Are South Hills Crossbills declining with increasing temperatures?
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Master's thesis presentation. Background biology on South Hills Crossbills, documentation of population decline, and proposed conservation efforts.
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Are South Hills Crossbills declining with increasing temperatures?
- 1. Are South Hills Crossbills Declining with Increasing Temperatures? Julie Hart Master’s Defense Zoology & Physiology 29 April 2013
- 2. INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS EXTINCTION RISK .............................................................. Extinction risk from climate change Chris D. Thomas1 , Alison Cameron1 , Rhys E. Green2 , Michel Bakkenes3 , Linda J. Beaumont4 , Yvonne C. Collingham5 , Barend F. N. Erasmus6 , Marinez Ferreira de Siqueira7 , Alan Grainger8 , Lee Hannah9 , Lesley Hughes4 , Brian Huntley5 , Albert S. van Jaarsveld10 , Guy F. Midgley11 , Lera Miles8 *, Miguel A. Ortega-Huerta12 , A. Townsend Peterson13 , Oliver L. Phillips8 & Stephen E. Williams14 1 Centre for Biodiversity and Conservation, School of Biology, University of Leeds, Leeds LS2 9JT, UK 2 areas7–12 . This ‘climate envelope’ re which populations of a species cu competitors and natural enemies. mated by assuming that current env projected for future climate scenario either has no limits to dispersal su becomes the entire area projected by that it is incapable of dispersal, in wh the overlap between current and fut example, species with little dispers landscapes)11 . Reality for most speci extremes. le The responsiveness of species to recent1–3 an change raises the possibility that anthropogenic could act as a major cause of extinctions in the nea Earth set to become warmer than at any period in t (ref. 6). Here we use projections of the future 1,103 animal and plant species to provide ‘first-p extinction probabilities associated with climate cha 2050. For each species we use the modelled association climates (such as temperature, precipitation and present-day distributions to estimate curre NATURE | VOL 427 | 8 JANUARY 2004 | www.nature.com/nature
- 3. South Hills (Type 9) AFLP VARIATION IN CROSSBILLS 1 AFLP VARIATION IN CROSSBILLS 1881 overlapping clusters when the analysis was restricted ed crossbills. nly three of nine comparisons of different geographic ples within call types revealed significant genetic erentiation, which contrasts with the relatively high mber of comparisons that were significant between call es (25 of 28 comparisons; Fisher’s exact test, P = 0.002). significant within-call-type comparisons were between type 2 in the Black Hills, South Dakota, and both the dia Mountains, New Mexico (FST = 0.057, P < 0.05), and samples of call type 2 from different geographic loc (Fig. 1) indicates that the vast majority of variat found within location (97%) but that a significant a of variation (3.1%) was due to differences among loc which was lower than the 7% explained by diffe among call types (Table 3). Finally, different geog samples within call types 1, 2, and 5 grouped tog in the upgma dendrogram (Fig. 4), suggesting g continuity within these call types, whereas th geographically separate samples of call type 7 d 4 upgma phylogram reflecting relative genetic distances based on pairwise estimates of Nei’s D among different recognized uded in this study and eight call types of the red crossbill complex including samples from two geographic samples of call typ 7, and four geographic samples of call type 2 (BP, Bears Paw Mountains; NM, New Mexico; BH, Black Hills; LR, Little Rocky Mou the samples taken in 2000 and 2001 distinguished as LRa and LRb, respectively). Values at the nodes represent bootstrap suppor 000 replicates; values < 50% are not shown. A representative head and, where known, a cone of the conifer on which each c ializes is shown. Heads and cones are from figures in Benkman (1987b, 1999), Parchman & Benkman (2002) and Farjon & Styles bill sizes and cones altered to reflect relative sizes among the different crossbills and conifers, respectively. Cones from top to Pinus occidentalis, Picea mariana, Pinus contorta latifolia from South Hills, Pinus ponderosa scopulorum, Pinus contorta latifolia ophylla, Pseudotsuga menziesii menziesii, and Picea rubens. Call type 4 is associated with Pseudotsuga m. menziesii. 4 upgma phylogram reflecting relative genetic distances based on pairwise estimates of Nei’s D among different recognized ded in this study and eight call types of the red crossbill complex including samples from two geographic samples of call typ 7, and four geographic samples of call type 2 (BP, Bears Paw Mountains; NM, New Mexico; BH, Black Hills; LR, Little Rocky Mou the samples taken in 2000 and 2001 distinguished as LRa and LRb, respectively). Values at the nodes represent bootstrap suppor ylogram reflecting relative genetic distances based on pairwise estimates of Nei’s D among different recognized species tudy and eight call types of the red crossbill complex including samples from two geographic samples of call types 1, 5, ographic samples of call type 2 (BP, Bears Paw Mountains; NM, New Mexico; BH, Black Hills; LR, Little Rocky Mountains, taken in 2000 and 2001 distinguished as LRa and LRb, respectively). Values at the nodes represent bootstrap support based phylogram reflecting relative genetic distances based on pairwise estimates of Nei’s D among different recognized species his study and eight call types of the red crossbill complex including samples from two geographic samples of call types 1, 5, Type 2 Type 3 Type 4 Type 5 Type 1 ig. 4 upgma phylogram reflecting relative genetic distances based on pairwise estimates of Nei’s D among different recogniz ncluded in this study and eight call types of the red crossbill complex including samples from two geographic samples of call nd 7, and four geographic samples of call type 2 (BP, Bears Paw Mountains; NM, New Mexico; BH, Black Hills; LR, Little Rocky M with the samples taken in 2000 and 2001 distinguished as LRa and LRb, respectively). Values at the nodes represent bootstrap sup INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS RED CROSSBILL Birds of North America
- 4. SOUTH HILLS CROSSBILL INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS Proposed species based on: • Deeper bill • Unique call type • Resident • Seasonal nesYng • Low hybridizaYon • GeneYc differenYaYon Benkman et al. 2009, Condor
- 5. INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS STUDY AREA South Hills: 1530 km2 in area 65 km2 lodgepole pine
- 6. INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS STUDY AREA ElevaYon: 1277 to 2457 m
- 7. INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS PREVIOUS FINDINGS 2003 2004 2005 2006 2007 2008 0 50 100 150 200 250 300 350 Year Crossbilldensity(individuals/km2) Year San;steban et al. 2012, Journal of Animal Ecology 63% decline R2 = 0.97, P < 0.001
- 8. HYPOTHESIS Warmer temperatures cause seroYnous cones to open and drop their seed, reducing the amount of food for crossbills and leading to their decline. INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS Less food
- 9. RESEARCH QUESTIONS • Is crossbill density conYnuing to decrease? • Do changes in survival account for the observed changes in density? • Is crossbill survival related to climate? • Is cone producYvity decreasing? INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS
- 10. RESEARCH QUESTIONS INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS • Is crossbill density conYnuing to decrease? • Do changes in survival account for the observed changes in density? • Is crossbill survival related to climate? • Is cone producYvity decreasing?
- 11. POINT COUNTS INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS 74 points
- 12. • 10-‐minute counts with distance sampling • 1041 birds in 6660 minutes of observaYon • Analyzed with standard methods including a correcYon factor for detectability • Used program DISTANCE to esYmate density INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS POINT COUNT ANALYSIS
- 13. CROSSBILL DENSITY INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS ● ● ● ● ● ● ● ● ● Year Crossbilldensity(individualskm−2 ) 2003 2005 2007 2009 2011 0 50 100 150 200 250 300 350 R2 = 0.98, P < 0.001 14% annual decline 277 birds/km2 71 birds/km2 75% decline
- 14. Cerulean Warbler (-‐3%) CROSSBILL DECLINE INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS Bicknell’s Thrush (-‐7%) Rusty Blackbird (-‐10%) South Hills Crossbill (-‐14%)
- 15. RESEARCH QUESTIONS INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS • Is crossbill density conYnuing to decrease? • Do changes in survival account for the observed changes in density? • Is crossbill survival related to climate? • Is cone producYvity decreasing?
- 16. MARK-‐RECAPTURE STUDY INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS
- 17. MARK-‐RECAPTURE ANALYSIS INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS Bird ID Year1 Year2 Year3 Year4 Capture History Survival Bird1 1 1 1 1 1111 1111 Bird2 1 1 0 1 1101 1111 Bird3 1 0 0 0 1000 1??? ɸ = survival probability = 𝒇(year, sex) 𝜌 = capture probability = 𝒇(year, sex) 𝓛(ɸ, 𝜌 ⎪ capture histories) n = 1238 adults tracked from 2000 to 2012
- 18. MARK-‐RECAPTURE ANALYSIS INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS Bird ID Year1 Year2 Year3 Year4 Capture History Survival Bird1 1 1 1 1 1111 1111 Bird2 1 1 0 1 1101 1111 Bird3 1 0 0 0 1000 1??? ɸ = survival probability = 𝒇(year, sex) 𝜌 = capture probability = 𝒇(year, sex) 𝓛(ɸ, 𝜌 ⎪ capture histories) n = 1238 adults tracked from 2000 to 2012
- 19. 1. Used program MARK 2. Modeled capture probability – 𝜌 ~ year + sex – higher for males than females 3. Modeled survival probability – ɸ = 𝒇(year, sex) – model-‐averaged INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS MARK ANALYSIS
- 20. INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS ANNUAL SURVIVAL ● ● ● ● ● ● ● ● ● ● ● Year Apparentadultsurvival±1SE 2000 2002 2004 2006 2008 2010 0.5 0.6 0.7 0.8 0.9
- 21. INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS ANNUAL SURVIVAL ● ● ● ● ● ● ● ● ● ● ● Year Apparentadultsurvival±1SE 2000 2002 2004 2006 2008 2010 0.5 0.6 0.7 0.8 0.9 Period Mean Survival 2000 -‐ 2003 0.68 2003 -‐ 2010 0.59 2010 -‐ 2011 0.67
- 22. SURVIVAL & DENSITY INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS PopulaYon ProjecYon • Life table analysis • Constant fecundity and juvenile survival • EsYmated density with model-‐averaged adult survival Year Crossbilldensity(individualskm−2 ) 2003 2005 2007 2009 2011 0 50 100 150 200 250 300 350
- 23. SURVIVAL & DENSITY INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS PopulaYon ProjecYon • Life table analysis • Constant fecundity and juvenile survival • EsYmated density with model-‐averaged adult survival Year Crossbilldensity(individualskm−2 ) 2003 2005 2007 2009 2011 0 50 100 150 200 250 300 350 ● ● ● ● ● ● ● ● ● Projected from survival
- 24. SURVIVAL & DENSITY INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS ● ● ● ● ● ● ● ● Year Crossbilldensity(individualskm−2 ) 2003 2005 2007 2009 2011 0 50 100 150 200 250 300 350 ● ● ● ● ● ● ● ● ● ● Point count estimate Projected from survival PopulaYon ProjecYon • Life table analysis • Constant fecundity and juvenile survival • EsYmated density with model-‐averaged adult survival
- 25. RESEARCH QUESTIONS INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS • Is crossbill density conYnuing to decrease? • Do changes in survival account for the observed changes in density? • Is crossbill survival related to climate? • Is cone producYvity decreasing?
- 26. CLIMATE COVARIATES Variable Variable definiYon NHOT(X) number of hot (≥32°C), dry (<1 mm) days (unweighted and weighted lags of 1-‐5 years) MSPR mean spring temperature (Mar – May) MSUM mean summer temperature (Jun – Aug) MANN mean annual temperature between captures (Jul – Jun) MNBY mean temperature in non-‐breeding year (Sep -‐ Mar) NCW number of cold (<5°C), wet (>1 mm) days USGS NRCS SNOTEL data, 1989-‐current 2 km from banding site INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS
- 27. SURVIVAL & CLIMATE Model ΔQAICc w R2 Φ(~MNBY) 0 0.59 0.59 Φ(~NHOT5) 1.66 0.26 0.51 Φ(~NHOT4) 4.16 0.07 0.40 Φ(~NHOT5.w33) 7.16 0.02 0.27 Φ(~MSPR) 7.56 0.01 0.25 Φ(~NHOT4.w33) 8.18 0.01 0.22 Modeled climate with survival Climate model = Φ(climate) 𝜌(year + sex) INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS
- 28. ● ● ● ● ● ● ● ● ● ● ● Mean temperature °C (September − March) Apparentadultsurvival −1.0 −0.5 0.0 0.5 1.0 1.5 2.0 0.55 0.60 0.65 0.70 0.75 LOWER SURVIVAL WITH WARMER TEMPS R2 = 0.55, P < 0.009 INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS ● ● ● ● ● ● ● ● ● ● ● Number of hot, dry days over previous five years Apparentadultsurvival 1.0 1.5 2.0 2.5 3.0 3.5 0.55 0.60 0.65 0.70 0.75 R2 = 0.52, P < 0.012 Number of hot, dry days over 5 previous years Mean temperature (°C) (September – March) Apparent survival
- 29. RESEARCH QUESTIONS INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS • Is crossbill density conYnuing to decrease? • Do changes in survival account for the observed changes in density? • Is crossbill survivorship related to climate? • Is cone producYvity decreasing?
- 30. INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS CONE PRODUCTIVITY
- 31. INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS CONE PRODUCTIVITY ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● Year Meancones/branch/year±1SE 1997 1999 2001 2003 2005 2007 2009 2011 0.6 0.8 1.0 1.2 1.4 1.6 1.8
- 32. 1. PopulaYon is sYll declining 2. Changes in adult survival account for decline 3. Warmer temperatures decrease survival 4. Cone producYvity is likely not contribuYng to populaYon decline INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS SUMMARY Supports main hypothesis
- 33. INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS MORE HOT DAYS globalchange.gov 1961-‐1971 2080-‐2099
- 34. Current 2020 2050 2080 c d Fig. 5 a–d Prediction of lodgepole pine distribution under current climate and the three future 30- 324 Climatic Change (2011) 105:313–328 Current 2020 a b INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS LODGEPOLE PINE DISTRIBUTION Coops and Waring 2011, Clima;c Change Current 2080
- 35. • Curb global warming INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS MANAGEMENT ACTIONS PopulaYon projecYon using demographic data from 2001-‐2007 0 50 100 150 200 01000200030004000 Year Meancrossbillabundance Mean of 2000 simulaYons Mean Crossbill Abundance Years ExYnct in 50 years
- 36. Reciprocal Selection between Crossbills and Pine Figure 1: Distribution of lodgepole pine (black), locations of study sites, and representative red crossbills (Loxia curvirostra complex) and c the Rocky Mountains (lower right), in the Cypress Hills (upper right), and in the South Hills and Albion Mountains (lower left; modifie Benkman 1999). The crossbills and cones are drawn to relative scale. Red squirrels (Tamiasciurus hudsonicus) are found throughout the r lodgepole pine except in some isolated mountains, including the South Hills (SH), Albion Mountains (AM), and Little Rocky Mountain Tamiasciurus were absent from the Cypress Hills (CH) until they were introduced in 1950. South Hills Type 5 • Curb global warming • Assisted migraYon INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS MANAGEMENT ACTIONS
- 37. • Curb global warming • Assisted migraYon • Plant more lodgepole INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS MANAGEMENT ACTIONS
- 38. ACKNOWLEDGEMENTS Field Assistants • Bayasa Amgalen • Jeff Garcia • Michael Hague • Don Jones • Garrey MacDonald • James Maley • Carolyn Miller • Daniel Schlaepfer • Michael Woodruff • Charlie Wright Funding • US EPA STAR • American Ornithologists’ Union • Berry Biodiversity Center • Program in Ecology • WYGISC GITA • Wyoming Chapter of The Wildlife Society • Zoology and Physiology Department Commiyee • Craig Benkman • Merav Ben-‐David • Daniel Tinker Photo Credits • Gary Dewaghe • Roger Garber • Nasim Mansurov • Nick Neely • Dennis Paulson • Lloyd Spitalnik • USFWS
- 40. MARK-‐RECAPTURE STUDY INTRODUCTION Ÿ ABUNDANCE Ÿ SURVIVAL Ÿ CLIMATE Ÿ CONES Ÿ CONCLUSIONS
Notes de l'éditeur
- Thank you Craig for the introduction and thank you all for coming to the brown bag. Today I will be presenting my thesis work and the title of my presentation is “Are South Hills Crossbills declining with increasing temperatures?”
- We are all familiar with climate change and we are discovering increasing evidence of the threats this poses to biodiversity. These are two iconic species that people in our department study and are declining due to climate warming—the polar bear and American pika. Some scientists fear that we are actually entering a period of mass extinction. Today, I’d like to introduce you to another species that is declining due to climate warming.
- The Red Crossbill is a type of finch that is easily recognizable by its crossed mandibles which it uses to consume seeds from the cones of conifers. Crossbills are really unique in that they are nomadic and move around throughout the year to track emerging cone crops and breed when find good cone crops. This is a map of their geographic distribution. You can see that their range matches pretty closely to the range of conifer forests. Craig has shown that within this range there are multiple types of crossbills that have adapted to different types of conifers. Here are a few examples. You can see that the size of their bill--how deep the bill is—varies with the size of the cones and scales. The bottom two types both use lodgepole but they have very different bill sizes. Type 9 = Pinus contorta latifolia from South Hills = Rocky Mountain Lodgepole Pine Type 5 = Pinus contorta latifolia = Rocky Mountain Lodgepole Pine Type 4 = Pseudotsuga menziesii menziesii = Douglas fir Type 3 = Tsuga heterophylla = Western Hemlock Type 2 = Pinus ponderosa scopulorum = Ponderosa Pine Type 1 = Picea rubens = Red spruce
- So you may remember from 2 weeks ago when Matt Talluto presented his PHD research that lodgepole pine have serotinous cones and that this is an adaptation to fire. Serotiny just means that the cones are closed (as you see here) and the seeds are retained in the cones until high heat conditions occur. In the South Hills, where there are no red squirrels, the main predator on these closed cones are crossbills. In this photo on the bottom you can see a female crossbill using her crossed mandibles to pry open a lodgepole pine cone and extracting the seed with her tongue. Craig has documented a coevolutionary arms race in the South Hills between the lodgepole pine and crossbills where the lodgepole pine are developing thicker and larger scales on their cones to prevent predation from crossbills and the crossbills are responding by evolving larger bills to get into those cones. This evolutionary process is making the South Hills Crossbill more and more distinct from the other types of Red Crossbills. In fact, in 2009 Craig and colleagues published a paper recommending they be recognized as a separate species.
- So let’s zoom in a bit more to the home of the South Hills Crossbill. The SHCR occurs in two small mountain ranges in south-central Idaho, right on the border with Nevada and Utah. These two areas are the South Hills and Albions. The outer boundary is the Sawtooth National Forest boundary and the small green patches are all the lodgepole pine. All the lodgepole pine occupies an area of 70 km2. I focused my study on the South Hills, this portion on the left where about 65km2 of lodgepole pine occur.
- Another thing to note about the habitat at the site is just how patchy the forest is. The South Hills are very topographically rich and the forest occurs in small patches interspersed with sagebrush. So the only really suitable habitat for the crossbill are the actual patches of lodgepole, where they nest and forage. Also, the lodgepole pine in the South Hills has a rate of about 92% serotiny. Remember that serotinous cones are an adaptation for fire and that the cones typically stay on the tree until exposed to high heat. This creates a great food resource for the crossbills because they forage on cones that are about 5-8 years old, so they have weathered a little bit and it’s easier to open the scales and extract the seeds. Here you see a crossbill sitting in a mature lodgepole with many years of cones retained on the branches.
- Craig has been studying this population since 1998. Previous work by Craig and former students has shown that this population is declining rapidly. Here you see density declining from 2003-2008. The population declined by 63% in just 6 years.
- The main hypothesis of why the SHCR is declining is that their food supply is being reduced by climate change. As it gets warmer, the temperature experienced by the cones increases enough that they open. And when they open the seeds fall out of the cones. Once the seeds fall out onto the ground, the crossbills cannot find them so there is less food for them. So as the cones open up, there are fewer crossbills.
- So for my research, I explored this hypothesis by asking the following questions.
- So let’s start with the first question…
- In order to get at crossbill abundance, I conducted point counts at 74 sites across the SH in lodgepole forest. The green here represents lodgepole and the red dots are the point count locations. As you can see, they are spread across the core part of their range.
- The point counts were 10 minutes with all crossbills detected in those 10 minutes recorded. The distance to the location of the birds when they were first detected was measured with a laser range finder so that I could use distance sampling analysis. Mornings, JULY-AUGUST, 2003-2012
- I found that from 2003 to 2012 SHCR has continued to decline quite precipitously. 2009 was excluded because incorrect protocol was used. Dropped by 75% from 277 to 71 birds / km2 in just 10 years. What this amounts to is about a 14% decline annually.
- To put this in perspective, the Bicknell’s Thrush is declining at a rate of between 7 and 19%, Cerulean Warblers about 3% a year, and Rusty Blackbirds at least 10% a year. Each of these species are of high conservation concern, are recognized as Vulnerable by the IUCN (International Union for the Conservation of Nature), and working groups have developed for each of these species to prevent their extinction.
- The second question I asked was….
- In order to answer that question, I first had to estimate survival. A well-established way to estimate survival is to use a mark-recapture study. Mark-recapture study means that you catch a bunch of birds, put some sort of unique identifying marker on them, and then either recapture them or resight them in the field to track their survival over time. So I captured birds in a mist net, put unique F&WS bands and colored band combinations on them, took a slieu of measurements, recorded their call type on release to make sure they were South Hills type, and then resighted or recaptured them in future years. This is a photo from a wildlife camera trap I set out the last few years to increase the number of resights.
- So what I ended up with is some data that looked something like this. Make it clear that this is example data. Walk through line by line…we can estimate the likelihood that Bird3 was alive in years 2, 3, and 4 based on all the capture histories. But actually, if we see a bird in any given year, it not only has to be alive (survival probability) but also has to be recaptured or resighted, so we also get an estimate of capture probability. Both survival and capture probability can be modeled as a function of year and sex.
- I used a program called MARK to analyze my data. MARK analysis is conducted in an information theory framework so I selected models using AIC. Since I was more interested in survival than capture probability, I first simplified the recapture part of my model and then looked at survival. Recapture: p~time+sex, what this means is that the capture probability varies by year and that male capture probability is consistently higher than for females Survival: then I modeled survival, but there was no clear best model so I used model-averaging to come up with Here is what I found for survival probability…
- There was no clear best model to predict survival, so I model-averaged across all the survival models I tested. These are the results, survival on the y-axis and year on the x-axis. There was no linear trend over time, but if you look at just the means (the dots) it looks like the first few years were relatively high, then it was low, and the last year was higher. Perhaps this period of low survival was enough to cause the decline I showed you earlier.
- To find out, I projected what the density of crossbills would be given the adult survival rate. I used the first year of density from the point counts to calculate what fecundity had to be to create a stable population. I then held fecundity and juvenile survival constant while I calculated what the next year’s density would be based on the adult survival estimate I got from the capture-recapture analysis.
- Here are the projections, clearly a decline.
- And it matches well with the density I calculated independently using the point count data.
- So we know that the population is declining based on two different estimates and that adult survival could be causing this decline. Is adult survival linked to climate?
- Fortunately there is a weather station in the center of the South Hills <2km from the place we band and it has been collecting temperature and precipitation data continuously since 1989. I used these data to calculate annual climate covariates. Number of hot dry days (90F) (this was calculated using time lags of 1-5 years both in unweighted and weighted fashion for each time lag for a total of 15 covariates) Mean spring Mean summer Mean annual Mean non-breeding Number cold wet days (40F)
- I again used program MARK to include climate as a covariate for survival. Remind people what phi and p mean. P is the best model. Phi is only one climate covariate. These are the top 6 models and I included the year model and constant models for comparison. The top two models are clearly better than than a simple year-effect. deltaAIC <2 indicates strong support for those models, which corresponds with the weight in the next column. The last column shows how much of the variation in survival is accounted for by the climate covariate and is calculated based on deviance.
- If I plot survival against mean temperature in the nonbreeding season, we can see that there is indeed a very strong relationship. Compare that to the second best model, the number of hot days, which also shows a strong relationship. So it looks like indeed survival is related to climate.
- Lastly, I asked if cone productivity was decreasing because if there are fewer cones then that would likely explain the decline in crossbills.
- Because lodgepole pine retains its cones, and no squirrels removing cones, there is a record of cone production. I was able to count the number of cones produced each year. I used annual scars on the branches to differentiate between years.
- This is what I found. There does not seem to be a decline in cone productivity. So we probably don’t have to worry about that for now.
- I can interpret these findings in that they are consistent with my main hypothesis.
- Not only average temp but number hot days will increase
- Why don’t they migrate? As mentioned in intro, they are resident and not competitive with other crossbill types for other food resources
- Is there anything we can do to prevent them from going extinct?
- Genotype of lodgepole
- I captured adult males and females. I also captured and marked juveniles. A portion of the birds have a disease called scaley-leg mites. It makes their skin rough, can cause swelling, and they can even lose some of their toes, so we couldn’t put metal bands on them, only larger plastic bands so we didn’t cause further aggravation to their legs. For a number of reasons I won’t be talking about the juveniles or mite birds today.