diff --git a/DESCRIPTION b/DESCRIPTION
index 035ef58..1500851 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -16,7 +16,7 @@ Description: A simple way of fitting detection functions to distance sampling
     Horvitz-Thompson-like estimator) if survey area information is provided. See
     Miller et al. (2019) <doi:10.18637/jss.v089.i01> for more information on
     methods and <https://examples.distancesampling.org/> for example analyses.
-Version: 2.0.0.9005
+Version: 2.0.0.9006
 URL: https://github.com/DistanceDevelopment/Distance/
 BugReports: https://github.com/DistanceDevelopment/Distance/issues
 Language: en-GB
diff --git a/docs/articles/covariates-distill.html b/docs/articles/covariates-distill.html
index 4a4e7ec..2da502d 100644
--- a/docs/articles/covariates-distill.html
+++ b/docs/articles/covariates-distill.html
@@ -1,12 +1,18 @@
 <!DOCTYPE html>
-<!-- Generated by pkgdown: do not edit by hand --><html lang="en">
+<!-- Generated by pkgdown: do not edit by hand --><html lang="en-GB">
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <meta charset="utf-8">
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
 <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
 <title>Incorporating covariates in the detection function • Distance</title>
-<script src="../deps/jquery-3.6.0/jquery-3.6.0.min.js"></script><meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
+<!-- mathjax math --><script src="https://cdn.jsdelivr.net/npm/mathjax@3.2.2/es5/tex-mml-chtml.js" integrity="sha256-MASABpB4tYktI2Oitl4t+78w/lyA+D7b/s9GEP0JOGI=" crossorigin="anonymous"></script><script>
+  window.MathJax = {
+    chtml: {
+      fontURL: "https://cdn.jsdelivr.net/npm/mathjax@3.2.2/es5/output/chtml/fonts/woff-v2"
+    }
+  };
+</script><script src="../deps/jquery-3.6.0/jquery-3.6.0.min.js"></script><meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
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diff --git a/docs/articles/covariates-distill_files/figure-html/basic-1.png b/docs/articles/covariates-distill_files/figure-html/basic-1.png
index 0dabd4e..a37b35e 100644
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diff --git a/docs/articles/covariates-distill_files/figure-html/box-1.png b/docs/articles/covariates-distill_files/figure-html/box-1.png
index 30a286d..aadb810 100644
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diff --git a/docs/articles/lines-distill.html b/docs/articles/lines-distill.html
index fe5c8d0..4616dbc 100644
--- a/docs/articles/lines-distill.html
+++ b/docs/articles/lines-distill.html
@@ -32,7 +32,7 @@
 
     <a class="navbar-brand me-2" href="../index.html">Distance</a>
 
-    <small class="nav-text text-muted me-auto" data-bs-toggle="tooltip" data-bs-placement="bottom" title="">2.0.0.9004</small>
+    <small class="nav-text text-muted me-auto" data-bs-toggle="tooltip" data-bs-placement="bottom" title="">2.0.0.9005</small>
 
 
     <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbar" aria-controls="navbar" aria-expanded="false" aria-label="Toggle navigation">
@@ -107,7 +107,7 @@ <h2 id="survey-design">Survey design<a class="anchor" aria-label="anchor" href="
 <p>Nineteen line transects were walked twice (Figure <a href="#fig:fig">1</a>).</p>
 <div class="figure">
 <span style="display:block;" id="fig:fig"></span>
-<img src="montrave.JPG" alt="Montrave study area; diagonal lines indicate line transects walked to generate these data." width="499"><p class="caption">
+<img src="montrave.jpg" alt="Montrave study area; diagonal lines indicate line transects walked to generate these data." width="499"><p class="caption">
 Figure 1: Montrave study area; diagonal lines indicate line transects walked to generate these data.
 </p>
 </div>
@@ -352,8 +352,6 @@ <h2 id="model-comparison-tables">Model comparison tables<a class="anchor" aria-l
 <div class="sourceCode" id="cb18"><pre class="downlit sourceCode r">
 <code class="sourceCode R"><span><span class="fu">knitr</span><span class="fu">::</span><span class="fu"><a href="https://rdrr.io/pkg/knitr/man/kable.html" class="external-link">kable</a></span><span class="op">(</span><span class="fu"><a href="../reference/summarize_ds_models.html">summarize_ds_models</a></span><span class="op">(</span><span class="va">wren.hn</span>, <span class="va">wren.hr.poly</span>, <span class="va">wren.unif.cos</span><span class="op">)</span>,digits<span class="op">=</span><span class="fl">3</span>,</span>
 <span>             caption<span class="op">=</span><span class="st">"Model comparison table for wren line transect data, Montrave."</span><span class="op">)</span></span></code></pre></div>
-<pre><code><span><span class="co">## Warning: Passing models via ... will be depricated in the next release, please</span></span>
-<span><span class="co">## pass models in a list using the models argument.</span></span></code></pre>
 <table class="table">
 <caption>
 <span id="tab:unnamed-chunk-11">Table 1: </span>Model comparison table for wren line transect data, Montrave.</caption>
@@ -415,7 +413,7 @@ <h2 id="model-comparison-tables">Model comparison tables<a class="anchor" aria-l
 <h3 id="model-selection-is-not-a-cookbook">Model selection is not a cookbook<a class="anchor" aria-label="anchor" href="#model-selection-is-not-a-cookbook"></a>
 </h3>
 <p>The AIC model selection tools suggest the hazard rate key function is the preferred model. However, examine the shape of the hazard rate detection function in contrast to the uniform cosine fitted detection function (Figure <a href="#fig:evasive">5</a>).</p>
-<div class="sourceCode" id="cb20"><pre class="downlit sourceCode r">
+<div class="sourceCode" id="cb19"><pre class="downlit sourceCode r">
 <code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/graphics/plot.default.html" class="external-link">plot</a></span><span class="op">(</span><span class="va">wren.hr.poly</span>, breaks<span class="op">=</span><span class="va">cutpoints</span>, main<span class="op">=</span><span class="st">"Hazard rate"</span><span class="op">)</span></span>
 <span><span class="fu"><a href="https://rdrr.io/r/graphics/plot.default.html" class="external-link">plot</a></span><span class="op">(</span><span class="va">wren.unif.cos</span>, breaks<span class="op">=</span><span class="va">cutpoints</span>, main<span class="op">=</span><span class="st">"Uniform cosine"</span><span class="op">)</span></span></code></pre></div>
 <div class="figure">
diff --git a/docs/articles/species-covariate-distill.html b/docs/articles/species-covariate-distill.html
index 1f25cdc..96daa8d 100644
--- a/docs/articles/species-covariate-distill.html
+++ b/docs/articles/species-covariate-distill.html
@@ -1,12 +1,18 @@
 <!DOCTYPE html>
-<!-- Generated by pkgdown: do not edit by hand --><html lang="en">
+<!-- Generated by pkgdown: do not edit by hand --><html lang="en-GB">
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <meta charset="utf-8">
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
 <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
 <title>Covariate modeling with rare species • Distance</title>
-<script src="../deps/jquery-3.6.0/jquery-3.6.0.min.js"></script><meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
+<!-- mathjax math --><script src="https://cdn.jsdelivr.net/npm/mathjax@3.2.2/es5/tex-mml-chtml.js" integrity="sha256-MASABpB4tYktI2Oitl4t+78w/lyA+D7b/s9GEP0JOGI=" crossorigin="anonymous"></script><script>
+  window.MathJax = {
+    chtml: {
+      fontURL: "https://cdn.jsdelivr.net/npm/mathjax@3.2.2/es5/output/chtml/fonts/woff-v2"
+    }
+  };
+</script><script src="../deps/jquery-3.6.0/jquery-3.6.0.min.js"></script><meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
 <link href="../deps/bootstrap-5.3.1/bootstrap.min.css" rel="stylesheet">
 <script src="../deps/bootstrap-5.3.1/bootstrap.bundle.min.js"></script><link href="../deps/Roboto-0.4.9/font.css" rel="stylesheet">
 <link href="../deps/font-awesome-6.5.2/css/all.min.css" rel="stylesheet">
@@ -89,7 +95,7 @@ <h4 data-toc-skip class="author">Eric Rexstad</h4>
 <h2 id="background">Background<a class="anchor" aria-label="anchor" href="#background"></a>
 </h2>
 <p>Sometimes the focal species of a distance sampling survey is quite rare. So rare that it is difficult to accumulate sufficient detections to fit a detection function for the species in question. Likewise, it is also common for other species to be detected during the survey for the focal species. Could the detections of the other species be useful in estimating a detection function for the focal species?</p>
-<p>One approach might be to consider the species to serve as “strata” and proceed to analyse the data as if they were from a stratified survey. See the <a href="http://distancesampling.org/Distance/web-only/strata/strata-distill.html" class="external-link">example for stratified survey analysis</a>. However, if a pooled detection function (one that combines data from multiple species) is fitted, it would be dubious to apply this pooled detection function to data at a lower level of aggregation (species level). Applying the pooled detection function would lead to a biased estimate of abundance for the rare species.</p>
+<p>One approach might be to consider the species to serve as “strata” and proceed to analyse the data as if they were from a stratified survey. See the <a href="https://distancesampling.org/Distance/articles/web-only/strata/strata-distill.html" class="external-link">example for stratified survey analysis</a>. However, if a pooled detection function (one that combines data from multiple species) is fitted, it would be dubious to apply this pooled detection function to data at a lower level of aggregation (species level). Applying the pooled detection function would lead to a biased estimate of abundance for the rare species.</p>
 <p>Instead of treating species as strata, an alternative form of analysis is to treat species as a covariate in the modelling of the detection function <span class="citation">(Marques &amp; Buckland, 2003)</span>. The principle is that the general key function is shared across species, but the scale parameter <span class="math inline">\((\sigma)\)</span> differs between species. In this way, the detections of all species is shared, such that the estimation of the detection function for the rare species is bolstered by information from other species; yet the rare species receives its own <em>unique</em> detection function such that bias is not induced in the abundance estimation for that species.</p>
 <p>To demonstrate such an analysis, the Montrave songbird study conducted by Buckland <span class="citation">(2006)</span> is used. The species covariate approach to analysis of the snapshot point count version of his survey is described in the book by Buckland et al. <span class="citation">(2015, sec. 5.3.2.2)</span>. The <code>Distance</code> R package <span class="citation">(Miller, Rexstad, Thomas, Marshall, &amp; Laake, 2019)</span> is used to analyse the line transect survey Buckland conducted. Results are compared with estimates presented by Buckland <span class="citation">(2006)</span>.</p>
 <p>The data are available online at a website that serves as a companion to Buckland et al. <span class="citation">(2015)</span>. The data set can be read into R directly from the URL.</p>
@@ -313,7 +319,7 @@ <h2 id="compare-with-published-estimates">Compare with published estimates<a cla
 <p>The density estimates for chaffinch and great tits match those reported by Buckland <span class="citation">(S. T. Buckland, 2006)</span> almost exactly. The congruence between estimates produced by this analysis and those reported by Buckland are less good for the robins and winter wrens.</p>
 <div class="figure">
 <span style="display:block;" id="fig:screenclip"></span>
-<img src="tab2-buck.png" alt="Reproduction of Table 2 of Buckland (2006)."><p class="caption">
+<img src="tab2-buck.png" alt="Reproduction of Table 2 of Buckland (2006)." width="944"><p class="caption">
 Figure 2: Reproduction of Table 2 of Buckland (2006).
 </p>
 </div>
diff --git a/docs/articles/species-covariate-distill_files/figure-html/plotcode-1.png b/docs/articles/species-covariate-distill_files/figure-html/plotcode-1.png
index fa66fc1..977689d 100644
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diff --git a/docs/articles/web-only/points/pointtransects-distill.html b/docs/articles/web-only/points/pointtransects-distill.html
index 8100f4b..0129948 100644
--- a/docs/articles/web-only/points/pointtransects-distill.html
+++ b/docs/articles/web-only/points/pointtransects-distill.html
@@ -1,12 +1,18 @@
 <!DOCTYPE html>
-<!-- Generated by pkgdown: do not edit by hand --><html lang="en">
+<!-- Generated by pkgdown: do not edit by hand --><html lang="en-GB">
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <meta charset="utf-8">
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
 <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
 <title>Point transect density estimation • Distance</title>
-<script src="../../../deps/jquery-3.6.0/jquery-3.6.0.min.js"></script><meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
+<!-- mathjax math --><script src="https://cdn.jsdelivr.net/npm/mathjax@3.2.2/es5/tex-mml-chtml.js" integrity="sha256-MASABpB4tYktI2Oitl4t+78w/lyA+D7b/s9GEP0JOGI=" crossorigin="anonymous"></script><script>
+  window.MathJax = {
+    chtml: {
+      fontURL: "https://cdn.jsdelivr.net/npm/mathjax@3.2.2/es5/output/chtml/fonts/woff-v2"
+    }
+  };
+</script><script src="../../../deps/jquery-3.6.0/jquery-3.6.0.min.js"></script><meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
 <link href="../../../deps/bootstrap-5.3.1/bootstrap.min.css" rel="stylesheet">
 <script src="../../../deps/bootstrap-5.3.1/bootstrap.bundle.min.js"></script><link href="../../../deps/Roboto-0.4.9/font.css" rel="stylesheet">
 <link href="../../../deps/font-awesome-6.5.2/css/all.min.css" rel="stylesheet">
@@ -102,7 +108,7 @@ <h2 id="survey-design">Survey design<a class="anchor" aria-label="anchor" href="
 <p>A total of 373 point transects were placed in three pastures in the Arapaho National Wildlife Refuge in Colorado (Figure <a href="#fig:fig">1</a>). Elevation of these pastures was ~2500m. We will not deal with pasture-level analysis of these data in this vignette and will alter the data to remove the strata designations.</p>
 <div class="figure">
 <span style="display:block;" id="fig:fig"></span>
-<img src="arapaho.JPG" alt="Summer grazed pastures along Illinois River Arapaho National Wildlife Refuge, Colorado.  Figure from [@knopf_guild_1988]."><p class="caption">
+<img src="arapaho.jpg" alt="Summer grazed pastures along Illinois River Arapaho National Wildlife Refuge, Colorado.  Figure from [@knopf_guild_1988]." width="320"><p class="caption">
 Figure 1: Summer grazed pastures along Illinois River Arapaho National Wildlife Refuge, Colorado. Figure from <span class="citation">(Knopf et al., 1988)</span>.
 </p>
 </div>
@@ -291,6 +297,9 @@ <h2 id="specifying-different-detection-functions">Specifying different detection
 <span>                   transect<span class="op">=</span><span class="st">"point"</span>, convert_units<span class="op">=</span><span class="va">conversion.factor</span>, truncation<span class="op">=</span><span class="st">"5%"</span><span class="op">)</span></span></code></pre></div>
 <pre><code><span><span class="co">## Warning in ddf.ds(dsmodel = dsmodel, data = data, meta.data = meta.data, :</span></span>
 <span><span class="co">## Estimated hazard-rate scale parameter close to 0 (on log scale). Possible</span></span>
+<span><span class="co">## problem in data (e.g., spike near zero distance).</span></span>
+<span><span class="co">## Warning in ddf.ds(dsmodel = dsmodel, data = data, meta.data = meta.data, :</span></span>
+<span><span class="co">## Estimated hazard-rate scale parameter close to 0 (on log scale). Possible</span></span>
 <span><span class="co">## problem in data (e.g., spike near zero distance).</span></span></code></pre>
 </div>
 <div class="section level2">
diff --git a/docs/articles/web-only/points/pointtransects-distill_files/figure-html/basichist-1.png b/docs/articles/web-only/points/pointtransects-distill_files/figure-html/basichist-1.png
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diff --git a/docs/articles/web-only/strata/strata-distill.html b/docs/articles/web-only/strata/strata-distill.html
index 0c423a8..ddd3fcc 100644
--- a/docs/articles/web-only/strata/strata-distill.html
+++ b/docs/articles/web-only/strata/strata-distill.html
@@ -1,12 +1,18 @@
 <!DOCTYPE html>
-<!-- Generated by pkgdown: do not edit by hand --><html lang="en">
+<!-- Generated by pkgdown: do not edit by hand --><html lang="en-GB">
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <meta charset="utf-8">
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
 <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
 <title>Analysis of stratified survey designs • Distance</title>
-<script src="../../../deps/jquery-3.6.0/jquery-3.6.0.min.js"></script><meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
+<!-- mathjax math --><script src="https://cdn.jsdelivr.net/npm/mathjax@3.2.2/es5/tex-mml-chtml.js" integrity="sha256-MASABpB4tYktI2Oitl4t+78w/lyA+D7b/s9GEP0JOGI=" crossorigin="anonymous"></script><script>
+  window.MathJax = {
+    chtml: {
+      fontURL: "https://cdn.jsdelivr.net/npm/mathjax@3.2.2/es5/output/chtml/fonts/woff-v2"
+    }
+  };
+</script><script src="../../../deps/jquery-3.6.0/jquery-3.6.0.min.js"></script><meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
 <link href="../../../deps/bootstrap-5.3.1/bootstrap.min.css" rel="stylesheet">
 <script src="../../../deps/bootstrap-5.3.1/bootstrap.bundle.min.js"></script><link href="../../../deps/Roboto-0.4.9/font.css" rel="stylesheet">
 <link href="../../../deps/font-awesome-6.5.2/css/all.min.css" rel="stylesheet">
@@ -101,8 +107,8 @@ <h2 id="survey-design">Survey design<a class="anchor" aria-label="anchor" href="
 <p>A total of 373 point transects were placed in three pastures in the Arapaho National Wildlife Refuge in Colorado (Figure <a href="#fig:fig">1</a>). Elevation of these pastures was ~2500m. In this example, we <strong>will</strong> perform pasture-level analysis of these data.</p>
 <div class="figure">
 <span style="display:block;" id="fig:fig"></span>
-<img src="arapaho.JPG" alt="Summer grazed pastures along Illinois River Arapaho National Wildlife Refuge, Colorado.
-Figure from [@knopf_guild_1988]."><p class="caption">
+<img src="arapaho.jpg" alt="Summer grazed pastures along Illinois River Arapaho National Wildlife Refuge, Colorado.
+Figure from [@knopf_guild_1988]." width="320"><p class="caption">
 Figure 1: Summer grazed pastures along Illinois River Arapaho National Wildlife Refuge, Colorado.
 Figure from <span class="citation">(Knopf et al., 1988)</span>.
 </p>
diff --git a/docs/articles/web-only/strata/strata-distill_files/figure-html/threeplot-1.png b/docs/articles/web-only/strata/strata-distill_files/figure-html/threeplot-1.png
index 0b1d208..8929a49 100644
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diff --git a/vignettes/lines-distill.Rmd b/vignettes/lines-distill.Rmd
index 3958d9c..aa574a8 100644
--- a/vignettes/lines-distill.Rmd
+++ b/vignettes/lines-distill.Rmd
@@ -41,7 +41,7 @@ In this exercise, we use `R` [@r_core_team_r_2019] and the `Distance` package [@
 Nineteen line transects were walked twice (Figure \@ref(fig:fig)). 
 
 ```{r fig, echo=FALSE, fig.cap="Montrave study area; diagonal lines indicate line transects walked to generate these data.", outwidth='100%', eval=TRUE}
-knitr::include_graphics("montrave.JPG")
+knitr::include_graphics("montrave.jpg")
 ```
 
 The fields of the `wren_lt` data set are:
diff --git a/vignettes/species-covariate-distill.Rmd b/vignettes/species-covariate-distill.Rmd
index 5c938a7..76162e5 100644
--- a/vignettes/species-covariate-distill.Rmd
+++ b/vignettes/species-covariate-distill.Rmd
@@ -34,7 +34,7 @@ options(kableExtra.html.bsTable = TRUE)
   
 Sometimes the focal species of a distance sampling survey is quite rare.  So rare that it is difficult to accumulate sufficient detections to fit a detection function for the species in question.  Likewise, it is also common for other species to be detected during the survey for the focal species.  Could the detections of the other species be useful in estimating a detection function for the focal species?
 
-One approach might be to consider the species to serve as "strata" and proceed to analyse the data as if they were from a stratified survey.  See the [example for stratified survey analysis](http://distancesampling.org/Distance/web-only/strata/strata-distill.html).  However, if a pooled detection function (one that combines data from multiple species) is fitted, it would be dubious to apply this pooled detection function to data at a lower level of aggregation (species level).  Applying the pooled detection function would lead to a biased estimate of abundance for the rare species.
+One approach might be to consider the species to serve as "strata" and proceed to analyse the data as if they were from a stratified survey.  See the [example for stratified survey analysis](https://distancesampling.org/Distance/articles/web-only/strata/strata-distill.html).  However, if a pooled detection function (one that combines data from multiple species) is fitted, it would be dubious to apply this pooled detection function to data at a lower level of aggregation (species level).  Applying the pooled detection function would lead to a biased estimate of abundance for the rare species.
 
 Instead of treating species as strata, an alternative form of analysis is to treat species as a covariate in the modelling of the detection function [@FMARBUC03].  The principle is that the general key function is shared across species, but the scale parameter $(\sigma)$ differs between species.  In this way, the detections of all species is shared, such that the estimation of the detection function for the rare species is bolstered by information from other species; yet the rare species receives its own *unique* detection function such that bias is not induced in the abundance estimation for that species.
 
diff --git a/vignettes/web-only/points/pointtransects-distill.Rmd b/vignettes/web-only/points/pointtransects-distill.Rmd
index 2c2ba9c..01e9ce0 100644
--- a/vignettes/web-only/points/pointtransects-distill.Rmd
+++ b/vignettes/web-only/points/pointtransects-distill.Rmd
@@ -43,7 +43,7 @@ Steps in this analysis are similar to the steps taken in the [line transect anal
 A total of 373 point transects were placed in three pastures in the Arapaho National Wildlife Refuge in Colorado (Figure \@ref(fig:fig)).  Elevation of these pastures was ~2500m.  We will not deal with pasture-level analysis of these data in this vignette and will alter the data to remove the strata designations.
 
 ```{r fig, echo=FALSE, fig.dim=c(7,5), fig.cap="Summer grazed pastures along Illinois River Arapaho National Wildlife Refuge, Colorado.  Figure from [@knopf_guild_1988]."}
-knitr::include_graphics("arapaho.JPG")
+knitr::include_graphics("arapaho.jpg")
 ```
 
 
