and northern South American populations? As barrier island restoration and beach nourishment projects are implemented, what habitat microhabitat characteristics can be incorporated or improved to increase habitat quality for Red Knots? Acknowledgements Many thanks go out to the numerous people who have helped contribute to the datasets evaluated here. Manomet Center for Conservation Sciences provided data for the International Shorebird Survey. Many hundreds of volunteers helped contribute to the Christmas Bird Count and ebird databases, and thanks go out to the ebird team at Cornell University for maintaining the ebird database. Audubon Coastal Bird volunteers have helped provide some of the first seasonal density estimates for coastal Louisiana and their time and efforts have been greatly appreciated. Barataria Terrebonne National Estuary Program provided coastal survey data from Caminada Headlands. Literature Cited Harrington, B. A Red Knot (Calidris canutus).in A. Poole, editor. The Birds of North America Online Cornell Lab of Ornithology, Ithaca. Harrington, B. A., J. M. Hagan, and L. E. Leddy Fidelity and survival differences between two groups of New World Red Knots (Calidris canutus). Auk 105:

12 Johnson, E. I Audubon Coastal Bird Survey, First Annual Report, July National Audubon Society, Baton Rouge, LA. Niles, L., H. Sitters, A. Dey, and Red Knot Status Assessment Group Red Knot Conservation Plan for the Western Hemisphere. Western Hemisphere Shorebird Reserve Network. Version 1.1 Niven, D. K. and G. S. Butcher Status and trends of wintering coastal species along the northern Gulf of Mexico, American Birds 65:12 19.